We present Monte-Carlo calculations based on extended core-accretion planet formation models taking into account disk structure and evolution and migration of the protoplanet. These models lead to giant planet formation timescales compatible with disk lifetimes.
For different initial conditions, we calculate the evolution of a disk and an embryo that may form a giant planet. The initial conditions are in particular the disk mass, disk lifetime and metallicity of the system.
Using observed distributions for these initial conditions, and taking into account the observational bias introduced by radial velocity surveys, we will compare in a statistical way the results of our models and the population of know extrasolar planets.
Río Tinto is an extreme acidic river that is the result of the action of subsurface geomicrobiology on the complex sulfides of the Iberian Pyritic Belt (MARTE project). The Tinto ecosystem is controlled by iron. Different iron minerals can be found in the Tinto basin as products of this geomicrobiological activity. The higher solubility of sulfates over iron hydroxides and the acidic nature of ferric iron promotes a gradual enrichment in sulfates along the river. The geobiological properties of this extant iron world raises the question of its feasibility both during our Archaean when ocean iron concentration several orders of magnitude higher than nowadays, or on Mars, in light of the latest reports from the ongoing missions.
Understanding the composition, geology, environment, dynamics and astrobiology potential of icy satellites could elucidate us about the formation of the solar system and its potential to harbor life. Consequently, in the Solar System Exploration Decadal Survey (2002) the National Research Council (NRC) identified the exploration of Europa, Jupiter's icy satellite, as the highest priority science objective to be addressed through the flagship class mission category. According to NASA's Solar System Exploration Roadmap (2006), follow up missions could target other icy moons, such as Saturn's Titan, and Neptune's Triton. Furthermore, based on recent discoveries by the Cassini orbiter, Enceladus also became a significant target of interest. In-situ exploration of these moons is highly desirable, in order to complement and validate orbital remote sensing measurements. In this paper we discuss mission architecture options and technology challenges for icy body landers, with a special focus on three small Europa lander concepts and on a Triton lander concept. In the same context we also address two other icy moons, Enceladus and Titan. The mass allocation for this type of landers is driven by mission architecture and technology considerations. We demonstrate that in all cases a significant fraction potentially well over 50% of the entry mass is required to slow down and to land the spacecraft. Europa, Triton and Enceladus are airless bodies, where a lander must remove most or all of its excess velocity through propulsive means. We address various landing methods through a comparison between soft and hard landers and impactors. On Titan, however, the atmosphere could be utilized for an aeroassist maneuver to remove most of the entry velocity, by employing an aeroshell and parachutes. We also discuss the potentially available mass fractions for strawman science payloads expected in the range of 2.5% to 10%. Extreme environments at these destinations have a significant impact on the mission and technology trade space. Low temperature electronics, high radiation tolerant electronics and radioisotope power systems (RPS) could extend mission lifetime; while advanced propellants could increase payload mass fraction. We address power system trades between batteries and RPSs as a function of in-situ mission duration. Additional challenges for a landed mission will be also discussed, which could include potential contamination of the landing site by the propulsion system; planetary protection issues; terrain uncertainty during and after landing; communication constraints between the lander and orbiter or Earth; and the design of a suitable sampling mechanism. Consequently, in this paper we provide an overview of mission architecture and technology trade space options and challenges, which could enable potential future mass limited landers to mitigate the encountered extreme environments, while exploring these icy satellites of our outer solar system in line with the Vision for Space Exploration.
Based on the comparison of its hydrogeochemistry with the geochemical features of the alteration mineralogy of meteoritic precursors and with Galileo`s NIMS data, Tirez Lake (Spain) is proposed as a terrestrial analogue of the Europa's ocean. Hydrogeochemical and mineralogical analyses showed that Tirez waters corresponded to Mg-Na-SO4-Cl brines with epsomite, hexahydrite and halite as end members. Frozen Tirez brines were analyzed by FTIR, providing similar spectra to the Galileo spectral data. Calorimetric measurements of Tírez brines showed pathways and phase metastability for magnesium sulfate and sodium chloride crystallization which may aid in understanding the processes involved in the formation of Europa's icy crust. Biological aspects of Tirez lake will be described in Gomez F. presentation (this issue)
The number of exoplanets newly discovered increases rapidly with time. Those detections are, however, still indirect, via radial velocity surveys and photometric transits, and still very little is known about their atmospheric properties. Despite this lack of direct observations, many efforts are devoted to the modelling of exo-planet atmospheres. I will review the current status of giant planet atmosphere models, and describe their main properties. I will also describe the properties of planets orbiting their parent star at close orbital distances. The former undergo irradiation effects from their parent star and eventually evaporation effects. Both processes can severely affect the properties of close-in planets, in terms of atmosphere structure, emitted flux and evolution.
Titan shows a variegated surface to the Cassini orbiter in near-infrared reflection. The equatorial regions are a vast, dark dunefield intersperced with brighter material including unique Xanadu; the mid-latitudes are bright, but spectrally distinct from the equatorial brightlands; and the south pole is again a mixture of bright and dark, with the different dark material than that near the equator. Two distinct 5-micron-bright areas adorn the leading hemisphere. We present color global mapping of Titan and spectral unit maps of Titan's surface generated using principal components and cluster analyses. We discuss these results in the context of returns from Huygens and RADAR to paint a global picture of Titan's state and evolution.
Trans-Neptunian objects and Centaurs contain the least processed material accessible to direct investigation and they can provide important clues on the processes that were operating in the protoplanetary nebula. The study of these objects can help in understanding the accretion processes which governed the planetary formation, as well as those of other dust star disks.
Studies of the physical and chemical properties of these icy bodies are still limited by the faintness of these objects, even if observed with the worldwide largest telescopes. Recent observations in visible photometry have provided B, V, R and I high quality colors for more than 130 objects. The color diversity is now a reality in the TNOs population. Relevant statistical analysis have been performed and all possible correlations between optical colors and orbital parameters have been analyzed. A taxonomy scheme based on multivariate statistical analysis of a subsample described by the 4 color indices (B-V, V-R, V-I and V-J) has been obtained. A tentative interpretation of the obtained groups in terms of surface characteristics is given.
Visible and infrared spectra are available for about 30 objects. The wavelength region ranging 0.4 - 2.3 microns encompass diagnostic spectral features to investigate on organic compounds, minerals and ices present on the surface of the TNOs. While some show no diagnostic spectral bands, others have surface deposits of ices of H20, CH4, and N2 sharing these properties with Pluto and Triton. The investigation of the surface variation can be diagnostic of possible composition diversity and/or different evolution with different physical processes affecting the surface.
The state of art on the knowledge of the surface properties and composition of the population will be presented, analyzed and interpreted. Possible surface alteration will be investigate and discussed.
In 2004, the Cosmic Dust Analyzer (CDA) onboard the spacecraft Cassini detected dust streams of nanometer-sized particles up to 1 AU (Astronomical Unit » 1.5 ·1011m) away from Saturn.
Backtracking the particles path showed that their origin lay inside the Saturnian system.
The creation process of these dust streams is understood: tiny grains are charged up by Saturn's surrounding plasma and get accelerated inside Saturn's magnetosphere. Due to their large charge to mass ratio, the particles reach escape velocity and leave the Saturnian system. But the particles' sources are still unknown.
Additionally, this particle population is difficult to detect by CDA inside Saturn's magnetosphere. The dominant part of the dust measurements are micron-sized dust particles, which build the E ring, Saturn's largest ring.
Here we present a model calculation of tiny particles inside Saturn's magnetosphere. First estimates of their sources and their differences to bounded dust particles are given.
The present Mars missions, coupling in situ measurements in two selected sites by the NASA rovers, to orbital coverage, in particular through the ESA/Mars Express, offer an in-depth revisiting of the long-term Mars History, with a special emphasis on the role water played. We will discuss the most recent discoveries, with relevance to the possibility for Mars to have hosted habitats in its early times.
On July 4, 2005 NASA's Deep Impact sent a 375 kg impactor into the nucleus of comet 9P/Tempel 1. We report here on the results of the Chandra observations of the Deep Impact encounter. Comets emit X-rays when highly charged ions from the solar wind charge exchange with its neutral coma. Because of the comet's low outgassing rate it was collisionally thin to charge exchange. Freshly released gas should therefore directly increase the emission measure, allowing Chandra to detect gas created by the impact. The nearly 30 day time span of our observations sampled several severe changes in the solar wind and outbursts in the comet's activity, which can be clearly identified in the observed X-ray emission morphology, spectra and long term light curve.
Charge exchange emission in (soft) X-ray results from the interaction between the solar wind and comets, planets and the ISM. Depending strongly on velocity and target species, this emission can be regarded as a fingerprint of the underlying interaction. This can open a new window on local plasma conditions, thusfar only accessible by space exploration - given sufficient knowledge is available about charge exchange. We studied these reactions in the laboratory with special emphasis on collisions between He2+ and gasses characteristic for cometary and planetary atmospheres. The data are used to demonstrate the diagnostics of charge exchange emission by analyzing EUVE observations of comets Hyakutake and Hale-Bopp in terms of solar wind and coma quantities.
The Juno mission, currently in Phase B, was selected by NASA to be the second mission in the New Frontiers Program. The overarching scientific goal of the Juno mission is to understand the origin and evolution of Jupiter. As the archetype of giant planets, Jupiter can provide the knowledge we need to understand the origin of our own solar system and the planetary systems being discovered around other stars. Juno's investigation of Jupiter focuses on four themes: Origin, Interior Structure, Atmospheric Composition and Dynamics, and the Polar Magnetosphere.
The scientific measurements include global maps of the gravity and magnetic fields, microwave radiometry of Jupiter's deep atmosphere and fields and particles measurements of Jupiter's polar magnetosphere. Juno's 32 polar orbits extensively sample Jupiter's full range of latitudes and longitudes. High sensitivity radiometric measurements yield a 3-dimensional view of Jupiter's deep atmosphere (down to >100 bars) and will be used to infer the global abundance of water, and to investigate the deep atmosphere's complex meteorology. Determining the Jovian water abundance permits discrimination between various scenarios of the formation of Jupiter. The gravity data constrain the planet's interior rotation, core size and interior structure. The magnetic field measurements investigate how the interior dynamo works and examine the depth of generation of Jupiter's powerful magnetic field. Fields and particles measurements as well as UV polar images investigate Jupiter's auroral physi! cs to determine what drives Jupiter's remarkable northern and southern lights.
An overview of the mission and science objectives will be presented.
The electromagnetic interaction between Io and Jupiter leads to single or multiple auroral UV spots in both jovian hemispheres. This study concentrates on short timescale ( 1 min) morphological changes of the footprints. In order to achieve a sufficient time resolution, we use the time-tag mode of the HST/STIS instrument. This allows us to account for the spots blurring due to the rapid evolution of the jovian magnetic field lines. In addition to the spots motion, our analysis focuses on the spots brightness variations and on the correlation between these variations. The characterisation of the parameters herein gives rise to both clues and new questions on the mechanisms that induce the precipitation of energetic electrons.
Comet C/NEAT (2001 Q4) was observed in three consecutive nights in May 2004 (19th, 20th and 21th) with the 2m Ritchey-Chretien-Coude telescope and the 2-Channel Focal Reducer at the Bulgarian National Astronomical Observatory -Rzhen. Narrow-band filters were used, centered on the blue and red comets' continuum at 443 nm and 642 nm, respectively. The images were calibrated to intensities using spectrophotometric standard star observed at the same airmass. The raw images show irregularity of the dust coma in the direction to the Sun. After applying a numerical filter jet-like structures are visible. For the description of these features a Monte-Carlo model, based on Finson-Probstein theory for dust particles dynamics, is developed. The size of the active region, its coordinates on the nucleus surface, and the range of the dust particles' sizes were found by trial and error. Fixed values of the particle size distribution, the rotational period and the orientation of the rotation axis were adopted. The contribution of the structures to the total intensity of the dust coma is 4-5size of the active region. This suggests that the source region of the observed structures is 10 times more active than the remaining nucleus surface. The images obtained at both continuum wavelengths were used to produce color maps of the dust coma. The color of the structure does not deviate strongly from the color of the ambient dust coma.
It is now quite clear that there are no large expanses of liquid organics on Titan detectable by Cassini's optical instruments. Unless photochemical models are quite wrong, it is difficult to account for the absence of the predicted simple organics. A possible way out of the conundrum is that some fraction of the simple organics on Titan is tied up in polar ice deposits consisting of ethane mixed with enough other organics to raise its freezing point enough to keep it solid over some range of latitudes on Titan. To investigate this hypothesis, I have constructed a simple model of polar cap formation on Titan that employs 1-dimensional, glacial-flow, combined with assumptions about the extent and rate of solid precipitation on Titan. The calculations will be presented and conclusions drawn as to the total volatile inventory and latitudinal extent of Titan's hypothetical polar caps.
On July 4, 2005 the NASA spacecraft Deep Impact delivered an impactor on the comet 9P/Tempel 1 to study the material ejected from the nucleus. A worldwide observation campaign accompanied the mission, to characterize the activity of Tempel 1 before and after the impact. At La Palma (Canary Islands), the comet was observed from July 2 to July 9 using the echelle spectrograph SARG on the Telescopio Nazionale Galileo (TNG). 15 spectra have been obtained in the spectral range 4620-7920 Å with a resolving power R=29000. Most of the lines found in the spectra can be attributed to C2, NH2 and CN; the atomic oxygen lines, both the green line at 5577 Å and the red doublet at 6300 and 6364 Å are clearly visible in every spectrum. The intensity ratio between the green line and the sum of the red lines, indicative of the parent of these lines, has been computed for most of the spectra and seems to point to water. Only the ratio computed on the spectra taken few hours after the impact has a slightly different value.
New spacecraft data, material parameters and better heat transfer theories, yield outer planet satellite interiors colder than previously thought. While there are observations indicating that these satellites are very cold (e.g., heavily cratered surfaces, non-hydrostatic shapes), there are also numerous indications of endogenic activity: tidally driven dynamical evolution (e.g., Iapetus' synchronous state), geology (e.g., Enceladus' geysers), and differentiated interiors that require the production of a large amount of heat. Existing models are not favorable for developing tidal dissipation as a driver for endogenic activity and dynamical evolution. We show new models that include (1) initial porosity;, (2) short-lived radionuclides that can melt most or all of the ice and can make the interior dissipative for enabling tidally driven processes. This work was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract.
Since the Voyager missions, Galileo and Cassini-Huygens have explored in detail the satellite systems of Jupiter and Saturn, respectively. Laboratory experiments have improved our knowledge of material properties relevant to the satellites. Advances in geophysical modeling have provided new views of the interior, exterior, and orbital evolution. We present new approaches that allow to understand how small satellites can be significantly more geologically-dynamically active than previously thought (e.g., Enceladus' geysers); and to solve long-standing riddles (e.g., Iapetus' synchronous rotation). These new models involve the presence in the early outer Solar system of short-lived radiogenic species. We discuss the implications of these new results, e.g., fine-scale radiochronometry of satellites and constraints on the environment in which they formed and evolved. This work was carried out by the Jet Propulsion Laboratory, California Institute of Technology, under NASA contract.
The atmospheres of the three terrestrial planets (Venus, Earth, Mars) are thought to have evolved from a relatively similar initial state to the present, extremely different, conditions. Whereas Mars lost most of its amosphere and evolved toward desertification, Venus probably undergone a runaway greenhouse resulting in a massive atmosphere and a high surface temperature. The absence of liquid water on Mars and Venus, their one-plate tectonic regime, the lack of an intrinsic magnetic field protecting them from solar wind erosion, make them different from Earth. Understanding why they evolved differently, and why Earth didn't follow these two extreme paths, is a major goal of comparative planetology. Different aspects of atmospheric evolution, coupled to interior evolution, will be presented, and replaced in the context of space exploration.
We study long-term instabilities and planet-planet scattering in a system with three giant planets around a central star using numerical experiments. We characterize the growth timescale of instability as a function of the initial orbital configuration. We obtain the final stable configurations and determine their statistical properties from large numbers of integrations. We discuss strong planet-planet scattering as a possible mechanism for producing both highly eccentric orbits and "Hot Jupiters" in the observed extrasolar planet population.
The investigation of the physical mechanisms explaining the observed planet-star metallicity correlation is of particular interest today. Nevertheless,we don´t have a clear idea for this mechanism and we can express this problem this way:is high metallicity the cause of planets or planets the cause of high metallicity ? We investigate the behavior of the metallicity of young coeval associations with different ages in relation with the convective layer´s size of the stellar members. We performed a similar analysis for old main sequence field stars. This will maybe test the possibility of explaining the know observed strong correlation of stars with planets with larger metallicity by means injection of planetesimals during the early stage of evolution.
In Earth sciences, observations from orbit often benefit from "ground truth," but occur only rarely for planetary explorations. Fortunately, orbiter ground-track pixel sizes are decreasing while spectral band content is increasing. Landers are becoming rovers, expanding their vistas by orders of magnitude. With these advances, the challenges of scale are becoming more apparent. The discovery of as many different classes of rock types by MER Spirit rover in a transect across one topographic feature (Husband Hill, area 4 km2) as the total number of compositional units mapped by orbiters over the entire planet (100 million km2 in area) indicates the fundamental dilemma for exploring a complex planet. Aqueous history of Meridiani Planum is revealed by "microscopic imaging" (100 µm pixel size) of bedding patterns. The scale gap inhibits a secure understanding of Mars.
Magnetism is the essential tool of geophysics. An active dynamo tells us about the composition and state of a planet's (satellite's) interior and how it evolved. Crustal remanence gives us a magnetic record of times past, as illustrated by the striped pattern of anomalies associated with sea floor spreading (on Earth and Mars)in the presence of a reversing dynamo. I argue that the Mars Global Surveyor (MGS) mapping observations can be interpreted in the context of plate tectonics. From Mars we travel to the Saturn system, to rings sculpted by an electromagnetic erosion process that to this very day delivers water from the geysers of Enceladus to Saturn's atmosphere.
In this presentation we will review the satellite systems structure and we will try to describe what are the main processes leading to their formation. The satellite formation process cannot be studied independently from will the formation of the central body, and therefore we will describe it in the context of the giant planet formation. There are 2 main groups of satellites: 1- Major Prograde Satellites of Jupiter, Saturn, and Uranus. In this case the role of the central object is extremely important, in fact as the gas giants formed, the pulled in gas and dust due to their gravitational attraction. This material collapsed into a disk in much the same way that the solar nebula did. The inner portion of these disks were possibly warmer due to the heat of the forming planet, so we see similar gradients in composition (rock/ice mix) to those in the solar system as a whole. The process of disk formation and the disk characteristics will be discussed. It will be shown that satellites can be formed in this kind of disk. 2. Captured Satellites Many small outer moons of the gas giants are captured. Aso in this case the thermodinamical characteristics of the gas swirling about the central body could be relevant. The probability of gas capture will be also discussed.
152 extrasolar planetary systems have now been detected by radial velocity(RV), 18 of which are multiple systems. Because of the planets proximity, and large masses and eccentricities (eg. HD202206, GJ876, HD82943), these multiple systems show large chaotic regions and, due to the uncertainties in the observations and in the dynamical models, numerical fits from RV can be largely unstable. On the other hand, stable regions can exist nearby the solution with optimal fit, as for example, in presence of a resonant island. The stable resonant solution, which can be found through dynamical studies and frequency map analysis, should then be preferred to the solution of optimal fit. Combining RV and frequency analysis, we can thus provide stable fits for planetary systems, and also look for possible limits on inclination and masses.
Investigations of Titan's atmospheric composition in the past decade include measurements by ISO (detection of the water vapor in Titan's atmosphere and description of the chemical composition as a disk-average). More recently, data recorded by Cassini/CIRS allow the study of several molecular signatures: hydrocarbons, nitriles and CO2. A firm detection of benzene (C6H6) was provided by CIRS at 674 cm-1, as well as the abundances of the trace constituents and some of their isotopes in Titan's stratosphere. The D/H ratio on Titan was determined from the CH3D band at 8.6 micron to be 1.25 ±0.2 ×10-4. Information is retrieved on the meridional variations of the trace constituents and tied to predictions by dynamical-photochemical models.
Traditionally, comets are suspected to come from two "reservoirs": the Oort cloud and the Kuiper belt. The two kinds of comets formed at different places in the primitive Solar System and experienced different orbital evolutions. One can thus expect different chemical and physical properties. I will review which differences are effectively observed or expected: chemical and isotopic compositions, spin temperatures, dust particle properties, nucleus surface properties... The difficulty of such a study is that long-period comets from the Oort cloud are better known, from Earth-based observations, than the weak short-period comets from the Kuiper belt. On the other hand, only the latter are easily accessed by space missions.
Comets and asteroids are rich in complex molecules inherited from the parent interstellar cloud, synthesized in the solar nebula, or produced in the body itself. These molecules may have contributed, together with chemical synthesis in the early atmosphere and ocean, to the initial stock of prebiotic molecules from which Life has started. To precise what has been their exact role is an important question for astrobiology, and a source of challenges for astronomers, planetary scientists and chemists. We will present the concept of prebiotic molecule, the nature and possible origin of the organic molecules present in Solar system small bodies and in the Interstellar medium, the questions posed by a quantitative estimate, and some examples of progress we may expect in the future.
I will summarize the results of recent modelling of dust growth and settling in protoplanetary disks. For the first time now, such calculations have been coupled with full radiative transfer to show the observational effects of dust evolution in disks. These calculations show how dust coagulation leads to a fast depletion of small grains in the solar nebula, with severe consequences for the structure and appearance of the solar nebula. I will also show results of modelling the emission of the H2D+ molecule, a recently discovered tracer of cold gas and ionization in disks that may become a major tool in the future for tracing the gas component in protoplanetary disks. In this way it will finaly be possible to study the evolution of both gas and dust in disks.
Cassini magnetometer observations from three targeted flybys of Saturn's icy moon Enceladus have revealed the existence of a dynamic atmosphere. This unexpected detection was originally made on a distant flyby and was subsequently confirmed on two follow-on flybys one of which was very close, at a distance of 173km from the surface of the moon. The magnetic field observations from all three flybys will be described as well as their interpretation. The observations from the second and third flybys are consistent with an atmospheric plume concentrated near Enceladus's south pole.
Solar wind induced escape is one of the effective mechanisms responsible for atmospheric and ionospheric losses on Mars. ASPERA-3 observations carried out on the MEX spacecraft reveal the efficient extraction and energization of planetary ions. Planetary ions (O+, O2+, CO2+) gain energy of several keV on a distance of several thousands km from the planet. It is found that processes of ion extraction and penetration of solar wind plasma into the Martian magnetosphere are closely related. Morphology of ion fluxes, role of crustal fields and mechanisms of extractions are discussed.
The correlation between specific meteorites and asteroids is a long-standing problem. The best-known correlation seems to be the HEDVesta, although several problems still remain to be solved. A number of small asteroids exist with the same spectral characteristics as (4) Vesta, and are taxonomically classified as V-type, as Vesta. These small asteroids are mostly found in the region near Vesta, but some are also in near-Earth orbits, and one is in the outer part of the main belt. The purpose of this work is try to determine if the HED meteorites found on Earth and the small V-type asteroids are all genetically linked to Vesta through the comparative study of their mineralogy. We report the spectral reflectance analysis, 0.4-2.5 microns, of 47 basaltic achondrite meteorites and 22 V-type asteroids trying to associate spectral properties with mineralogy. The meteorite spectra are from 25 eucrites, 13 howardites and 9 diogenites, taken from the RELAB database. On the other han! d, the spectra of 18 main belt asteroids and 4 NEOS were observed in different instruments/telescopes. We used the Modified Gaussian Model to fit the spectra to a serie of overlapping, modified gaussian absorptions. The fitted individual bands are validated against established laboratory calibrations. With spectral resolution extending to the near-infrared, we are able to resolve the presence of both high-calcium pyroxene (HCP) and low-calcium pyroxene (LCP) and, thus, use the HCP/(HCP+LCP) ratios to remotely trace igneous processing on asteroids. A search of this mineral provides a useful probe of differentiation.The high HCP/(HCP+LCP) ratios found require extensive differentiation of these asteroids and/or their primordial parent body. The degree of melting obtained for the eucrites, using the former ratio, is comparable with that obtained for all the V-type asteroids here analyzed, suggesting a comparable geologic history.
Reflectance spectra of HED meteorites have been convolved with the response curve of the framing camera (FC) filters to obtain the expected response of the camera to the surface material of Vesta. Several spectral parameters were analyzed to obtain mineralogical information. Two framing cameras (FC) onboard the DAWN mission, designed and built by the MPI for Solar System Research in co-operation with DLR Berlin and IDA Braunschweig will provide images of the surface of asteroids (4) Vesta and (1) Ceres. The field of view of 5& # 9702;×5& # 9702; is imaged onto a frame-transfer CCD with 1024×1024 sensitive pixels. The FC will provide a high spatial resolution images of the surface of Vesta in 8 filter, one clear and 7 band pass filters in the visible/NIR range of the spectrum (430, 540, 650, 750, 830, 920 and 980 nm).
The TEXES instrument, mounted at the NASA/IRTF, has been used to map H2O2 and H2O on Mars (Encrenaz et al., Icarus 170, 424, 2004; Icarus 179, 43, 2005a). While the H2O map appears in good agreement with the GCM and previous measurements, there are some departures between the H2O2 maps and the GCM predictions. Heterogeneous chemistry may help resolving the discrepancies (Lefèvre et al., 2nd Mars workshop, Granada, 2006).
OMEGA/MEx has also been used to map H2O over the seasonal cycle (Encrenaz et al., A& A 441, L9, 2005b; Melchiorri et al., submitted to PSS, 2006). Results appear in general agreement with
the GCM and TES previous results. OMEGA has also been used to study the CO mixing ratio over Hellas as a function of solar longitude. An enhancement by 2 to 3 is observed during southern winter, in global agreement with the GCM predictions (Forget et al., 2nd Mars workshop, Granada, 2006).
The Cassini mission is opening a new era in the exploration of Saturn's rings, in the quest for answers on still pending issues on their origin and evolution:
Undoubtedly the power of the mission resides in the diversity of its viewing points,
This talk will review recent news from the peaceful armada.
We present model atmospheres of several hot Jupiters and compare our computed infrared spectra to recent Spitzer Space Telescope and ground-based infrared observations. One-dimensional radiative-equilibrium models yield infrared planet-to-star flux ratios that are in general a good match with the data published to date. We also explore spectra as a function of orbital phase for a three-dimensional dynamical model of planet HD209458b. The day-side temperature structure of the dynamical model, and therefore the resulting spectra, is quite different than other models published to date and leads to excellent agreement with observations. We disuss prospects for observing temperature contrasts as a function of orbital phase.
The study of the giant planets chemical composition can be decoupled in two different part, the stratospheric composition and the tropospheric composition.
The tropospheric global chemical composition of the giant planets is mainly determined by their formation scenario. Any difference with the solar composition signals a enrichment or depletion process that may provide insights to what happened in the solar nebula 4.6 Gyr ago. Unfortunately, the most interesting species, methane, ammonia, hydrogen sulfide and water do condense in the giant planets tropospheres (methane only for Uranus and Neptune), deeper and deeper as we go further out from the Sun. Therefore, spectroscopic remote sensing provides only partial information on the tropospheric composition, and other techniques have to be used, such as gravimetric or in situ methods. I will review our current knowledge obtained from in situ, gravimetric and spectroscopic methods. This knowledge does not always allow us to discriminate between the various formation models that propose an heavy element source either in the form of tar, amorphous ice or clathrates.
In the shallow troposphere, chemical and dynamical processes do affect the chemical composition and produce vertical and horizontal heterogeneities. Measuring humidity in the condensable species provides clues to observe the giant planets meteorology and to understand the dynamics of these extremely deep atmospheres. I will in particular review the compositional evidence for the shallow or deep rooted models of Jupiter's belt and zone structure. Dynamics can also bring up to the upper troposphere some chemical species only thermodynamically stable in the deep atmosphere. This help us to constrain both the deep chemical abundance and the overturning timescale of these giants.
In the stratosphere, the chemistry is dominated by the photolysis of methane and the subsequent production of heavier hydrocarbons. As any solar-driven processes, it mainly takes place at the homopause level, and at the subsolar point. Then the products are redistributed to the whole stratosphere through vertical and horizontal turbulent mixing or advection. Hence, the stratospheric chemistry constitutes an efficient tracer of the stratospheric dynamics. In the stratosphere, the fall of kilometer-sized comets, IDPs, or ring and satellites sputtered particles, also affect the chemistry, in particular the oxygen chemistry that would otherwise not exist.
Recently, the stratospheric chemistry have seen some important progresses, with the detection of C2H4 in Jupiter, Saturn and Neptune, C2H6 in Uranus, C3H8 in Saturn, CH3C2H in Jupiter, Saturn and Uranus, C4H2 in Jupiter and Saturn, and C6H6 in Jupiter and Saturn. Moreover, meridional variations in the abundance of C2H6 and C2H2 have been measured in Jupiter and Saturn, leading to 3D study of the coupling between stratospheric chemistry and dynamics. The external products detected in the stratosphere of the giant planets, for example H2O, CO, CO2 and HCN in Jupiter, can also reveal interesting details of the stratospheric circulation. Our understanding on the origin of the Oxygen external flux to the giant planets has also advanced, with the detection of CO in Uranus, the evidence for an impact of a kilometer-sized comet every century on Jupiter, and the possible evidence for a recent cometary impact on Neptune.
The Huygens Atmospheric Structure Instrument (HASI) is a multi sensor package which has been designed to measure the physical quantities characterizing Titan's atmosphere during the Huygens entry and descent phases and at the surface. HASI's suite of sensors measured the physical and electrical properties of Titan's atmosphere. Profiles of temperature, pressure, density, atmospheric conductivity have been collected. HASI investigated the electric properties and the nature of the surface. Accelerometers measured deceleration in all three axes as the probe was in the entry phase. With the aerodynamic properties of the probe already known, it has been possible to determine the density of Titan's high atmosphere and to deduce temperature and pressure profiles. During the descent (from 162 km down to the surface), temperature and pressure of the atmosphere were measured directly and the Permittivity and Wave Analyzer sensors measured the electron and ion conductivities as well as the complex permittivity of the atmosphere and searched for electric wave activity including lightning. Acoustic signals collected by the HASI microphone were processed by the on board FFT and their amplitude and main frequency, avera! ged over two minutes, were transmitted to the ground. HASI provided, in addition to its own scientific data, calibration information of use by other instruments on Huygens and by remote sensing observations from the Cassini orbiter.
The analysis of the composition of the atmospheres of Satyrn and Titan measured by the Cassini-Huygens mission has been interpreted by Hersant et al; (2006). Observations suggest that volatiles which formed Titan wrte trapped by clathration at low temperature in the late solar nebula in the region of the formation of the Saturn system. Especially, the detection of 36Ar in the atmosphere of Titan by the GCMS aboard Huygens implies that this gas was initially trapped by clathration. The composition of the Enceladus plume measured by the INMS instrument aboard the Cassini spacecraft (Waite et al;, 2006) is consistent with the analysis of Hersant et al (2005), assuming that NH3 has been converted into N2 in the interior of Enceladus.
References : Hersant et al. (2006), submitted to Icarus. Waite et al. (2006), Science, 311,1419-1422
Sulphates and associated oxide deposits, detected by the OMEGA instrument, bring compelling information about the amount and form of water on Mars in its early history. We will describe the factors influencing sulfate detection, and the constraints that we can obtain about the absolute amount of sulfate. We will describe how particular deposits and stratigraphy relationships allow us to constrain the time of sulfate formation as well as the past geological contexts. Relationships with altimetry indicate that diagenetic processes might have played an important role in mineral transformation.
On its tour through the Saturn system Cassini has acquired hundreds of images of the Saturn satellites with resolutions much improved over the earlier Voyager data. These new images provide multi-spectral information on the surfaces but also multi-stereo coverage that can be used for high-resolution topographic modeling of the satellites. In this talk topographic models of Phoebe, Iapetus, Dione, and Tethys will be presented and implications for formational processes will be discussed.
We will review the most recent data on short-lived radionuclides (Fe-60, Cl-36, Be-7) and discuss the implications for the origin of our solar system. We will specifically discuss irradiation processes in the solar accretion disk and the astrophysical context of our sun's birth.
Tectonic and volcanic structures are observed on several moons of the jovian and the saturnian systems. Understanding the origin and the principles of such activities require both theoretical and experimental constraints on the dynamics of thick icy mantles. Physical parameters of the ice material strongly depend on pressure, temperature, and composition of ices. Since ices of the outer system are placed under extreme conditions, specific experimental studies have been set up these last 20 years for planetology purposes. A review of the different experiments which have provided valuable information for studying icy moons will be proposed. The importance of this approach for planetology will be illustrated in the case of the putative cryovolcanism on Titan. In particular, the problem of the methane replenishment in the atmosphere will be addressed.
Titan's surface intimately affects the composition of the troposphere through the evaporation and possible outgassing of methane. Likewise Titan's troposphere affects the composition of the surface through methane rain and the sedimentation of ethane, acetylene, and haze; that is, photochemical byproducts of methane photolysis in the stratosphere. The Cassini Huygens mission has provided us with a partial understanding of these processes. Here I will discuss Titan's methane cycle in light of Cassini measurements of Titan's methane humidity, cloud structure, and various surface features, as well as current models of the dynamics of Titan's atmosphere, presented in some of the contributed talks. The talk will conclude with a series of questions that point to the enigmatic nature of the moon, and our still early understanding of its ways.
On 4 July, Deep Impact delivered 19-GJoule of kinetic energy to the nucleus of comet Tempel 1, taking numerous images and spectra of the comet before, during and after impact. The preliminary analysis of the data has already lead to significant, new understanding of cometary properties and behaviour (A'Hearn et al., 2005, Science 310). This talk will summarize the present state of our understanding.
A dust astronomy mission aims at the simultaneous measurement of the origin and the chemical composition of individual dust grains in space. By distinguishing interstellar from interplanetary dust of cometary or asteroidal origin based on their trajectories and comparing their composition important clues on processes in the early solar system can be obtained. The dust observatory mission "Cosmic DUNE" has been defined to reach this goal with newly developed dust instrumentation. A dust trajectory sensor has been developed which is capable of obtaining precision trajectories of sub-micron sized particles in space. A new high mass resolution dust analyzer of 0.1 m2 impact area can cope with the low fluxes expected in interplanetary space. With these instruments both novel dust measurements in low-Earth orbit and improved dust collection and sample return schemes are achievable.
A young hot Jupiter with a modest eccentricity (<=0.2) at 0.04-0.05 AU around a solar-type star can be tidally heated and be inflated to its Roche radius. Consequently the planet loses its mass through the Roche-lobe overflow and migrates outwards. With a high initial eccentricity (>0.2), we show that a hot Jupiter can lose its gaseous envelope and move to 0.1 AU or beyond. We suggest that the remaining core of a young hot Jupiter via this catastrophic process is the hot Neptunes that we see today around G dwarfs.
We now know of thirteen giant planets for which we have measurements of both the mass and the radius. For four of them, we also have additional constraints provided by the gravitational moments J2 and J4 and atmospheric measurements of the temperature and composition. I will compare the interiors of these planets according to present knowledge and show that all of them can be thought to belong to a unified ensemble mostly determined by the composition of the protoplanetary disk from which they were born.
One of Cassini's most exciting discoveries is that Saturn's moon Enceladus is erupting water vapour and ice. The plume of particles and vapour spewing from the south pole reaches an extent almost equal to the diameter of Enceladus itself. This water feeds the E ring and supplies molecules to the Saturnian system. Neutral water products (OH, H, O) fill the system, influencing the dynamics of the magnetosphere. Remote sensing of these water products may be useful for determining the variability of Enceladus' eruptive activity. Each of Cassini's instruments played an important role in understanding the processes playing out on Enceladus. This talk will review key contributions of each, summarize our current state of knowledge, and describe plans for future observations.
The Io-Jupiter interaction is at the origin of intense decametric radio emissions. Some of these emissions, the short (or S-) bursts, are discrete emissions near the local cyclotron frequency, drifting in the time-frequency plane. They are thought to be cyclotron-maser emissions by electron "beams" moving adiabatically along the magnetic field lines. These electrons have been accelerated toward Jupiter, and reflected by magnetic mirror effect near the planet. upgoing electrons have an unstable loss-cone or shell distribution and are thus able to emit waves
An automated analysis of 230 dynamic spectra allows us to confirm this model over 5.106 drift rate measurements. A typical energy of 4 keV for the emitting electrons is deduced from observations. Moreover, electric potential drops of nearly 1 kV are observed in more than 15
Using the former results as inputs, we simulate electron distributions along the Io flux tube in order to investigate the emission mechanism. Different models of electron acceleration and free energy sources are tested and compared with the observational results.
Titan, the largest satellite of Saturn, is believed to harbour an internal water ocean that is likely to be enriched in ammonia and overlain by an outer ice shell of about 70 km thickness. Furthermore, the outer shell is subject to deformation with a period of about 16 days due to tidal forces exerted by Saturn. Depending on the thermal and orbital states (mainly eccentricity and semi-major axis), orbital energy is dissipated in the ice shell because of anelastic contributions to tidally-induced deformations on characteristic time scales of several days to weeks. As a consequence, Titan's orbital eccentricity will be damped over time and must be expected to have been considerably higher in the past. This poses a severe problem because of the relatively high present-day value of Titan's orbital eccentricity of 0.0292. Taking, for the sake of simplicity, the present-day tidal dissipation rates fixed over the age of the solar system would lead to such high initial eccentricities that gravitational perturbations of Titan on its neighboring satellites would be too strong to keep them in stable orbits about Saturn. The dependence of Titan's dissipation rate on its thermal state and on the ice thickness may offer an explanation. Dissipation rates are expected to have been considerably smaller in the early phase of Titan's history, because the thickness of an ice shell capable of transferring the then higher radiogenic heat flow to the surface should have been much smaller. As a consequence, thin-shell dissipation rates would have been much lower due to the smaller volume of the ice shell. With increasing thickness of the ice layer in the course of the satellite's cooling history, however, the tidal dissipation rate will also increase thereby causing a general reduction of the orbital eccentricity. The onset of thermal convection may be crucial in such a scenario because it would keep a large part of the ice shell at a relatively high temperature. We compare different tidal evolution models of Titan by varying the bulk ammonia content of the water-ice/liquid shell. Depending on the concentration of ammonia, a significant melting point reduction of the satellite's water-ice liquid shell is expected. This would have consequences for the shape of the radial temperature profile with important implications for the internal dissipation of tidal energy and Titan's orbital evolution.
Detection of many extrasolar planets has stimulated us to make a systematic study of planet formation. Theoretical studies on the accretion and dynamical evolution of planets have constrained the masses and periods of planets in extrasolar systems. From an astrobiological point of view, special attention has been paid to probabilities of the existence of planets in the habitable zone where a planet can keep liquid water above its surface. Few studies have, however, discussed how likely a planet acquires a sufficient amount of water. Although there are several sources of water on terrestrial planets, we focus on an idea that water is produced on a planet by oxidation of a hydrogen-rich atmosphere, the nebular gas being attracted gravitationally by the planet. The process of water production could work if a planet captures a sufficient amount of hydrogen, has a molten surface (i.e., magma oceans), and contains some oxide. Our extensive investigation of properties of the hydrog! en-rich atmosphere shows the former two conditions are fulfilled on an Earth-size planet for a wide range of parameters. Moreover, some oxide such as FeO is common material in planets, as long as the C/O ratio of extrasolar systems is less than unity. Therefore, sufficient water on an Earth-sized rocky planet is a natural consequence of planet formation. The range of masses of those potentially-habitable planets is also constrained.
The ROSINA (Rosetta Orbiter Spectrometer for Ion and Neutral Analysis) instruments, mounted onboard the Rosetta probe, comprises two mass spectrometers and a pressure sensor. The two mass spectrometers complement one another and have two basic operation modes. The first mode is for analyzing the cometary neutral gas and the second one for the direct measurements of the cometary ions. ROSINA is designed to analyse the volatile material in the vicinity of comet Churyumov-Gerasimenko (CG) and to quantify the molecular and isotopic composition of CG during the conjoint journey towards the Sun. We will present neutral gas measurements from commissioning in space and ion measurements that were performed with a low energy ion source in the lab.
The solar wind is representative for the isotopic composition of the early solar nebula and therefore a reference for isotopic fractionation processes that occured during the formation of planets. An updated value for the isotopic composition of nitrogen measured by the CELIAS/MTOF sensor on board SOHO is given and discussed in the context of models of the protoplanetary disc.
Earth's atmosphere and climate have both undergone marked changes during the course of Earth's history. A dimmer sun in the past was likely offset by enhanced greenhouse gas concentrations in Earth's atmosphere. CO2 and H2O were probably the dominant greenhouse gases initially, but CH4 may have become an important contributor soon after life evolved. CH4 is mostly biological in origin; hence, life may have played a direct role in controlling climate on the early Earth. The rise of O2 at 2.3 Ga, now conclusively established by studies of mass independent fractionation (MIF) in S isotopes from ancient rocks, caused a marked decrease in methane, thereby triggering the Paleoproterozoic glaciations. An earlier, less well documented glaciation at 2.8-2.9 Ga corresponds to a second anomaly in the MIF record and may also have been triggered by biological innovations.
The stability of thin films of two amino acids against UV irradiation, under different simulated martian surface conditions, has been investigated. The data obtained through these experiments are used to predict the survival time of these compounds on the martian surface. Thin films of glycine and alanine are expected to have a half-life of 22 hours and of 4 hours, respectively, when irradiated with Mars-like UV flux levels. In these results no effects of temperature or a CO2-atmosphere have been taken into account. In follow-up experiments the effects of a CO2 atmosphere and low temperature on the destruction rate of glycine when irradiated with Mars-like UV radiation have been measured. The results showed that the presence of a 7 mbar CO2 atmosphere does not affect the destruction rate of glycine and that cooling the sample to 210 K lowers the destruction rate.
Models of the radiation transfer of Titan's atmosphere based on observations of the DISR instrument onboard the Huygens probe are used to calculate the illumination conditions of the surface near the landing site. Topography leads to variations of the surface brightness that are comparable to the contrast of observed features without invoking changes of the albedo. To make quantitative models the scattering properties of the surface (bidirectional redistribution function BRDF) have to be derived. DISR observations (mainly of the IR spectrometer) are used to determine the BRDF over a restricted range of scattering angles.
The areosols (tholins) in Titan's atmosphere control its scattering properties. DISR (Cassini/Huygens) observations show that large monomer clusters with more than 500 particles seem to be required to match the intensity as function of altitude and scattering angle. The atmosphere shows a back scattering peak that is not prominent for most large clusters. Systematic investigations (model calculations) varying also the structures of the clusters will be presented. Polarisation is also considered.
Occultation survey is currently the only way available to detect small trans-Neptunian objects (TNOs) with a size of a few kilometers or smaller. The status of TAOS (Taiwan-America Occultation Survey) project is reported. In order to monitor thousands of stars in the same field at a time scale of a fraction of a second using CCD camera with multiple telescopes, a novel method (software) applied to CCD readout, namely, zipper mode operation was tested recently. We are also looking for occultation signal in X-ray data. For a single target observation to be compatible with the TAOS result, we expect an increase in the event rate according to the (unknown) size distribution of TNOs at the faint-end. A shorter sampling time is required to detect a smaller shadow. RXTE observation on a bright, steady, point-like source such as Sco X-1 was selected as an example. A detail study in diffraction pattern might provide the
possibility to probe kilometer size object as far as the Oort cloud, or, to resolve the X-ray source itself down to a micro-arcsec resolution.
The wave planetology states that principal structures of celestial bodies are made by warping waves . Orbits make structures. It means that as all bodies move in orbits with changing accelerations they all are subjected to an action of inertia-gravity waves. In rotating bodies these waves have 4 directions: ortho- and diagonal. An interference produces risen and fallen blocks. There is an inverse relation between orbital frequencies and their sizes: higher frequency-smaller blocks. I.g., Mercury ðR/16, Venus ðR/6, Earth ðR/4, Mars ðR/2. Along with this, in all bodies invariably develops the longest warping wave-the fundamental wawe1 long 2ðR (R-a body radius). This wave is responsible for dichotomy: an opposition of convex and concave hemispheres. Established in terrestrial planets now with help of Cassini it is seen in all saturnian as before in all Galilean satellites.
The results of the Mars Exploration Rover mission provide clear evidence for past sedimentary processes. The mineral assemblage of sulfate rock deposits comprises Mg- and Ca-sulfates along with jarosite, indicating acid-sulfate weathering of basaltic materials and subsequent evaporation of brines and diagenesis. Our analysis of chemical data returned from Mars missions confirms the global involvement of acid-sulfate weathering in the formation pathway of weathering crusts, soils and sedimentary rock deposits. The observed chemical variability is analyzed by means of principal component analysis in order to describe chemical alteration in terms of alteration vectors that link the compositions of fresh rocks and their weathering crusts.
This work is intended to investigate the influence of temperature dependent metamorphism of ice on the shape of small depressions in the surface of cometary nuclei. We are mainly interested in the role of initial cohesivty of a nucleus. For this purpose we simulate sublimation of ice from the facets of initially cylindrical depressions in ice of different initial structure. The simulations account for the diurnal and orbital changes of insolation and its dependence on the current shape of the depressions. Our model includes heat transport in the cometary material and metamorphism of ice. We present the results obtained for the nucleus of the comet 67P/Churyumov-Gerasimenko, target of the ESA cornerstone mission Rosetta.
The Radio Plasma and Wave Science experiment of the Cassini spacecraft allows to observe quasi-continuously the auroral Kilometric Radiation from Saturn (hereafter SKR). In order to identify SKR components and use them to study questions such as the rotation period of Saturn, moons-magnetosphere interactions, the magnetic field anomaly, we build long-term, homogeneous, calibrated and normalized SKR time series and dynamic spectra from Cassini's rich but heterogeneous data set. To do so, we take advantage of Cassini-RPWS goniopolarimetric capability, which allows to measure the polarization and k-vector of incoming radio waves. First results are presented which include the global spectrum of northern and southern SKR, its variations versus time, latitude and local time, the tentative identification of sub-components, and comparison with Voyager results. Then we perform a Fourier analysis of SKR time series in selected frequency bands in order to adress the rotation period of Saturn, possible high latitude magnetic field anomalies, and SKR control by moons.
Mars Global Surveyor MAG-ER experiment has detected strong and localized magnetic anomalies on Mars. These anomalies are of lithospheric origin, and the magnetization very likely is related to an ancient active (Earth-like) magnetic dynamo. On the Earth, paleomagnetic studies on samples are performed to better characterize the past behavior of the geodynamo, assuming that the magnetic and rotation poles are identical over long time period. The case for Mars is different as one has to rely on remote measurements. However, paleomagnetic approaches may be used, giving some clues to possible ancient polar wander. Many studies have shown a cluster of paleopoles near Tharsis area, suggesting a different magnetic (and rotation) pole. A new result comes from a magnetic anomaly associated with a volcanic construct, Apollinaris Patera. This volcano probably witnessed the latest stages of the dynamo, before it shut down. The anomaly associated with this edifice indicates a polar magnetic paleopole. This would mean that a major polar wander took place before the dynamo stopped on Mars.
The understanding of Titan's atmospheric and surface properties depends significantly on our knowledge of the formation, structure and optical properties of the main haze structures observed, and which are believed to be the product of the complex organic photochemistry that takes place in the satellite's thick atmosphere. In this paper, we investigate the possible pathways which lead to the formation of the haze particles from the gas molecules of the atmosphere.
The gas-particle transformation in Titan's atmosphere is simulated by means of a coupled radiation transfer photochemistry microphysics model in one dimension in a self-consistent scheme. The atmospheric model extends from the surface up to the lower thermosphere and incorporates: high resolution radiation transfer codes for solar and thermal radiation, complete neutral species photochemical evolution and a detailed Eulerian description of the microphysical haze particle growth.
Laboratory experiments for the haze formation pathways and previous theoretical studies on this subject, suggest that the chemical structure of the aerosols includes polymers of acetylene, nitriles, benzene, polyaromatics, and copolymers of these. We have also extended the possible pathways by including the nitrogen-containing heterocycles and methylenimine copolymers. The latest results from the Huygens probe's ACP instrument have provided some insight into the processes, with a clear indication of nitrogen incorporation in the aerosol's structure and a homogeneous composition for altitudes between 20 and 130 km, which suggests a common chemical source for the haze monomers at higher altitude layers.
We validate different chemical pathways for particle formation by comparing the derived chemical composition, temperature structure and geometric albedo with observed values. According to our results, the vertical profile for the production of haze monomers from the suggested pathways, have a strong dependence on the reactions chosen: pure hydrocarbon polymers are mainly produced in the lower stratosphere while nitrile and aromatic polymers contribute mainly at high altitudes. The position of the production peak affects significantly the position of the stratopause and the overall temperature structure.
The role of the atmospheric escape has been particularly debated in the frame of the study of Mars' history. It is among the processes which may explain the evolution of Mars' atmosphere from a significantly thick atmosphere during (a) short episode(s) at the end of the Noachian to its present 6 mbar state. In the case of Titan's atmosphere, atmospheric escape may deeply influence its present composition. More generally, atmospheric escape permanently shapes the immediate environment of a planetary object and changes the interaction of this object with the solar or magnetospheric plasma. Among the most dramatic illustration of such an influence, the thin atmospheres of Europa and Io have been identified as the main sources of neutral and ionized species in the Jovian internal magnetosphere. Both satellites lose a significant part of their atmosphere which forms two tori of neutral and ionized particles shaping Jupiter magnetosphere. For most of these planetary objects, thes! e atmospheres may have reached an equilibrium between escape and any mechanism leading to their enrichment.
The mechanisms leading to atmospheric escape depend on the presence of an internal magnetosphere or of a remanent magnetic field, on the radiative environment, on the upper atmosphere chemistry and on the capability of a planet or satellite to permanently replenish its atmosphere. They also depend strongly on the solar activity and therefore should have significantly evolved during the early age of the solar system.
Unfortunately, there are only few markers of a past atmospheric escape remaining in the present atmospheres. Therefore, our knowledge of the evolution of the atmospheric escape in the past solar system is essentially derived from models applied to the present state and extrapolated to the past.
The main sources of uncertainty on Mars' past atmospheric escape is in this sense very illustrative of how could progress our understanding of the evolution of the Martian atmosphere. Actually any progress on that matter would help us to better understand the main processes leading to the disappearance of an atmosphere of a terrestrial planet like Mars and not of the atmosphere of terrestrial planets like Venus or the Earth.
Results concerning several series of impacts experiments are presented: (i) H2O-ice impactors on H2O-ice targets or on H2O-ice & # 8211; mineral targets, (ii) Plastic or metallic impactors on H2O-ice targets and on CO2-ice targets, (iii) H2O-ice impactors on the H2O-ice & # 8211; CO2-ice & # 8211; silicate powder targets (pre-heated from the surface to introduce thermal stratification of the components). The applied impactor velocities were from the range 100 & # 8211; 800 m/s or they were about 5 km/s. The porosities of the targets were near zero (H2O-ice and CO2-ice blocks) or they varied in large intervals. Experiments were aimed for studies: (j) Morphology of the craters in the different types of targets, (jj) Specific energy of the break-up thresholds, and (jjj) Impact disruption of the small bodies of the Solar System.
The largest impact craters observed on small satellites and on asteroids are considered. The available data are for 13 satellites and for 8 asteroids (10 icy bodies and 11 rocky bodies). The craters are considered as near-sub-catastrophic. The critical ratio (crater diameter D)/(target radius R) divides cratering regime from shuttering regime. In the model of impact break-up gravitational energy, strength energy, and surface energy are considered. The specific energy of break up is found to be Q(R)=a+bR2+cR-1. The coefficients a,b,c are discussed both for icy and for rocky targets. Impactor velocity corresponding to cratering/shuttering limit is discussed versus impactor/target mass ratio. Results are applied for discussion of catastrophic collisions in the different regions of the Solar System.
We sum up low and high resolution climate simulations made with the 3D LMD Global Climate Model designed to simulate the present-day Mars water cycle, but using different obliquities and orbital parameters.
Predictions of the climate model shows that, as on Earth, recent variations in rotational and orbital parameters of Mars over the last 10 Myr may explain the formation of many amazonian icy landforms: mid-latitude and tropical glaciers, ice mantling in high-latitudes and northern polar layered deposits without the involvement of subsurface reservoirs(Levrard et al., Nature, 2004, Forget et al., Science, 2006, Levrard et al., 2006, in preparation).
The observed properties of giant planets, models of their evolution and observations of protoplanetary disks provide constraints on the formation of gas giant planets. The four largest planets in our Solar System contain considerable quantities of hydrogen and helium, which could not have condensed into solid planetesimals within the protoplanetary disk. All three (transiting) extrasolar giant planets with well determined masses and radii also must contain substantial amounts of these light gases. Jupiter and Saturn are mostly hydrogen and helium, but have larger abundances of heavier elements than does the Sun. Neptune and Uranus are primarily composed of heavier elements. HD 149026 b, which is slightly more massive than is Saturn, appears to have comparable quantities of light gases and heavy elements. HD 209458 b and TrES-1 are primarily hydrogen and helium, but may contain supersolar abundances of heavy elements. Spacecraft flybys and observations of satellite orbi! ts provide estimates of the gravitational moments of the giant planets in our Solar System, which in turn provide information on the internal distribution of matter within Jupiter, Saturn, Uranus and Neptune. Atmospheric thermal structure and heat flow measurements constrain the interior temperatures of planets. Internal processes may cause giant planets to become more compositionally differentiated or alternatively more homogeneous; high-pressure laboratory experiments provide data useful for modeling these processes.
The preponderance of evidence supports the core nucleated gas accretion model. According to this model, giant planets begin their growth by the accumulation of small solid bodies, as do terrestrial planets. However, unlike terrestrial planets, the growing giant planet cores become massive enough that they are able to accumulate substantial amounts of gas before the protoplanetary disk dissipates. The primary questions regarding the core nucleated growth model is under what conditions planets with small cores/total heavy element abundances can accrete gaseous envelopes within the lifetimes of gaseous protoplanetary disks.
Titan is being revealed as a new world of outstanding scientific richness. After the inscrutable bright and dark near-IR patterns from Earth-based observations, Cassini data suggest impact and cryovolcanism have shaped Titan's surface. Images from the Huygens probe showed a familiar landscape modified by fluvial processes, and the probe has also indicated the mechanical, dielectric and thermal properties of Titan's surface.
A global circulation model suggests Titan's equatorial regions should be dry, while high latitudes are saturated. The detection by Cassini RADAR of sand dunes near the equator, and an apparent coastline at high latitude, are consistent with this picture. Titan's seems very active, and every bit as varied as Earth and begs further multidisciplinary exploration.
The process of disk formation is a universal one in the cosmos, with a variety of different objects exhibiting such structures. Protoplanetary disks are implicitly those whose end-state of evolution is the formation of planets. The protoplanetary disk from which our solar system formed has left a variety of chemical evidence in the form of meteorites, interstellar dust particles, comets, the giant planet atmospheres, and to some extent the atmospheres and bulk compositions of the terrestrial planets and large moons. Our protoplanetary disk was possessed of a strong temperature gradient sustained initially by gravitational and magnetic torques, later by dissipation associated with turbulent viscosity, and finally (in the debris disk stage) insolation. Key chemical dividing points in the disk, all time-variable in their distance from the center, were the thermo-chemically active zone, silicate-condensation line, and the water-ice (snow-) line. In addition, sulfur chemistry wit! h various metallic elements exhibited a strong dependence on time and on the oxidation state of the disk. Jupiter-stimulated radial mixing of large bodies during terrestrial planet formation paradoxically brought water- and volatile-bearing bodies from beyond 1 AU to the Earth, yet preserved a chemical stratification in the asteroid belt. In the end, the system of planets and small bodies formed from the disk is far from chemically homogenized, yet is not a simple reflection of distance-from-center in the protoplanetary disk. As for any high-dimensionality system with access to a large amount of (thermodynamically-free) energy, the result of the evolution of the protoplanetary disk is a highly structured- but in many ways stochasticproduct.
The Huygens probe completed its spectacularly successful mission in January 2005 and the Cassini Orbiter is roughly halfway through its four-year prime mission touring the Saturn system. Prior to the arrival of these international spacecraft, the source of methane in Titan's chemically- and meteorologically-active atmosphere, the origin of that atmosphere, and the astrobiological potential of Titan were the principal mysteries of this planet-sized moon of Saturn. Huygens discovered rain-fed and spring-fed channels in icy highlands grading down into pebbly plains soaked in methane and ethane. It measured key isotopic ratios of primary elements and noble gases that constrain the original molecular carriers of the nitrogen- and carbon- containing atmosphere, and the extent of outgassing (therefore, geologic activity) over time. Cassini's radar discovered volcanic edifices, networks of channels stretching across smooth and rough plains, mountains, and craters; its near-infrared mapper has begun to trace varying compositions across a complex jumble of different terrains. Titan has become a world with a readable history, but what is happening to organic deposits on and within its surface remains to be divined.
The Huygens probe completed its spectacularly successful mission in January 2005 and the Cassini Orbiter is roughly halfway through its four-year prime mission touring the Saturn system. Prior to the arrival of these international spacecraft, the source of methane in Titans chemically- and meteorologically-active atmosphere, the origin of that atmosphere, and the astrobiological potential of Titan were the principal mysteries of this planet-sized moon of Saturn. Huygens discovered rain-fed and spring-fed channels in icy highlands grading down into pebbly plains soaked in methane and ethane. It measured key isotopic ratios of primary elements and noble gases that constrain the original molecular carriers of the nitrogen- and carbon- containing atmosphere, and the extent of outgassing (therefore, geologic activity) over time. Cassinis radar discovered volcanic edifices, networks of channels stretching across smooth and rough plains, mountains, and craters; its near-infrared mapper has begun to trace varying compositions across a complex jumble of different terrains. Titan has become a world with a readable history, but what is happening to organic deposits on and within its surface remains to be divined.
A myriad of bodies orbit beyond Neptune representing the remnants left after planetary formation. These transneptunian objects (TNOs) offer important clues on the origin and evolution of the solar system. We investigate the dynamical properties of all currently known TNOs by performing computer simulations plus tens to hundreds of clones totaling several thousands of particles. We identified TNOs locked in resonance with Neptune in the transneptunian belt (Kuiper belt) and in the scattered disk. Occupied resonances sorted by distance from the Sun are: 1:1 (Neptune trojans), 5:4, 4:3, 11:8, 3:2, 18:11, 5:3, 12:7, 19:11, 7:4, 9:5, 11:6, 2:1, 9:4, 16:7, 7:3, 12:5, 5:2, 8:3, 3:1. Particularly, the 3:2, 7:4 and 2:1 are the most populated resonances in the transneptunian belt, while the 9:4 and 5:2 lead in number of members in the scattered disk. Kozai resonant TNOs are also found inside the 3:2, 5:3, 7:4 and 2:1 resonances. We present detailed features for the resonant population! s in general (i.e., libration amplitude angles, libration centers, Kozai libration amplitudes, etc.). Lastly, based on the resonant TNOs properties and dynamical lifetimes, important implications are also debated concerning the history of the solar system. Among the non-resonant TNOs, we fully characterize the so called classical TNOs and scattered TNOs defining their dynamical boundaries. Taking together the results for all TNOs, an accurate classification scheme is presented for the entire transneptunian region.
The nature of life on Earth provides a singular example of carbon-based, water-borne, photosynthesis-driven biology. Within our understanding of chemistry and the physical laws governing the universe, however, lies the possibility that alien life could be based on chemistries, solvents, and energy sources that differ from the one example provided by Earth biology. Silanes may be used as functional analogs to carbon molecules in environments very different from Earth; solvents other than water may be compatible with life-supporting processes, especially in cold environments; and a variety of energy sources may be utilized, some of which have no Earth analog. Examples of possibilities for unconventional life in the Venusian clouds and on Titan?s surface will be discussed.
Most origins of life theories postulate that molecular organic sources were present on the early earth, from which biochemical monomers could have appeared. Then the synthesis of macromolecules is described leading to the RNA world before the appearance of protocells, then to the DNA/proteins world. If we can be confident concerning the origins of the building blocks of life other steps remained to be experimented in laboratory conditions. I will present the hypotheses and questions on the early steps of the history of life. Is there any relationship between prebiotic chemistry and biochemistry? Role of natural selection in water or mineral surfaces debate ? Pros and cons the RNA world hypothesis which proposes that informational molecules came first. Could RNA have been capable of resisting under primitive conditions, such as extreme temperatures or pH, or high pressure?
We propose new results in interpreting the Cassini/CIRS spectra of the icy moons of Saturn, Phoebe, Iapetus, Enceladus and Tethys. The spectra cover the spectral range from 7mm up to 1mm, and they are almost featureless, though many end-members, such as water ice, carbon dioxide and silicates, present peculiar features in the Thermal Infra-Red. We used simulations based on the Hapke's reflectance theory, to reproduce the spectral behaviours of such moons' surfaces, as they are shown by the Cassini instrument. We find out three possible way to explain the absence of features on the spectra, playing with grain size dimensions, mixtures with dark contaminants and porosity of the surface. Constrains imposed by the Cassini/VIMS results are taken in account, showing that porosity plays a great role in affecting thermal emission of icy moons of Saturn.
The Huygens Probe detected dendritic drainage-like features, methane clouds and a high surface relative humidity on Titan in the vicinity of the landing site. These observations strongly suggest that a methane hydrological cycle is present on Titan. Cassini Orbiter remote sensing shows, globally, dry and even desert-like landscapes with dunes, although fluvial erosion appears to have been extensive. We address two questions: (i) Are the observations of atmospheric methane relative humidity and convective frequency consistent with a desert planet containing only tiny fractional lake coverage? (ii) If any lakes are observed, are hydrocarbon (methaneethane) lakes stable on the surface of Titan? We show that the high relative humidity of Titan can result from evaporation of lakes covering only 0.002 0.04 of the whole surface.
We present results of numerical simulations of convection in the outer ice shells of Enceladus and Titan, with Newtonian rheology, temperature-dependent viscosity, and tidal internal heating. We solved the Boussinesq fluid equations with the ConMan finite-element code. Convection can occur, under a range of conditions, in the ice shells of Enceladus and Titan. We discuss the thermal state of the ice shells, depending on the heat production in the rocky interior (radiogenic and tidal) and in the ice (tidal), the initial ammonia concentration, and the ice viscosity. The presence of ammonia yields small value of Rayleigh number Ra, and a Gaussian shape of the Ra vs thickness of the ice shell [Sotin et al., 1995]. We show that, consequently, two conductive-convective transitions (CCT) may occur in an ice shell. We discuss the implications of the CCTs for the geological activity.
By `late stages' we mean in this talk those phases of the solar system evolution that occurred after the dissipation of the proto-planetary nebula. Essentially, they concern three main episodes: the end of the growth of the terrestrial planets, the migration of the giant planets due to their interaction with a remnant planetesimal disk, and the late heavy bombardment.
TERRESTRIAL PLANETS FORMATION: We will present state of the art simulations of the formation of terrestrial planets (O'brien et al., Icarus, in press, 2006). These simulations account for a system of about 25 mars size planetary embryos in the terrestrial planets region and in the asteroid belt, embedded in a disk of planetesimals with equal cumulative mass. This disk is modeled with 1,000 particles of individual mass 40 times smaller than that of the embryos, which allows us to obtain the best ever achieved representation of the process of dynamical friction. We will discuss the evolution of the asteroid belt in connection with the terrestrial planets formation. We will focus on the role of Jupiter's eccentricity on the terrestrial planets' final orbits and formation timescales, as well as on the delivery of water from the asteroid belt.
GIANT PLANET MIGRATION: It was realized in the 1980's that planets will migrate if they are embedded in a disk of small objects (Fernandez and Ip, Pl. Sp. Sci., 44, 431, 1984). Such a situation existed at the end of giant planet formation at which time Uranus and Neptune migrated through a population of leftover planetesimals. The current location of the giant planets (Fernandez and Ip, Pl. Sp. Sci., 44, 431, 1984; Hahn and Malhotra, AJ 117, 3041, 1999) and the resonant structure of the Kuiper belt are probably the result of this migration (Malhotra, Nature, 365, 819, 1993; Astron. J., 110, 420, 1995; Gomes, Icarus, 161, 404, 2003). Indeed, GML04 argue that the current position of Neptune was achieved as a consequence of the Solar System's planetesimal disk being truncated at about 30 AU. If this is true, then the observed Kuiper belt was was pushed out from within 30AU (LM03; Morbidelli, Science, 306, 1302, 2004).
THE LATE HEAVY BOMBARDMENT: Planet migration can easily trigger late instabilities in the multi-planetary systems. These instabilities violently excite the disk, leading to a burst of the collisional activity among planetesimals, and may leave the planets on eccentric orbits (Tsiganis, Gomes, Morbidelli, Levison, Nature, 435, 459, 2005). In our Solar System, this process could explain the moderate eccentricities of Jupiter and Saturn. In addition, the cataclysmic Late Heavy Bombardment of the terrestrial planets, which occurred approximately 700 My after planetary formation (see Hartmann et al., in `Origin of the Earth and Moon', Univ. Ariz. press., 2000), could be elated to such an instability (Gomes, Tsiganis, Morbidelli and Levison, Nature, 435, 466, 2005). We also speculate that the IR excesses measured for hundred million years old stars (Spitzer Science Center press release ssc2004-17, and plot ssc2004-17b) are caused by similar cataclysmic events, which abruptly enhance the dust production rate.
Io-induced Jupiter emission lies mainly in the frequency range from about 2 to 40 MHz, which happens to coincide with the frequency band of the Initial Test Station of LOFAR (LOFAR/ITS).
ITS is capable of measuring the radio signal with high time and frequency resolution, which makes it well-suited for the study of Jovian decametric emission (DAM). We present the first simultaneous Io-DAM observations of Jupiter at about 700 km distance between the two instruments, LOFAR/ITS (Exloo, The Netherlands) and the Nancay Decametric Array (NDA) (Nancay, France). We have detected emission from Jupiter during snapshots of a few seconds and identified detailed features down to milli-second time scales in dynamic spectra taken with both instruments. This article presents spectra and waveform cross-correlation to demonstrate the feasibility of Very Long Baseline Interferometry (VLBI) in the low frequency band of LOFAR. By adding remote stations to the LOFAR network at this baselines will provide the instrument with an arcsecond spatial resolution.
The global transforms model (bursa -wolf , molodensky-badekas) are the famous method used to cmpute parameter tansformation between geodetic systems. In our case , for a huge territory like algeria , these model are not most appropriate to give a good accuracies over these parameters, because informatuion about local geoid over ellipsoide clarke 1880 is not available but the two dimension models such as geodetic lines , multiple refression ,..., have given bes results applied over the algerian area. That's why we are hold to use a new method to compute the tansform parameters with good accuracies, this method is called "zonage" and it concist to delimitate our territory to little zone in order to apply three dimension models (bursa- wolf, molodensky-badekas) , in this case we can avoid great geoid undulation wich generate errors on computation of patrameters and give thus a bad accuracy. These parameters while computed, we can use them to transform a new point over all the zone, the results are validating by a computation programm called TRANSFOR.
There exist many reasons to believe that the synthesis of organic substances does place in Interstellar Space. Accordingly, a cosmic dust particle can be considered a logical place for the synthesis of organic species.The energy of excitation which has formed by influence of UV radiation on a mineral surface and accumulated there owing to "photocatalytic memory effect" can be realyzed for activiation of chemical reactions at this surface at proper conditions.In this work it is shown experimentally, that at adsorption of molecules adenosin 5'-monophosphate on preliminary undergone UV to an irradiation a mineral surface oligonucleotides are formed.
Europa may be a habitable world. Evidence points strongly to a subsurface ocean beneath an ice shell about 20 km thick. Tidal flexing and nonsynchronous rotation of the floating ice shell generate stresses that can fracture the surface to create Europa's ubiquitous troughs and ridges. Mottled terrain (pits, domes, dark spots, smooth plains, and chaos) may be linked to ice convection. Tectonics and convection can create localized melt, and surface-ocean exchange is plausible. A nominal surface age of 60 million years implies that Europa is probably still active today. Its astonishing geology and astrobiological potential makes Europa a high priority for spacecraft exploration.
We show that the current polar location of the south polar hot-spot of Enceladus can be explained by reorientation of the satellite's
rotation axis due to the presence of a large low-density diapir. If silicate diapirism is responsible for the reorientation, Enceladus cannot possess a global subsurface ocean, while ice diapirism requires a relatively rigid ice shell (elastic thickness \grsim0.5 km). The reorientation we propose generates large ( ~ 10 MPa) tectonic stress patterns that are compatible with the observed deformation of the south polar region. A low-density diapir yields a potentially
observable negative gravity anomaly and would affect the satellite's observable cratering record.
This work investigates the stability properties of the complete set of isothermal protoplanetary equilibrium solutions (Pecnik Wuchterl, A A, 2005).
To perform a non-linear stability analysis, we introduce a fluid-dynamics numerical model. We inspect entire solution set and find five basic dynamical modes: oscillation, pulsation, transition, ejection, and collapse.
We find that a subcritical cores can experience a whole diversity of dynamical phenomena. This could influence on how the protoplanetary evolution up to critical core-mass is presently seen.
Nine transiting exoplanets are now known. After the discovery of the first of them, HD 209458b, photometric transit surveys of bright stars were expected to open the way of the detection of many more. In the event, however, spectroscopy proved just as crucial as photometry in the effort to determine empirically the radius and structure of exoplanets. Of the nine transiting planets, only one was discovered by surveys of relatively bright stars. Three were first found by radial velocity searches, and five were found by among faint stars requiring a spectroscopic effort of similar magnitude to the photometry. Our group was involved on seven of these nine objects, pushing the limits of radial velocity measurements in terms of accuracy and limiting magnitude.
Observed from Earth orbit in FUV and X wavelength with high spatial resolution since 1994, Jovian aurorae are produced, like on Earth, by precipitation at high latitude of energetic particules along planetary magnetic field lines. If Earth aurorae are controlled by the solar wind, the two jovian main ovals are magnetically conjugated to the middle magnetosphere (20-30 jovian radii), filled with plasma from the satellite Io. At higher latitude than the main oval, the FUV emission associated to the polar cusp (region of the dayside magnetosphere between open and closed field lines) is highly variable. Solar wind conditions have been observed by the Cassini spacecraft before flyby of Jupiter in december 2000. A series of interplanetary shocks have been recorded during this period, coinciding with a strong emission of the FUV cusp observed with the Hubble Space Telescope.
After more than 10 years of successful researches, the realm of extra-solar planet keep providing its lot of surprises and informations to understand the formation and the structure of planets in an universal context. In addition, it captures the interest of both scientists and the public with the haunting prospect of the search for life in the Universe. In my talk I shall review recent results obtained both from radial velocity surveys as well as measurements of transiting planets. These two different sets of data provides a mean to gather information on planetary formation processes, to capture the planet diversity as well as to get some insight on the structure and physics of hot Jupiter planets.
Methane cycle on Titan is still largely unknown. On the timescale of several years, dynamics, cloud and rain cycles can redristribute, on a global scale, methane at the surface. On timescale of million years, methane is destroyed by photodissociation and disappears. In this work, we consider the fate of methane due the short timescale cycles only.The detection of many types of clouds, and the measurement of the methane vertical profile by GCMS have given strong constraints on Titan climate and on the cloud and methane cycle. With a 2 D circulation model, including cloud microphysics, we study various scenario of methane source. We determine the regions of the planet where methane is stable on Titan, and regions where rains occur. We also consider what happens when sudden release of methane occurs, and how it is finally distributed at the surface of the planet.
SPICAM, a light-weight (4.8 kg) UV-IR dual spectrometer on board Mars Express orbiter,is dedicated primarily to the study of the atmosphere and ionosphere of Mars, but is providing important results on the surface albedo of Mars. A UV imaging spectrometer (118 - 320 nm, resolution 1.5 nm, intensified CCD) operates in nadir viewing, limb viewing and atmospheric vertical profiling by stellar and solar occultation. An IR spectrometer (1.0-1.7 microns, resolution 0.5-1.2 nm, or = 1300, mass 0.8 kg) is dedicated primarily to nadir measurements of H2O abundances, but detects also water ice and CO2 ice both on perennial and seasonal caps. It is based on AOTF technology; and it is the first time that such a spectrometer is flying in deep space. Night glow emissions from NO recombination and aurora over crustal magnetic
anomalies have been discovered. Several hundreds of atmospheric vertical profiles by UV star occultation were obtained. The main absorbers are CO2 (below 200 nm) and aerosols/dust (above 200 nm). The atmospheric pressure and temperature are retrieved from 150 km down to 25-40 km, for the construction of an empirical model of the atmosphere. In 60 detached layer of dust, or cloud. Ozone is also measured and compared to model predictions. The UV absorption of ozone is well identified in routine reflectance nadir viewing. The ozone vertical quantity is recovered along the orbital track, and compared to the water vapour distribution measured by SPICAM in the near Infra-red around 1.38 µm. SPICAM has thus obtained for the first time from an orbiter simultaneous measurements of ozone and H2O, which are found to be somewhat anti-correlated as expected on the ground of chemistry consideration: catalytic destruction of ozone from OH and HO2 radicals. We observed also the O2 Airglow at 1.27 µm in nadir and limb viewing produced by photo-dissociated ozone, and all UV limb dayglow emissions that were observed by Mariner spacecraft.
Largest satellite of Saturn and the only satellite in the solar system having a dense atmosphere, Titan is one of the key planetary bodies for astrobiological studies, due to several aspects:
Its analogies with planet Earth, in spite of much lower temperatures. The Cassini-Huygens data have largely confirmed the many analogies between Titan and our own planet. Both have similar vertical temperature profiles, (although much colder, of course, on Titan). Both have condensable and non condensable greenhouse gases in their atmosphere. Both are geologically very active. Furthermore, the data also suggest strongly the presence of a methane cycle on Titan analogous to the water cycle on Earth.
The presence of an active organic chemistry, involving several of the key compounds of prebiotic chemistry. The recent data obtained from the Huygens instruments show that the organic matter in Titan low atmosphere (stratosphere and troposphere) is mainly concentrated in the aerosol particles. Because of the vertical temperature profile in this part of the atmosphere, most of the volatile organics are probably mainly condensed on the aerosol particles. The nucleus of these particles seems to be made of complex macromolecular organic matter, well mimicked in the laboratory by the "Titan's tholins". Now, laboratory tholins are known to release many organic compounds of biological interest, such as amino acids and purine and pyrimidine bases, when they are in contact with liquid water. Such hydrolysis may have occurred on the surface of Titan, in the bodies of liquid water which episodically may form on Titan's surface from meteoritic and cometary impacts. The formation of biologically interesting compounds may also occur in the deep water ocean, from the hydrolysis of complex organic material included in the chrondritic matter accreted during the formation of Titan.
The possible emergence and persistence of Life on Titan All ingredients which seems necessary for Life are present on Titan :
Thus, it cannot be excluded that life may have emerged on or in Titan. In spite of the extreme conditions in this environment life may have been able to adapt and to persist.
Many data are still expected from the Cassini-Huygens mission and future atsrobiological exploration mission of Titan are now under consideration. Nevertheless, Titan already looks like another word, with an active prebiotic-like chemistry, but in the absence of permanent liquid water, on the surface: a natural laboratory for prebiotic-like chemistry.
ISSI Workshop on "Habitability and Terrestrial Planets" Bern, Swizterla
Models of terrestrial planet formation can constrain the systems likely to harbor habitable planets. We examine the effects of two observables: stellar mass and the orbit of a giant planet. The protoplanetary disk mass scales with stellar mass as M*h, where h=0-2, so disk mass decreases with decreasing stellar mass. Assuming a lower mass limit for habitability, the fraction of systems that can form habitable planets decreases for low-mass stars. A suite of simulations shows that Jupiter-mass giant planets inside 2.5 AU disrupt the formation of planets in the HZ; water-rich planets in the HZ can only form if the giant planet's orbit is beyond 3.5 AU. Less than 10% of the known planetary systems can form habitable planets.
The Rosetta Orbiter Spectrometer for Ion and Neutral Analysis is designed to analyze the volatile material of comet 67P/Churyumov-Gerasimenko. The ion measurements in the vicinity of a comet are of great interest: They give insight into the important processes of the interaction of the solar wind with the comet as well as into the chemistry in a cometary coma. For the ROSINA ion mode calibration in the lab an external source is needed, providing the two mass spectrometers DFMS and RTOF with an ion beam according to the expected plasma environment at the comet. Especially the low energy of the cometary ions, typically below 20eV, makes a new ion source setup necessary. We discuss this design and the results of the source characterization.
Studying the divergent evolution of Venus, the Earth and Mars in our solar system has lead to the concept of circumstellar habitable zone: the region around a star where Earth-like planets receive an amount of stellar energy compatible with the maintenance of surface liquid water over geological timescales. Being inside this radiative habitable zone is not the only requirement for habitability. Indeed, other factors may prevent a planet from developing a biosphere:
- the composition of the planet, in particular its content in water and volatiles,
- the mass of the planet, which determines its cooling time, its ability to recycle and retain an atmosphere against gravitational escape,
- the stellar activity, which produces enhanced X-EUV irradiation, stellar wind, and coronal ejections that can induce severe atmospheric losses,
- the presence of giant planets, which gravitational influence can affect the orbital stability inside the habitable zone.
We will show some recent results illustrating some of these effects. We will also discuss how future space observatories such as Kepler, Darwin and TPF could allow us to identify habitable planets, focusing on the main observational challenges we need to overcome in order to test our theoretical understanding of terrestrial planet evolution and habitability.
Stellar occultations are powerful tools to probe planetary rings and atmospheres, and to precisely measures sizes - to within kilometric accuracy- for bodies at more than a billion km away. We present occultation soundings of Titan's and Pluto's atmospheres. Various expeditions to observe such events revealed gravity waves in Titan's atmosphere, the aerosol distribution, and the zonal wind regime at 0.25 mbar pressure level. Pluto occultations have shown that atmospheric pressure doubled from 1988 to 2002, a paradoxical result, considering than the planet is receding from the Sun, thus cooling. This counter-intuitive finding is the result of violent seasonal effects, where Pluto's southern polar cap is being sublimated after more than 120 years in darkness.
The upper atmospheres of Jupiter and Saturn are driven to a large extent by plasma flows in the magnetosphere. These flows induce inputs of energy and momentum which strongly influence the thermal and dynamical structure of the thermosphere. The magnetospheric flows are in turn driven by the motion of the thermosphere.
We employ a three-dimensional general circulation model to study this interaction. The role of meridional (north-south) winds is found to be of critical importance in the flow of energy and momentum within the thermosphere. This has implications both for the thermal structure of the upper atmosphere and for the nature of the flows in the magnetosphere itself.
The magnetospheres of Jupiter and Saturn exhibit significant rotation because angular momentum is transferred from the planet via ion-neutral collisions in the upper atmosphere. The standard viewpoint of this process holds that the angular momentum so extracted from the upper atmosphere is replaced by upwards viscous transfer of angular momentum from the lower atmosphere. The efficiency of this process is normally described by a parameter known as the `effective' conductivity.
However, thermospheric modelling shows that the conventional model is inadequate. This poster explores the circumstances under which the effective conductivity remains a useful parameter, and considers the possibility of alternative parameterisations.
The underpinning of planetary interior structure models is based on theoretical calculations simultaneously satisfying the available observational constraints provided by remote sensing, in-situ measurements, and laboratory data. The terrestrial planets Mercury, Venus, Earth, and Mars have low masses, small radii, and large densities in comparison to the giant planets in the outer solar system. This is also valid for terrestrial-type bodies like the Moon and some of the outer planets satellites and provides important clues on their bulk compositions. Gravitational and magnetic field observations indicate that the interiors are strongly differentiated and subdivided like that of the Earth into iron-rich cores, silicate mantles, and rocky crusts derived from partial mantle melts. The cores and the primary crusts formed early and rapidly as isotope data indicate. Geodetic observations of the rotational state and/or tidal response suggest that the interiors are warm enough to maintain liquid outer core shells or entirely liquid cores. For Mars, Venus, and Earth, mantle pressures are sufficient to permit mineral phase transformations from olivine and pyroxene assemblages to spinel or even perovskite and post-perovskite phases. Since the phase transition depths do also depend on the ambient temperature and the iron content of the mantle rocks, future seismological observations at planetary surfaces would have the potential to provide additional information on the thermal states and compositional differences of the terrestrial planets. Single-plate planets, as the Moon, Mercury, Mars, and Venus, are believed to be cooling by lithospheric thickening while the deep interior remains relatively hot. It is likely, therefore, that in the course of progressive cooling of the planet's outer portion, thermo-elastic stresses will be occasionally released at pre-existing faults thereby causing local seismic activity at a level detectable by seismometers. The possible freeze-out of an inner iron core upon cooling is dependent on the composition of the core alloy and the time rate of change of the core temperature. The power required to sustain a dynamo-driven planetary magnetic field, as on the Earth and Mercury, should be provided by the chemical bouyancy upon solidification of an inner core. Furthermore, plate recycling is highly efficient in cooling the core from above and, therefore, helps sustain the Earth's dynamo. The present lack (and possible early presence) of plate tectonics and magnetic fields on Mars and Venus suggests that inner-core growth does not play a role today and the cores may have become stably stratified soon after planet formation.
The detection of induced magnetic fields in the vicinity of the icy Galilean satellites suggests the existence of electrically conducting reservoirs of liquid water beneath their outermost ice shells. This is consistent with recent models of the satellite interiors thought to be differentiated into rock cores and water-ice liquid shells and assuming thermodynamic equilibrium between the radiogenic heat production in the silicates, additional contributions due to, e.g., the dissipation of tidal energy in case of Europa, and the effectiveness of the heat transfer through the outer ice shell. Furthermore, the significant melting point reduction of water-ice liquids in the presence of small amounts of salts and/or incorporated volatiles such as ammonia is also conducive to the formation of sub-surface oceans. The slightly pressure-dependent minimum melting temperature of ammonia-water liquids close to 176 K is attained at the peritectic composition of about 32.5 wt.ammonia. Due to slower cooling rates and more intense radiogenic heating caused by larger rock mass fractions, large icy bodies such as, e.g. the icy Galilean satellites, Titan and Triton, are more likely to harbour sub-surface oceans as compared to smaller icy bodies. However, depending on the initial amount of ammonia incorporated in the icy component during accretion, internal oceans with compositions close to that of peritectic ammonia-water liquids may have survived up to the present day on the largest of the medium-sized satellites of Saturn (Rhea) and Uranus (Titania, Oberon) and on large Kuiper-belt objects (Pluto, Charon, Xena, Sedna, and other 1000-km-class bodies) in the outer solar system. To maintain present-day internal oceans with peritectic compositions at shallow depth even on small icy bodies like Miranda, Mimas, or Enceladus, a significant amount of internal heating other than that caused by long-lived radiogenics in the rock component would be required. For the bodies considered in this study, the liquid reservoirs are in direct contact with the rocky cores beneath, like on Europa. This contrasts with subsurface oceans on large icy satellites like Ganymede, Callisto, and Titan, where they are enclosed between outer ice shells on top and high-pressure ice layers at the bottom. The silicate-water contact would allow a highly efficient exchange of minerals and salts between the rock core and the overlain ocean in the interiors of these medium-sized satellites and large Kuiper belt objects. The sub-surface oceans mav be situated deeply beneath several 100 kilometres thick ice-I shells and, therefore, not necessarily visible in the geological surface record. However, internal oceans may be indirectly detectable from spacecraft by their interaction with surrounding magnetic fields and charged particles and by the magnitude of the tidal response of the outer ice shell mechanically decoupled from the deep interior.
The Galileo mission revealed that the Galilean icy satellites are differentiated. The magnetic data suggest that Ganymede has a liquid iron-rich core and that a conductive layer, likely to be a salty deep ocean, is present below the ice crust of Europa and Callisto. Progress in modelling the heat transfer suggest that tidal heating plays an important in the dynamics of Europa. The Cassini spacecraft has revealed that Titan's surface is not covered by a global hydrocarbon ocean that could explain the amount of methane in its thick atmosphere. An alternative model involving a deep reservoir and cryovolcanism has been proposed. Cassini observations also revealed the cryovolcanic activity of Enceladus, a very small icy satellite. Icy satellites are very active bodies where processes similar to those existing on Earth, operate.
Since its successful orbit insertion around Saturn in July 2004, the Cassini spacecraft has realized 10 flybys of Saturn's largest moon Titan. The Visual and Infrared Mapping Spectrometer (VIMS) can map Titan's surface within 7 windows between 930 nm to 5000 nm. The spectral characteristics within each window and the global shape of the spectrum provide information on surface composition. Two-third of Titan's surface has been observed at a resolution lower than 50 km/pixel but only 0.3 observed at a resolution lower than 5 km. These data suggest that Titan's surface is young with potential cryo-volcanic features. It is covered with a material not yet identified.
The data obtained by the Cassini spacecraft revealed that the mid-sized satellites of Saturn have been shaped by internal processes. By comparison with Earth, it is tempting to invoke thermal convection as a driver for tectonics and resurfacing. We have investigated the conditions required for the onset of convection in these satellites. This study suggests that rapid accretion, trapping short live radiogenic elements in the satellite, favours convective processes. However, convection can only exist for short period of times. Implications for Iapetus and Enceladus are described.
We investigate increased N2O flux into the atmosphere of an earthlike planet. The planet is in the Habitable Zone around a main sequence star with an earthlike biosphere. N2O is an ideal biomarker produced almost exclusively from biogenic sources and is emitted via denitrifying bacteria. To investigate the effect of increased N2O we have used a coupled radiative-convective photochemical column model. Stratospheric N2O photolysis is a significant source of NOx which destroys O3. Therefore, we propose biomarker "regimes" i.e. a) a low N2O regime, where O3 is easier to measure, but N2O may be impossible, b) a high N2O regime, where the opposite is true and c) a medium N2O regime, where both may be measureable.
The California and Carnegie Planet Search has obtained high-quality echelle spectra of over 1200 nearby stars at Lick, Keck and the Anglo-Australian Observatory. Combining various observations with spectral synthesis modeling, Valenti and Fischer (2005) provided precise determinations of Teff, vsin(i), log(g), and several metal abundances. We have created an extensive and fine grids of stellar evolutionary tracks. Combining the grids with the spectroscopic observations and Hipparcos data and adopting careful analysis methods such as the Bayesian probability theory, we have produced reliable models of over 1000 stars to explore the physical properties of the stars harboring planets.
A scientific account will be given of the Venus Express mission and its objectives. Particular attention will be paid to the open questions the mission was designed to address, and how these relate to an overall understanding of the planet and its place in the Solar System. The relationship between various phenomena on Venus, such as the extreme greenhouse effect and the circulation of the atmosphere, and analogous phenomena on the Earth will be developed. Finally, it is hoped that some early data can be presented following the successful arrival of the spacecraft at Venus and its insertion into orbit, expected on 11 April 2006.
We will describe results of a concerted research effort held in "Laboratoire de Chimie Physique", where experimentalists as well as theoreticians, have developed laboratory tools in order to measure accurate rates of ion molecule reactions, and tools to estimate the uncertainty propagation in the models of Titan Ionosphere, which are becoming increasingly complex. some laboratory measurements were performed, but triggered the development of a new experimental set-up, that will be installed in the next months in "Laboratoire de Planétologie de Grenoble". A very high resolution mass spectrometer is proposed to study the Titan ionosphere Chemistry. A parallel modelling effort with uncertainty analysis will be conducted in Orsay and Grenoble.
Tidal forces probably play a major role in the generation of the South Polar Hot Spot recently discovered by Cassini on Enceladus (Spencer et al. Science, 2006). However, the large observed heat flux and its particular location at the South Pole remains quite puzzling. Here we perform numerical calculations of tidal dissipation using viscoelastic axisymmetric 2D models and assuming heterogeneous distributions of viscosity within the interior. We investigate how tidal dissipation can be focused at the South Pole and how a high temperature anomaly can self-sustain there.
Saturn's satellite Iapetus shows one of the most striking dichotomies in the Solar System, with the leading side significantly darker than the trailing side. Understanding the origin of the dark material coating the leading hemisphere of Iapetus is a focus of the Cassini mission. Proposed sources of the accreted particles are Phoebe and Hyperion, or even other small dark bodies. In this work, we applied the G-mode clustering method on the infrared and visible spectra collected by Cassini/VIMS in order to find indications about possible spectral correlations among the three bodies on the basis of many weighted variables.
The irregular moons of the giant planets are intriguing minor bodies of the outer Solar System which dynamical features argue against an in-situ formation and suggest they are captured bodies. Our study of the irregular satellites of Saturn aims to understand which ones of such dynamical features are primordial and which ones are a product of the secular evolution of their orbit. Our results suggests that Saturn's irregular satellites are subjected to a strong sculpting by the tidal effects of the Sun and Jupiter, indicating that the system is dinamically evolved. We found hints of the existence of collisional families and that the orbital behaviour of the satellites can bear indications on the dynamical nature of the parent bodies.
The diversity of icy satellite surfaces observed throughout the outer Solar System attests to the wide variety of processes that act to shape them, and serves to underscore the significance of the conditions under which the bodies formed and evolved. The Saturnian satellites provide valuable examples: despite having formed in the same system, their surfaces vary dramatically and attest to the divergent histories experienced by the satellites, from heavily cratered Mimas, to the contrasting styles of tectonic deformation exhibited by Iapetus, Tethys and Dione, to the active plumes on Enceladus. Comparison of these bodies provides important insights into the roles of various characteristics of icy satellites for their formation and evolution.
The first Super-Earth was discovered last June with a mass of 7.5 times the mass of the Earth. Our models predict its total radius and internal structure. If we assume an Earth-like composition the planet would have a radius of 11000km. The period of this planet is only 1.94 days and the surface temperature is calculated to be 550K. Despite the proximity to its parent star this planet might have formed beyond the snow line and accreted a substantial amount of water/ice. Provided the surface pressure is 10MPa the planet could have a stable layer of a high-pressure form of ice (ice VII). If the planet has an ice/water layer of 40
Additionally, the Earth is the only planet to exhibit plate tectonics in the Solar system, and it might not be a coincidence that it is also the most massive rocky planet. Simple analysis using parameterized convection equations yield that massive terrestrial planets have vigorously convecting mantles that exhibit fast convective velocities and a thin top boundary layer, properties that can facilitate the subduction of the lithosphere and allow for the onset of plate tectonics.
The Ion and Neutral Mass Spectrometer (INMS) performed the first composition measurements of Titan's ionosphere during the T5 close pass by the Cassini spacecraft through Titan's upper atmosphere. Although the closest approach occurred on the nightside, INMS detected approximately 50 ion species, including numerous nitrogen-bearing species. The presence of these species implies that nitrogen chemistry on Titan is more extensive than expected by the pre-Cassini models. By using the measured density of ions and a simple chemical model for ions containing up to 4 (C+N) atoms, we retrieve the mole fractions of C2H4, C4H2, HCN, HC3N, CH3CN, C2H3CN, C2H5CN, NH3 and CH2NH. The latter four species have not previously been detected in the gas phase on Titan and none of these species have been accurately measured in the upper atmosphere.
I present a new approach to planet formation theory that is centered around a classification of the equilibria of self-gravitating gas spheres.
A physical description based on the radiation fluid dynamics with convection is developed and calibrated to the Sun. The equations are then applied to all plausible `nebula' or `cloud' conditions in an effort to derive all possible resulting celestial bodies. Thus a general framework for star, brown dwarf and planet formation is set up and used to derive properties of the resulting populations.
Two applications are shown for illustration: (1)The origin and nature of the GQ Lupi system, (2)A prediction of the properties of COROT's planetary population.
Following a brief review of the history and outstanding problems related tovertical mixing and escape of Titan atmosphere, we present new resultsbased on measurements made from the Cassini/Huygens mission. Weanalyze and compare results from the Ion Neutral Mass Spectrometer (INMS),which measures density and chemical composition in the thermosphere,and the Gas Cromatograph/Mass Spectrometer (GCSM), which measuresdensity and chemical composition in the troposphere, to infer the verticalmixing rate and the escape rate of light species. The altitude variation of Argon provides the best constraint on the vertical mixing rate and suggestthat previously determined high values of the eddy diffusion coefficient,derived from the CH4 profile, may actually be the signature of a rapid escape flux. Analysis of the vertical profiles of H2, and HD establish the escapeflux for these species. The role of global variations, its effect on comparisonof INMS and GCMS measurements and the vertical profile of CH4, H2, andHD will also be discussed.
Planetary magnetospheric strucutre
Philippe Zarka, Observatoire de Meudon
File translated from TEX by TTH, version 3.73.
On 23 May 2006, 23:01.