______Bourdarie S.

Radiation belts and their interactions with solid bodies In ANALYSIS: External processes: interact. with atmosph. and space environ. (Thursday afternoon)

______Burger M University of Maryland-Baltimore County and NASA/GSFC

Interactions between satellites and magnetospheres in the outer solar system In ANALYSIS: External processes: interact. with atmosph. and space environ. (Thursday afternoon)

The satellites of Jupiter and Saturn interact with the planetary magnetospheres to produce tenuous atmospheres or exospheres. These atmospheres are stripped away by sputtering and ionization by magnetospheric plasma to produce neutral gas clouds and supply fresh plasma. I will briefly review three cases in the outer solar system of the interactions between satellite atmospheres and the magnetospheres in which they are embedded. Gases in Io's atmosphere are supplied by the volcanoes and achieve a rough balance with frost on the surface. Interactions between the atmosphere and surface with plasma and high energy particles in Jupiter's magnetosphere produce fresh ions which are swept up by the magnetic field and form the Io plasma torus, a ring of plasma encircling Jupiter which extends from inside Io's orbit out beyond Europa. Neutrals also escape from Io through both slow and fast escape processes. Sputtering of the atmosphere results in slowly (~2 km/s) escaping neutrals which form a partial torus neutral cloud orbiting Jupiter. Resonant charge exchange between Na+ ions in the plasma torus and Na in the atmosphere produce fast neutrals which form a sodium jet whose orientation varies with Jupiter's magnetic field.

W hen high energy ions impact Europa's surface, H2O, O2, and H2 are ejected. The hydrogen escapes from Europa, and most of the water molecules return to the surface and stick. The O2, however, neither immediately escapes nor returns to the surface, but instead builds up forming a tenuous atmosphere. This atmosphere is ultimately limited by its interaction with the Io plasma torus: charge exchange with the ions and dissociation and ionization by the electrons remove material and produce emissions which have been observed by the Hubble Space Telescope and Cassini.

W hile Enceladus does not have a full exosphere, the interactions between its south polar plume and Saturn's magnetosphere are similar to the atmosphere/plasma interactions at

Jupiter. H2O escaping from Enceladus forms a neutral torus around Saturn. Charge exchange and neutral-neutral reactions in this torus redistribute neutrals throughout the magnetosphere, providing an extended source of plasma.

______Cassidy T.

Space weathering and magnetospheric interactions In ANALYSIS: External processes: interact. with atmosph. and space environ. (Wednesday morning)

Most of the icy satellites in our solar system are embedded in their parent planet's magnetosphere, where they are exposed to energetic ion and electron bombardment that erodes and alters their surfaces. Ion erosion (sputtering) launches molecules on ballistic arcs above the surface, forming tenuous "atmospheres" representative of surface composition and space weathering processes. The incoming plasma also alters surface composition by breaking molecular bonds and introducing new material to the surface. I will discuss these processes and their importance on the icy satellites of Jupiter and Saturn and Saturn's E ring.

______Coll P.

Tholins œ a way to understand the organic complexity of Titan In DATA/FACTS : Physics and chemistry of ices and organics (Tuesday afternoon)

______Coradini A. A. Coradini, G. Magni, D. Turrini

Initial conditions in circumplanetary nebulae in IMPLICATIONS : Origin of the moons (Friday morning)

Early stages of planetary satellites formation are possibly related to the condition characterizing Jupiter and Saturn subnebulae. The nature and life-time of these nebulae depend, in turn, on the formation scenario assumed for giant planets' formation. If giant planets form through rapid gas-accretion onto a previously formed solid core, then the formation of planetary subnebulae, which then evolve into circumplanetary disks, is a by- product of the planetary formation process. During the first rapid accretion phases, disks are relatively hot, turbulent and partially embedded in their planets‘ atmospheres. At later stages, when the accretion slows down, the disk's turbulence decreases accordingly and different ices can condense. Understanding the thermodynamical evolution of the disks surrounding the giant planets is mandatory to understand the origin of the satellites. W e will describe the disk's thermodynamical state at the end of the accretion phase and we will compare its chemistry with present data on the composition of the satellites.

______Coustenis A. - Lunine J.

LESIA Observatoire de Meudon

Analysis of Titan surface and atmosphere infrared data" In ANALYSIS : External processes: interact. with atmosph. and space environ. (Wednesday morning)

Titan observations in the far- and near-infrared have led to a better comprehension of the complex chemical and surface composition of the satellite. I will discuss methods for analyzing Cassini-Huygens and ground-based data and the impact this investigations have had on our understanding of the satellite's processes.

______Dalton B. Jet Propulsion Laboratory

Spectroscopy of Planetary Ices in Support of Spacecraft Missions In DATA/FACTS : Physics and chemistry of ices and organics (Tuesday morning)

The advent of modern imaging spectrometers has created exciting opportunities to discern the composition and distribution of surface materials on solid bodies of the Solar System. In the outer Solar System, recent and planned missions have begun to return a vast library of observations specifically concerned with the icy satellites. Interpreting this data and understanding the operative processes that have led these worlds to their present states, requires a concerted and collaborative effort which combines laboratory spectroscopy at relevant temperatures, wavelengths, viewing geometries and sample characteristics, with advanced automated spectral and image processing techniques which take into account the characteristics, capabilities and limitations of modern instrumentation.

______Durham W . Massachusetts Institute of Technology, Cambridge, MA, USA

Rheology of icy materials under planetary conditions In DATA/FACTS : Physics and chemistry of ices and organics (Tuesday morning)

This review of the rheological properties of planetary ices as seen from the viewpoint of laboratory experiments will cover six topics: (1) a review of the basic language of rheology– the study of the rate at which materials undergo a permanent change of shape under deviatoric stress –and the practical methods by which one goes about determining flow properties under planetary conditions of high pressure, low temperature, and low strain rate; (2) a comparison of the relative strengths of single-phase ices, from the very strong sulfate hydrate salts and clathrates, to water ice phases I through VI, to weaker ices of ammonia and carbon dioxide; (3) a discussion of grain-size-sensitive vs. grain-size-insensitive mechanisms of flow in crystalline materials and current ideas about dynamic changes in grain size, with an emphasis on ice I in the laboratory and in the outer layers of icy moons; (4) an introduction to the complexity of the rheological behavior of two- and multi-phase materials, with examples

of several ice-ice systems; (5) a presentation of new results in one specific two-phase system, that of water ice plus silicate dust; and (6) a discussion of future directions for the field, including the rheological behavior of ice + liquid mixtures with and eye toward the crust of Titan. The objective here is to communicate a practical knowledge of the strength differences between various ices, and a basic understanding of the more important factors that influence those strengths in the planetary setting.

______Fortes D. STFC Advanced Research Fellow Department of Earth Sciences University College London

Instability of hydrates in planetary interiors In DATA/FACTS : Physics and chemistry of ices and organics (Tuesday morning)

Experimental studies in recent years have revealed that, in general, most ofthe hydrated phases expected in icy satellite interiors are unstable with respect to lower hydrates as pressure is increased. My work at UCL on ammonia dihydrate and MgSO4 7- and 11-hydrates is reported, and agrees with the trend observed also in Na2SO4 hydrates and in clathrate hydrates towards stabilisation of lower hydrates with pressure. It is predicted that sulfuric acid hydrates will behave in the same way, the octahydrate giving way to lower hydrates at kilobar pressures, for example. The volume changes (and change in transport properties) associated with these dehydration reactions may have significant consequences for the internal structure and evolution of icy satellites. The presence of 'unexpected'phases on the high-pressure liquidus may also have consequences for the subsurface ocean chemistry in these bodies.

______Giese B. DLR, Institute of Planetary Research, Rutherfordstr. 2, 12489 Berlin, Germany

Lithosphere dynamics: flexure and relaxation in ANALYSIS : Past and present dynamics of icy surfaces (Wednesday morning)

A lithosphere is not a fundamental quality of a planetary body; it instead is the expression of the response of the near-surface of a planet to a particular mechanical and thermal state. Lithospheric thickness thus holds important information on the stresses and thermal state of the body at a certain time and location. A surface expression of the body‘s response to stresses is topography. W hile impact craters are also probes of the lithosphere, topography has widely been used to infer lithosperic thickness and associated heat flux. In this talk I‘m going to present different methods of how this was done, and I‘ll show examples of topography from several icy satellites where these methods were applied.

______Hand K.

Habitability of Europa and Enceladus In IMPLICATIONS : Exobiology, habitability and planetary protection (Tuesday afternoon)

Icy worlds with subsurface oceans or seas present compelling places to search for life beyond Earth because they may satisfy one of the prime requirements for life as we know it: the need for liquid water. Beyond this requirement, life on Earth is constrained by the need for elements essential to life (e.g. C,H,N,O,P,S, and many trace metals) and the need for energy that can be extracted from the environment in order to do work (i.e. a negative change in Gibbs free energy). Here I present a comparison between Europa and Enceladus in the context of these latter two constraints. Empirical results and numerical models for the possibility of water-rock interactions, both past and present, on both worlds will be discussed. Chemosynthetic pathways for metabolism and various fluxes for required compounds will be presented in the context of energetic requirements for life. An emphasis will be placed on the possible role of radiolytic surface processing as a means for oxidizing subsurface oceans.

Finally, I will address several of the challenges facing the planetary science and astrobiology communities as we search for signs of life on Europa and Enceladus.

______Hussmann H. DLR, Institute of Planetary Research, Rutherfordstr. 2, 12489 Berlin, Germany

Internal Energy sources of Outer Planet Satellites In ANALYSIS: Internal processes: energy sources and dynamics (Thursday morning)

Energy driving the thermal evolution of solid planetary bodies is generally provided by the decay of long-lived radio-isotopes within their silicate layers. However, thermal energy due to tidal flexing can be an important œ and in some cases the dominating œ heat source in outer planet satellites. In contrast to the exponentially decreasing radiogenic heating rate, tidal heating will depend on a satellite's dynamical (rotational and orbital) state and on its thermal (rheological) state which both can be coupled and may thus vary significantly with time. Potential energy released by differentiation or latent heat released due to phase transitions are examples in which the amount of thermal energy available in the satellite's interior will depend on physical processes ongoing within the satellite itself. Different episodes and regimes of internal heating and corresponding degrees of geologic and thermal activity are consequences of these couplings. Focusing on moons that were geologically active in their recent past or early in their evolution, the significance of different kinds of energy sources in the satellites' histories will be compared for individual moons. Implications for their present states will be discussed.

______Iess L. Univ. La Sapienza

The gravity fields of the solar system satellites In DATA/FACTS : Physical constraints (Tuesday morning)

The current knowledge of the gravity fields of the outer solar system moons comes from a handful of flybys of the Galileo and Cassini spacecraft. Doppler tracking from ground using

microwave links provides the main observable quantity from which the mass and the low degree harmonics coefficients can be estimated. Being derived from flybys, the determination is unavoidably affected by undersampling, Disentangling the global field and local gravity anomalies requires good data quality and multiple flybys. The talk will review our current knowledge of the gravity field of the Jovian and Saturnian moons, together with the assumptions used in their estimation.

______Jaumann R. 1DLR, Institute of Planetary Research. Rutherfordstrasse 2, 12489 Berlin, Germany; 2Dept. of Earth Sciences, Inst. of Geosciences, Freie Universität Berlin, Germany; (ralf.jaumann@ dlr.de)

Geological features on Titan In DATA/FACTS : Surface and atmosph. characteristics œspecific bodies (Monday afternoon)

Introduction: The surface of Titan has been revealed globally, if incompletely, by the Cassini observations in the infrared and radar wavelength ranges as well as locally by the Huygens instruments. Extended dune fields, lakes, distinct landscapes, dendritic erosion patterns and deposited erosional remnants indicate dynamical surface processes [1,2,3,4,5,6,7]. Valleys, small-scale gullies and rounded cobbles as observed at the Huygens landing site [1] require erosion and energetic motion to be formed. There is strong evidence that liquid hydrocarbons are ponded on the surface in high-latitude lakes, predominantly, but not exclusively, at the North Pole [7,8,9]. A variety of features including extensive flows, caldera-like features, circular feature, and some channels are interpreted to be cryovolcanic in origin [10,11,12]. Chains and isolated blocks of rugged-appearing terrain found in smooth areas are best described as mountains [13] and might be related to tectonic processes. Finally, impact craters are observed but their small numbers indicate an overall very young surface [7,14,15]. In general, Titan exhibts a geologicaly very active surface indicating intense endogenic and exogenic processes. Titan‘s Morphology and Topography: The dendritic region at the Huygens site indicates an elevation of 50œ200m relative to the large darker plain. It suggests that the brighter areas within the darker terrain are higher as well. Isolated mountains and chains are subdued in some areas, with heights ≤300 m, but in other areas, including the rugged surface of Xanadu, mountain heights reach 2000 m, with slopes approaching 45° in a few cases [10]. Stereo

analysis of radar images near the largest north polar lakes indicates elevation variations ≤1200 m and slopes over 10 km baselines generally less than 5° [16]. Steep-sided depressions, some of which contain smaller lakes [3], have depths as great as 600 m [16,17]. Geological Units: Based on the spectral signature in the infrared methane windows, three major units can be distinguished: whitish material mainly distributed in the topographically high areas; bluish material adjacent to the bright-to-dark boundaries, and brownish material that correlates with dunes [15,18,19]. Although the spectral units are distinct, their compositions are not known at this time. Bright materials may consist of precipitated aerosol dust composed of methane-derived organics [19] superimposed on water-ice bedrock. The bluish component might promarily contain water ice as its defining feature [18,19]. It is no simple matter, however, to distinguish between specific organics and ices because all these molecules have comparable absorptions, resulting in similar spectral slopes. In addition, different particle sizes will have an effect on the depths of absorption bands and corresponding spectral slopes. Nevertheless, the spectral signature variations are real and indicate compositional differences and/or changes in particle sizes that are related to geological processes [6,19]. Geology at the Huygens Landing Site: Although there are no liquid hydrocarbon pools at the Huygens site, traces of once flowing liquid are obvious [1]. Surprisingly like Earth, the brighter highland regions show complex systems draining into flat, dark lowlands. Images taken after landing appear to be of a dry riverbed. If the darker region is interpreted as a dry lakebed, it is too large to have been caused by the creeks and channels visible in bright areas. It may have been created by other larger river systems or some large-scale catastrophic event, which predates deposition by the rivers seen in these images. The major elements of the Titan surface albedo variations can be interpreted to be controlled by flow of low-viscosity fluids driven by topographic variation, whether caused by precipitation as indicated by dendritic networks or spring-fed flows as indicated by stubby networks. Rounded cobbles at the site vary between 3mm in diameter, the resolution limit of the Huygens imager and a maximum of 15 cm [1]. The geology at the Huygens landing site strongly implies intense resurfacing by erosion and deposition. Tectonics and Volcanism: The driving forces of tectonics on Titan are unclear at this point; as is slso common on Earth, most of the possible tectonic features do appear to be at least partially degraded and embayed by surrounding plains units. Among the possible tectonic features are linear and ridge-like features that may be chains of hills [20]. Evidence for cryovolcanism appears in both the northern and the southern hemispheres, but it is not

ubiquitous. The most easily identified features are bright flow fronts and craters which appear to be the sources of some flows. The largest structures identified as cryovolcanic are Hotei, Tui and Ganesa Macula [10,11,21], a 180 km wide, circular feature with an apparent depression at its center and radial drainage on its sides. North of 70°N latitude is a zone of many roundish to irregular depressions that contain lakes [3]. These depressions have raised rims, deep centers, and are often nested. One possible interpretation is that they are volcanic calderas [22]. Erosional Surface Features: Titan exhibits erosional as well as depositional areas. Aeolian: The most pervasive landforms on Titan are large dune fields that extend, mostly in equatorial regions, for distances up to a few thousand kilometers [2]. The dunes are dark at radar and visible wavelengths. Their existence implies a source of particles that are distributed by winds, and a lack of nearby surface liquids to entrap them. Fluvial: Cutting across many different types of terrains are river channel systems [1,2,3,4,5,6,7]. Some channels are radar- bright suggesting that they are filled with rough boulders, others are radar-dark and may either contain liquids or have smooth deposits on their floors. Tributaries suggest that rainfall feeds the rivers, and the gentle bends, rather than tortuous sinuosity suggest that the downhill slopes are at least somewhat steep. Hence, while a cryovolcanic origin of the observed channel-like features cannot be excluded, the sharp bends and the branched networks of Titan valleys are more consistent with distributed sources than with localized sources which one would expected for cryovolcanic liquid release. Cryovolcanic flow features identified so far are also distinct from the observed branching channels [9]. Liquid methane (CH4) is suggested to be the main fluid on Titan. Liquid methane will produce turbulent flows on Titan‘s surface that have significant erosional power producing discharges and runoff production sufficient to move sediment [6,25]. Depositional: Besides dunes there are dune-free areas surrounding the bright topographically high material that might be comparable to plains as seen at the Huygens landing site [6,19]. Lakes: Abundant lakes of methane/ethane [3,8,9,26] in the northern polar region and some in the southern polar region imply the existence of an active methanological cycle and perhaps a wetter climate at the poles [3,26]. Cratering and Surface Ages: Very few impacts have been observed so far indicating, that they must be rapidly destroyed or buried by other geologic processes [7,14,18,22]. Removal of impact craters by burial and erosion is likely, given the evidence for fluvial and cryovolcanic processes, and the relatively degraded appearance of hills and ridges. The obvious lack of craters compared with other icy satellites indicates the surface of Titan is young and modified by volcanism and erosion. However, the existence of the large Menrva impact structure (>400

km in diameter) suggests that in some places larger (and thus potentially older) craters can be preserved [7,14,15,18]. Geological Evolution: One hypothesis based on an evolutionary model for Titan [27] proposes that about 0.5 billion years ago the onset of convection created high heat flow within Titan leading to a high outgassing rate for methane. Based on this assumption W ood et al., 2007 [22] speculate that the earlier terrain did not survive the tempestuous tectonics of the earlier thin crust era, and that only a few parts of the current surface are remnants of the oldest crust. In this scenario, most of the surface has formed more recently with the dune fields being the youngest.

References: [1] M .G. Tomasko et al., 2005, Nature 438, 765-778; [2] R.D. Lorenz et al., 2006, Science 312, 724-727; [3] E. Stofan et al., 2007, Nature 445, 61-64; [4] Barnes, J.W ., et al. 2007, Icarus 186, 242-258; [5] R.D. Lorenz et al., 2008, PSS in presss; [6] R. Jaumann et al., 2007, LPSC #2100; [7] C. Porco et al., 2005, Nature 434, 159-168; [8] E.P. Turtle et al., 2008, LPSC, #1952; [9] J.I. Lunine et al., 2008, LPSC, #1637; [10] C. Sotin et al., 2005, Nature 435, 786-789; [11] C. Elachi et al., 2005, Science 308, 97013; [12] R. Lopes et al., 2007, Icarus, 186, 395-412; [13] J. Radebaugh et al., 2007, Icarus 192, 77-91; [14] C. W ood et al., 2006, LPSC, #1659; [15] R.D. Lorenz et al., 2007, GRL 34, 7; ; [16] R. Kirk et al., 2008, LPSC, #2320; [17] R. Kirk et al., 2007, LPSC, #1427; [18] S. LeM ouelic, et al., 2008; JGR in press; [19] L. Soderblom, et al. (2007) PSS 55, 2025-2036; [20] R. Lopes et al., 2006, LPSC, #1347; [21] C. Elachi, et al 2005 Science 308, 970; [22] C. W ood et al., 2007, LPSC, #2118. [23] NIST 2005, Chem. W eb Book, Stand.Ref. DataBase, 69. http://webbook.nist.gov./chemistry; [24] Hanley, H.J.M ., et al., 1977, J. Phys. Chem. Ref. Data6, 597-601; [25] J.P. Perron et al., 2006, JGR 111, E11001; [26] R. Brown et al., 2008, Nature in press; [27] G. Tobie, et al., 2006 Nature 440, 61.

______Torrence V. Johnson Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA 91109

Icy Satellite Overview: 2008

The talk will assess the current state of knowledge about the icy satellites of the outer solar system that are the focus of the workshop. Much has been learned in the time since the last ISSI icy moons workshop, particularly as a result of the Cassini/Huygens mission, and the overview will focus on changes to our view of icy satellites and the new questions that have been raised by the new data. Topics covered will include: the age, origin and composition of the icy moons, geological process and energy sources, and recent discoveries in the Saturn system. This work was done at the Jet Propulsion Laboratory, California Institute of Technology under a contract from NASA.

______Kargel J.

University of Arizona

The chemistry of ices in the solar system In DATA/FACTS : Physics and chemistry of ices and organics (Tuesday afternoon)

The Solar System's volatile ices, hydrocarbons, and organics are chemically diverse. They are highly organized across the Solar System and within individual bodies in their spatial distributions in heliocentric distance, planetocentric distance, latitude, elevation, and depth. Planetary, satellite, asteroid, and comet surface conditions and interior heat flow work with the volatiles' saturation vapor pressures, pressure-melting curves, mutual solid-state and liquid-state solubilities, solid-state rheologies, and chemical reactivities (including in some places biochemical reactions and photochemical reactions) to reorganize and chemically reconstitute volatiles. Many aspects of the geology, geomorphology, and surface composition of Solar System objects are driven by recrystallization, remobilization and chemical alteration of volatiles. Many primordial nebula volatile condensates, e.g., those in unprocessed comets, are highly chemically reactive or mutually phobic, or they physically associate by van der W aals attractive forces without chemical modification; and so with even modest heating primordial volatile assemblages are modified compositionally, crystallographically, and spatially. W e may see this happening real time, billions of years delayed after initial accretion, in the jetting, outbursts, and splitting phenomena in comets. Chemical equilibria as well as volatile abundances also can be affected by differential loss of volatiles due to sequestration in cores or rocky mantles, or total loss into space. It is clear that the current inventories of volatiles on large icy moons is not the same as the assemblages first accreted. Through hydrolysis reactions and ionic solubilities, the separation of the volatile and rocky components of planetary objects is not totally clear cut. The continued volatile activity of ices and their liquids is responsible for diverse glacial, periglacial, evaporite, and other processes on Earth and Mars, and similar processes involving other volatiles are expected on icy moons. I will take three objects as examples highlighting a range of expected behavior of volatiles in the Solar System. On Earth, H2O dominates volatile cycling and illustrates some common processes in the Solar System related to phase transformations and volatile transport in solid, liquid, and vapor states. On Mars, two condensable volatile ices dominate--H2O and CO2;

these volatiles are associated to some degree in liquids and solids but also are self-segregating by their different physical and chemical properties. On Titan, a much wider variety of condensable volatiles (tholins and endogenic hydrocarbons and ices) coexist and are expected to be distributed in predictable global patterns, to interact physically and chemically, and to segregate on the surface and in the upper crust. Ammonia (and ammonium) chemistry will be presented as an example of complexity affecting ice chemistry in the Solar System

______Khurana K. Institute of Geophysics and Planetary Physics University of California at Los Angeles, CA, USA.

Saturn, Uranus and Neptune environments In DATA/FACTS : Physical constraints (Tuesday morning)

The icy satellites of the outer solar system are embedded in the field and plasma environments of the large magnetospheres. To understand the origin and evolution of the surfaces of these icy moons, a good understanding of their external environment is required. In this talk, I will review the environments of the icy satellites of Saturn, Uranus and Neptune. I will show that Saturn‘s magnetosphere is populated by the neutrals and ions of water group molecules derived from a water plume emanating from the south pole of Enceladus. I will review the properties of this plasma such as temperature, density, sonic and magnetosonic mach numbers near Enceladus, Tethys, Dione, Rhea and Titan and the expected effects on the surfaces of these moons. At the heart of the Uranian magnetosphere lies an extremely highly tilted dipole (tilt = 59°) which creates a highly warped plasma sheet near its magnetic equator. The plasma is derived mostly from the ionosphere of Uranus and is found to be close to corotation near the icy moons. Neptune‘s dipole is also highly tilted (47°) and because of the large configurational changes in the magnetosphere as Neptune rotates, the plasma sheet become bifurcated for part of a rotational period. Interestingly, the plasma appears to be derived mostly from Triton ionosphere (N+ ions) though a component derived from the atmosphere of Neptune is also present.

______Kofman W . LPG Grenoble, France

Radar investigation of icy surfaces In DATA/FACTS : Physics and chemistry of ices and organics (Tuesday morning)

Over the past decades, a number of different Synthetic Aperture Radar (SAR) techniques were developed for mapping the surface of the planets either from Earth or from orbiting spacecrafts. However, the idea to use radar to study the subsurface started to develop during about the last 15 years. The ability of the radio waves to penetrate the ice, permafrost and arid surface was at the origins of the development of the Ground Penetrating Radars (GPR). GPRs have been widely applied on Earth with a large number of the scientific and industrial applications. The application of GPR to the space exploration relies on the same operation principle but requires the development of low power and low mass equipments. The measurements from the surface cannot replace the global mapping from orbit using orbital radar sounders. MARSIS and SHARAD radars are an example of these orbital radar sounders that are now in Mars orbit and LRS in Moon orbit. These radars work essentially in the altimeter mode even if some Doppler treatment is implemented and is used in the data analysis. In this paper, we start by discussing the general electromagnetic behavior of the materials which determines the principal characteristics of the radar instrument. Then we present measurements obtained by orbital sounders and by radars used to observe Antarctica and Arctic. These results are discussed in view of its applicability to study the icy surfaces. The attainable science objectives are emphasized. W e conclude this paper by the discussion of the proposed radar payload for Laplace mission.

______Krupp N.

The jovian environment In DATA/FACTS : Physical constraints (Tuesday morning)

Jupiter with its large magnetosphere extending more than 100 planetary radii around the planet is a unique plasma laboratory. The Jovian system with the most intense radiation belts

in our solar system as well as the largest number of natural satellites of all planets is unique. Driven by the large planetary rotation the neutral and charged particle population is partially corotating with the planet essentially in a magnetodisk near the equatorial plane of the system, highly variable in density and dimension and wobbling around the magnetic axis tilted by nearly 10 degrees with respect to the rotation axis. The plasma sources of that disk are the moon Io (heavy ions Oxygen and sulfur) in the inner magnetosphere, the ionosphere of the planet (H and H3) and the solar wind (H and He) with minor components from the other larger moons in the system. In addition Io is also the major source for the dust streams throughout the Jovian system. Mass loading processes combined with exchange of matter between various regions of the magnetosphere plus field line merging and so called injections of hot plasma into the colder plasma dominate the dynamics of the system. In Jupiter's environment we have the four Galilean satellites Io (the volcanically most active body in our solar system, forming a torus of neutral and charged particles in its orbit around Jupiter), Europa (one out of three known waterworlds in the Jovian system with subsurface oceans, also having a torus along its orbit), Ganymede (the only moon with its own intrinsic magnetic field, forming a mini magnetosphere inside the large magnetosphere of Jupiter, has a subsurface ocean too), and Callisto (with a subsurface ocean too) and in total more than 60 satellites orbiting the gas giant. The study of the interaction between the corotating plasma and the moons is a wonderful tool to better understand the system as a whole as well as the surface composition of the moons, sputter and erosion processes of the surface and in their atmospheres/exospheres. In summary the environment of Jupiter is a microcosmos on its own. The understanding of the processes near Jupiter with allow to also learn more about the gas giants and their satellites found outside our solar system.

______Lainey V. IMCCE-Observatoire de Paris, UMR8028 du CNRS, 77 Av. Denfert-Rochereau, 75014 Paris, France

Tidal dissipation and orbital evolution of large satellites In ANALYSIS: Internal processes: energy sources and dynamics (Thursday morning)

Quantification of tidal dissipation is a key point to assess the past orbital evolution of large satellites. Thanks to the Galileo and Cassini missions, our knowledge of the gravity fields of

the outer planetary systems has greatly improved. This allows us to benefit of an accurate modelling when considering the orbital evolution of the satellites. In particular, the quantification of the tidal dissipation among these systems in now possible when using extended spans of astrometric observations. W e will present the up to date results concerning the estimation of the tidal dissipation and their orbital consequences for the system of Jupiter and Saturn. Some insights of the possible progresses expected from the next spacecraft missions will also be addressed.

______Lebreton J.-P. Research and Scientific Support Department, ESA/ESTEC, Keplerlaan 1, 2200 AG, Noordwijk, Netherlands. Jean-pierre.lebreton@ esa.int

Future exploration of the outer solar system

The exploration of the Outer Solar System is currently proceeding with the NASA-ESA-ASI Cassini-Huygens mission at Saturn and Titan. ESA‘s International Rosetta mission is on its 10-year journey to Comet 67P/Churyumov-Gerasimenko. NASA‘s New Horizons Pluto- Kuiper Belt mission is speeding to Pluto and beyond. NASA‘s Dawn is on its way to Ceres and Vesta. NASA‘s Juno is under development for a focused deep exploration of Jupiter during the next decade. Two exciting missions are jointly assessed by ESA and NASA as candidates for the next Outer Planet Mission (OPM): the Europa Jupiter System Mission (EJSM), with JAXA‘s participation, and the Titan Saturn System mission (TSSM). The choice as to which mission will proceed for development for launch in the 2018-2022 time frame (reference launch date 2020) is planned to be made jointly by NASA & ESA in early 2009. In ESA‘s Cosmic Vision implementation plan, the OPM will compete with two astronomy missions for approval in 2012. International collaboration plays an important role in Cassini-Huygens, Rosetta, New Horizons, Dawn, Juno, although implemented using different approaches. Hopefully, whether EJSM or TSSM becomes the next OPM, it will pave further the way for an international venture to explore Icy Moons of the two Solar System gas giants. Cassini-Huygens is well supported by Hubble Space Telescope and Ground-based observations. W ithout doubt, Earth-based observatories will continue to improve and will provide unique complementary capability to space exploration. Laboratory work and modelling efforts will also continue contributing to exploration and understanding of the outer planet worlds. Europlanet‘s efforts to promote synergy between space-based and Earth-based

observations, and laboratory work and modelling effort, is contributing to pave the way to an exciting future for the exploration of the Outer Solar System Icy W orlds.

______Lopes R. R.M.C. Lopes, K.L. Mitchell, G. Mitri (Jet Propulsion Laboratory, California Institute of Technology)

Cryovolcanism in the outer solar system: an overview In DATA/FACTS: Surface characteristics œ topography/morphology (Monday afternoon)

Cryovolcanism is a process that has no terrestrial analogue in terms of magma composition, but appears to be widespread in the outer solar system. W hen relatively high viscosity cryomagmas are involved, the morphologic characteristics of cryovolcanic features can be strikingly similar to those produced by silicate volcanism on Earth. Major unknowns at this point include composition of the cryovolcanic mixtures on various moons, dissolved volatile content, interior to surface transport, and existence of cryomagma chambers. The last two of these unknows are particularly contentious due to the apparently strong negative buoyancy of most candidate cryomagmas in icy crusts, with solid state convection considered a likely alternative to buoyancy plume rise for bringing cryomagmatic materials to the near-surface. Voyager and Galileo observations showed that relatively recent cryovolcanic activity likely occurred on Europa and Ganymede, among others, while Cassini observations showed active plumes on Enceladus that may be either cryovolcanic, or the result of more local processes akin to geysers on Earth. Several features thought to be cryovolcanic have been revealed on Titan‘s young surface. These include large flows, an eroded volcanic dome or shield, and calderas associated with flows. This talk will review cryovolcanic processes with a focus on the surface morphology of features on Titan

______Lorenz R. JHU Applied Physics Lab, Laurel, MD, USA.

Compositions of ices and volatiles in the Saturnian system: constraints from the Cassini- Huygens mission. In DATA/FACTS : Composition of the moons (Monday morning)

The pre-Cassini perspective on compositions in the Saturnian system was dominated by the known widespread presence of water ice, the known but possibly minor role of methane and its photolysis products, and the suspected role of ammonia. The formidably-instrumented Cassini spacecraft has shown us that the picture is rather more complicated, and perhaps somewhat more oxidised, than we thought. Cassini VIMS data point to the presence of CO2 ice on several satellite surfaces, as well as organics and the surprising presence of Fe2+ compounds. UVIS measurements similarly point to the presence, and variation in abundance, of non-water-ice material. RADAR and radiometry data suggest a radial gradient in composition in the Saturnian system œ radar albedos decrease systematically away from Saturn, suggesting the increase in some absorbing contaminant (metallic compounds, ammonia, tholins or nitriles.) The plumes of Enceladus have provided a striking opportunity to sense composition directly, indicating (via the INMS instrument) organics, CO2 and molecular nitrogen as well as water vapor. Cassini's CDA instrument has sampled plume and E-ring particles, indicating water and silicon compounds, as well as perhaps hints of sodium. Thus the water ice domination remains, and organics seem to be widespread, the presence and mobility of oxygen-bearing species in the Saturnian system is a surprise. Ammonia remains elusive, yet the existence of molecular nitrogen in the system, the Argon isotope ratios in Titan's atmosphere, and widespread geological activity despite low temperatures, suggests it should be present.

______M atson D. D. L. Matson1, J. C. Castillo-Rogez1, T. V. Johnson1 (1) Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA, USA (Dennis.L.Matson @ jpl.nasa.gov)

Early thermal evolution of small and mid sized icy moons in IMPLICATIONS : Evolution of the moons (Friday morning)

The discovery of geysers on Enceladus by Cassini-Huygens provided strong evidence that our knowledge of the geophysics of icy satellites was very incomplete. The data returned by Cassini has sparked a revolution in the modeling of icy satellites. Mimas and Iapetus provide other vexing puzzles. Mimas is closer to Saturn than Enceladus and given the properties of its orbit, it should be more active than Enceladus. W hy is it cold and inert? In 1966 Peale

pointed out that Iapetus should not have despun. But in fact, it is synchronously rotating about Saturn with an eighty-day period. Furthermore, its shape is that of a hydrostatic body with a period of 16 hours, indicating a faster rotation rate in the past. These and other newly available facts have motivated the ongoing reconsideration of icy satellite modeling that is (1) including more physical effects, (2) including improvements in computational techniques, and (3) highlighting the need for better knowledge of material properties relevant to the icy satellites. The relevant physics due to porosity, short-lived radioactive species, and hydrothermal processes are now being included as appropriate. Solid-state convection is probably not significant for these satellites. Simultaneous thermophysical and dynamical evolution modeling are bettering computational techniques. Now, in these models, the each property and each spatial element are updated with each computational cycle. Satellite interiors are no longer homogeneous. The modeling effort, in general, suffers from a lack of accurate properties for ice at low temperatures and for frequencies corresponding to the satellite orbital periods. Size is important. The mid-sized satellites have preserved evidence relevant to their formation and their evolutionary paths. Large satellites have evolved further and more intensely. As a consequence, much evidence relevant to their formation and evolution has been destroyed. On the other hand, the small satellites evolved little after their own formation. This is why the mid-sized moons are very interesting --- they have a history to tell. This work has been conducted at the Jet Propulsion Laboratory, California Institute of Technology, under a contract with the National Aeronautics and Space Administration. Copyright 2008 California Institute of Technology. Government sponsorship acknowledged.

______M c Cord T. B. The Bear Fight Center

Composition of the icy moons in the jovian system from observations In DATA/FACTS : Composition of the moons (Monday morning)

The large body of observational evidence for both the bulk compositions of the satellites and for the derived surface materials due to processes operating in and upon the bodies will be summarized and some conclusions suggested. The gross physical properties (size, mass, density, shape) and thermodynamic models suggest differentiated compositional structures composed of modified silicates and water to varying degrees. The amount and timing of

energy deposited and transferred within these objects varied greatly, resulting in a considerable variety of end states. Observations of the surface composition show evidence of these two main components along with materials derived from them due to internal processes, irradiation from outside and perhaps infall. Liquid water certainly was a major player in the evolution of these objects and may well still exist. Although these objects represent a suite of archetype examples of evolution of water-silicate bodies in and outside our solar system, our current knowledge is only sketchy and tantalizing. There is much to discover about these objects that could be applied to other examples, and close and sophisticated observations are the most effective way to proceed with the exploration.

______M osqueira I. SETI Institute.

Formation of the regular satellites in IMPLICATIONS : Origin of the moons (Friday morning)

W e present a brief overview of the formation of a giant planet and its associated circumplanetary disk (Estrada et al. 2008 and references therein). The formation of the subdisk straddles the stage during which the giant planet carves out a deep, well-formed gap in the solar nebula. The presence of a gap in the nebula decreases the gas inflow rate and increases its specific angular momentum, resulting in the formation of a subdisk upon inflow that is compact compared to the planetary Hill radius, but extended compared to the radial extent of the regular satellites. Following giant planet formation, planetesimals in the planet‘s feeding zone undergo a brief period of intense collisional grinding, so that a fraction of the mass of solids will be fragmented into objects smaller than a 1 km. The mass contained in planetesimal fragments in the meter to kilometer mass range can be delivered to the circumplanetary disk via inelastic or gravitational collisions taking place in the Hill sphere of the planet, or by ablation through the subnebula gas disk. The environment in which the regular satellites form is tied to the process of subnebula gas dispersal. W e advance two different satellite formation models that span the range from a gaseous (and massive compared to the mass of the regular satellites) to a gas-poor circumplanetary disk, and are based on different assumptions regarding the turbulent state of the subnebula at the time of satellite formation. Neither model relies on specific turbulence parameters, and both treat

planetesimal dynamics explicitly. W e will briefly discuss observational tests that can be used to discriminate between the two.

______Neubauer F. University of Köln (Cologne)

Electromagnetically induced magnetic fields from within the icy moons In DATA/FACTS : Physical constraints (Tuesday morning)

The analysis of magnetic fields due to electromagnetic induction in conducting volumes inside planetary bodies like the icy satellites of the outer solar system constitutes a powerful tool to observationally probe their interiors. Induced fields indicate the presence of materials of increased electric conductivity in part of the planetary interiors. High electric conductivities can be due to metallic conductivity in solid and/or liquid cores or electrolytic conduction in oceans below the surface.For induced fields to be generated there must be inducing fields applied to these bodies from the outside. W e discuss the possible sources of these inducing fields and highlight the discussion with the examples of Europa and Titan. In particular, we show that taking into account the interaction between the magnetospheres and the satellites can often strongly improve the accuracy of the diagnosis of the interiors.

______Postberg F.

Exchange processes between satellites and rings In ANALYSIS: External processes: interact. with atmosph. and space environ. (Thursday afternoon)

In my talk I would like to focus on our recent finding of sodium salts in E ring and plume grains and the implications for an Enceladus ocean as well as grain production and ejection.

______Prockter L. œ Pappalardo R.

The geology of Europa In DATA/FACTS: Surface characteristics œ topography/morphology (Monday afternoon)

Images and other data returned by the Galileo spacecraft suggest that an ocean hides beneath Europa‘s surface, linked to the icy shell through tidal deformation. A lack of large craters suggests that the average surface age is only tens of millions of years, and it is possible that geological activity persists today. The satellite hosts a variety of morphologic and tectonic features, including ridges that may be thousands of kilometers in length, pull-apart bands that result from complete separation of the lithosphere, and chaos regions, where the surface has been broken up from below by liquid or ductile material. In this paper, I will describe the morphological characteristics and stratigraphy of the wide variety of geological features on Europa, and their implications for its evolution.

______Prockter L.

Geological mapping and interpretation of icy satellite surfaces in ANALYSIS : Past and present dynamics of icy surfaces (Wednesday morning)

Geologic mapping is a technique that can yield valuable information about the surface histories and evolution of planetary bodies. Care must be taken to correctly understand the source datasets, employ appropriate map projections, and use consistent and correct unit designations, in order to provide good constraints for interpretation of other datasets. In this paper I will discuss some of the particular issues that need to be considered when mapping icy moons, and interpreting their stratigraphic histories.

______Raulin F. LISA, CNRS & Universités Paris 7 & Paris12, 61 Avenue Général de Gaulle, F-94000 Créteil, France, raulin@ lisa.univ-paris12.fr

Habitability of Titan In IMPLICATIONS : Exobiology, habitability and planetary protection (Tuesday afternoon)

The question of the possibility of Life on/in Titan is linked to two complementary questions: ‡ Could life have originated and evolved in Titan‘s environment? ‡ Is Titan‘s environment suitable to live on/in? The emergence of Life œat least as we know it - requires the availability of liquid water, organic matter and energy. On Earth, an important part of the prebiotic chemistry which allowed the formation of the first replicating macromolecules, probably occurred in the vicinity of the hydrothermal vents, in the primordial oceans. Those conditions were present on Titan during its early history. Models of formation and evolution of the satellite strongly suggest that during the first tens of millions of years after the formation of Titan, it had an aqueous ocean in direct contact with a dense and warm atmosphere, and covering a silicate bedrock. During that time, Titan could have experienced hydrothermal vents like the Earth allowing a complex organic chemistry to evolve toward life. Although we do not know how long it took on Earth for chemical evolution to go to biological evolution, it cannot be excluded that several tens of million of years is large enough for that. Then thermal evolution of Titan‘s interior produced the formation of two water ice layers, isolating the ocean from the atmosphere on one side and the rocky internal layer on the other. Thus today, prebiotic chemistry in the ocean seems much less favourable for the origin of Life. Now, if life originated on Titan, were and are now Titan‘s conditions compatible with the surviving, development and evolution of Life? Possible habitability requires several conditions: - The presence of liquid water - A source of potential nutriments (organic compounds and/or inorganic species bringing the chemical elements essential to life œ C, N, H, O, P, S and some metal ions) - An energy source to sustain the metabolic reactions.

- And environmental physical conditions compatible with the persistence of the biological systems (limits in temperature, pressure, radiation doses, pH etc). These conditions are present in Titan‘s internal ocean: ‡ liquid water: permanently, at relatively warm temperatures and with conditions of pressure and pH which are even compatible with terrestrial life. ‡ source of nutriments: organic matter, from chondritic materials, and dissolved minerals. ‡ energy: from radioactive nuclei in the deep interior and tidal energy dissipation Thus, it cannot be excluded that life œ as we know it - 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. The possibility of Life on Titan‘s surface, particularly in Titan‘s lakes, has been recently considered. This is another possibility. But it involves metabolic pathways at very low temperature, for which we have no data. References: Fortes AD (2000). Exobiological implications of a possible ammonia-water ocean inside Titan. Icarus 146, 444-452. McKay CP and Smith HD (2005). Possibilities for methanogenic life in liquid methane on the surface of Titan. Icarus 178: 274-276. Raulin F, Lunine JI, McKay C & Owen T (2008). Titan‘s astrobiology, in —Titan after Cassini- Huygens“, B. Brown et al. Eds, Univ. Arizona Press, in preparation. Schulze-Makuch D and Grinspoon DH (2005). Biologically enhanced energy and carbon cycling on Titan? Astrobiology 5, 560-567.

______Schmidt J. Jürgen Schmidt1, N.V. Brilliantov2, S. Kempf3, F. Postberg3, U. Beckmann3, F. Spahn1 1Universität Potsdam, Germany 2University of Leicester, UK 3MPI Heidelberg, Germany

Condensation and Dynamics of Ice Grains in Enceladus‘ Plume in ANALYSIS : Past and present dynamics of icy surfaces (Thursday afternoon)

In this paper we study the condensation of ice grains at Enceladus from the vapor flowing through cracks in the satellites‘ south polar ice crust, connecting pockets of liquid water at triple point conditions to vacuum.

W e derive the fluxes of such grains, and their size and speed distribution. From these we construct an average plume model (Schmidt et al, Nature, 2008) and a model for the discrete plume sources identified in images (Spitale and Porco, Nature, 2008). W e compare the plume models to CASSINI observations. W e discuss possible scenarios for the inclusion of Sodium in the grains, which was identified in mass spectra of E ring particles obtained by the Cassini Cosmic Dust Analyzer (see talk by F. Postberg et al., this conference).

______Schubert G. UCLA; John Anderson, JPL

Rhea and the diversity of outer planet icy satellites in IMPLICATIONS : Evolution of the moons (Friday morning)

Several papers have discussed the gravity data from a single flyby of Rhea. The three published gravitational fields all differ significantly. W e argue that this difference is caused by systematic error in the Cassini radio Doppler data used in the analysis. All three published fields fit the systematically corrupted data equally well. However, by restricting the data in the fit to a shorter interval surrounding the closest approach to Rhea, this systematic error can be eliminated and a reliable unbiased estimate for Rhea‘s quadrupole gravitational field is obtained. W ith this approach, and under the assumption that Rhea is in hydrostatic equilibrium, our earlier conclusions about Rhea‘s internal structure are confirmed. Rhea is an undifferentiated satellite made up of about 25% rock-metal and 75% water ice by mass. The best-fit value of the quadrupole gravitational -6 coefficient C22 from the present analysis is (267.6 ± 4.9) ×10 . Further, any assertions that Rhea is not in HE are not supported by the data. A comparison of the icy satellites of Jupiter and Saturn reveals a remarkable diversity among these objects. Bodies of similar mass, size, and silicate content differ from each other in such basic characteristics as the state of internal differentiation. Examples are the group Ganymede, Callisto, and Titan and the group Rhea, Dione, Tethys and Iapetus. Since radiogenic heating is similar for bodies in these groups their strikingly different characteristics must be attributed to either tidal heating during their thermal evolutions or short-lived radiogenic heating early in their evolutions. The possibly differentiated members of these

groups have plausibly experienced significant tidal heating in the past.

______Sotin C. Jet Propulsion Laboratory, California Institute of Technology, Mail-Stop 183-301, 4800 Oak Grove Drive, Pasadena, CA, 91109, U.S.A. Christophe.Sotin@ jpl.nasa.gov

Convective motions within icy mantles In ANALYSIS: Internal processes: energy sources and dynamics (Thursday morning)

The icy moons of the outer planets display a large variety of surface features: faults, domes, geysers, mountains, etc… In addition, geophysical data have been able to constrain the interior structure of the Galilean satellites and suggest the presence of an ocean below the ice crust of Europa, Ganynede, Callisto. By analogy with Earth, it is tempting to link the surface features to convective motions in the icy crust. Progress in the modeling of convection processes with a complex viscosity has lead to the conclusion that convective processes are likely to exist in the icy layer of the satellites. Based on these models, predictions on the interior structure can be drawn and future missions will be able to validate or deny these predictions. Is convection necessary to explain the different surface features? Are there alternative processes? After reviewing the current knowledge on convection processes, this paper describes the implications for the interior structure and gives some directions for laboratory experiments that are needed to better constrain the modeling of the internal dynamics and evolution of the icy moons. This work has been carried out at the JPL, Caltech, under contract with NASA.

______Spohn T. Tilman Spohn, DLR Insitute of Planetary Research, Berlin

Oceans in Icy Satellites In ANALYSIS: Internal processes: energy sources and dynamics (Thursday morning)

Induced magnetic fields detected by the Galileo mission at the Jovian satellites Europa, Ganymede, and Callisto have been interpreted as evidence for oceans covered by tens to a

few hundred kilometer thick ice I shells. Thermal models of these satellites have shown that oceans are feasible depending on heat transfer parameter values of the ice shells, heat production rates in the ice shells or in the deeper rocky or partly rocky interiors, and the phase diagrams of the satellite ices. (It is the anomalous behavior of ice I for which the melting decrease with pressure that makes oceans possible in the first place.) Heat transfer can be by thermal conduction and convection. For convection, the rheology of ice must be considered as well as the properties of stagnant lid convection. The latter mode of convection features thick stagnant and thermally conductive lids and temperatures in the ice underneath that tend to be higher than in the convective regions of mobile lid convection. Heat production can be by radioactive decay in the rock or by tidal heating. The phase diagram of ice needs to consider the effects of ammonia, methane, and salts on the temperature and pressure of the triple point. In addition rock in the ice shells must be considered since it will change the near surface pressure gradient in the satellite and the depths at which the triple point pressure is reached. A careful consideration of the likely values of the relevant parameters suggests that oceans may be present in many satellites including the larger satellites of Jupiter as well as Titan and Triton and medium-sized satellites such as Rhea, Titania, and Oberon. Oceans are also to be expected for Pluto and other trans-Neptunian objects (TNO's) such as 2003 UB313, Sedna, and 2004 DW . W henever oceans are sandwiched between ice shells and rocky interiors the oceans may be habitable because water and nutrients are available. This would apply to most of the satellites listed above but not to Ganymede and Callisto where the oceans are likely to be sandwiched between layers of solid ice.

______

Tobie G., M. Choukroun3, O. Grasset1,2, C. Sotin3 1University of Nantes, LPGNantes, 2CNRS, UMR 6112, 2 rue de la Houssinière, 44322 Nantes, France, 3JPL-Caltech, 4800 Oak Grove Drive, Pasadena, CA 91109, USA. Contact: gabriel.tobie@ univ-nantes.fr

Cryovolcanism : exchanges between mantle and icy crusts in ANALYSIS : Past and present dynamics of icy surfaces (Wednesday morning)

Introduction: The Galileo mission (1995-2003) and the Cassini-Huygens mission (2004- 2010) in orbit around Jupiter and Saturn, respectively, have revealed that these two giant planets host several very active moons. One of the most spectacular discovery is certainly the observation of active jets of water vapor and icy particles above Enceladus‘ south pole, which

definitely demonstrates how active icy moons can be. Many surface features, possibly of cryovolcanic origin, have also been identified on the surface of Europa [Pappalardo et al. 1999, Mével et al. 2007], Titan [Sotin et al. 2005, Lopes et al. 2007], Ganymede [Showman et al. 2004] and other moons. On Europa, the discovery of hydrated salts on its surface [Mc Cord et al. 1999] support the idea that exchanges between the internal ocean and the icy crust have occurred along Europa‘s history and is probably still occurring. On Titan, the measurements performed by the Huygens mass spectrometer [Niemann et al. 2005 provided circumstantial evidences that the atmospheric methane is recycled by internal outgassing processes associated to cryovolcanic activity, maybe still operating [Tobie et al. 2006]. On Enceladus, there is now no doubt that cryovolcanic activity, anticipated since the Voyager era [Squyres et al. 1983], is occurring and sampling of the water plumes provide a unique opportunity to probe the composition of its subsurface [W aite et al. 2006]. Even though there are more and more evidences for cryovolcanic activity on icy moons, the internal processes leading to such an activity still remains poorly constrained. Cryovolcanic flows and edifices are probably related to the rise of aqueous solutions through the icy crust, but the heat sources, the internal dynamics, and the extraction processes required to trigger a cryovolcanic event still need to be understood. In the present paper, we present and discuss some latest advances in modeling the different mechanisms associated to cryovolcanism. Heat sources. Radiogenic heating in these icy bodies is relatively low and is only concentrated in the rocky core. In the outer icy shell, only frictional heating owing to solid tides raised by their giant planet on the satellite can significantly contribute to the heat budget. Tidal heating associated with their eccentric orbit has long been suspected to play a major role in the thermal evolution of giant planet moons. The surprising activities of Io and now, of Enceladus are the most convincing evidence for tide-generated heat. The specific rheological properties of water ice make the outer shell very dissipative, and hence provide a huge source of energy. Recent progresses in the modeling of tidal dissipation permit now to better quantify the distribution of tidal dissipation and its coupling with the convective instabilities [Tobie et al. 2005a, Tobie et al.2008]. Another sources of energy is provided by the crystallization of the internal ocean. More exactly, this corresponds to the release of internal heat stored in the form of latent heat in the liquid phase during accretion and differentiation. W hen the liquid phase crystallizes, the ice shell progressively thickens and the surface heat flux rapidly increases when the layer reaches the critical thickness for the onset of convection, thus promoting cryovolcanic activity [e.g. Tobie et al. 2005b, Tobie et al. 2006].

Cryovolcanism can be sustained as long as the crystallization of the ocean and tidal dissipation provide energy in sufficient amount. Convective motions, melting and associated crustal deformation: For ice shell thicknesses larger than 20-30 km, numerous studies have suggested that solid-state convection should occur, increasing the efficiency of heat transfer and the temperature a few kilometers below the surface. As tidal dissipation is viscosity-dependent, it influences the convective instabilities. In specific conditions, the ice in hot rising plumes can be heated up to its melting point, which may result in the formation of relatively large zone of melt at the base of the lithosphere (Sotin et al. 2002, Tobie et al. 2003). Owing to their low thermal conductivities, the presence of clathrate in the crust, can also favor the increase of internal temperature and hence the occurrence of melting and clathrate dissociation. The rupture of the cold icy crust due to the combined effect of thermal and tidal stresses also favor the rise of hot materials to the surface, possibly leading to short resurfacing events. Numerical simulations of 2D thermal convection indicates that the combination of localized tidal heating, the presence of low conductivity materials (clathrate) and rupture of the lithosphere can lead to large production of cryomagmas. Cryomagma extraction and outgassing processes: Cryovolcanism on icy satellites, conversely to silicate volcanism on Earth, Venus, or Io, is subject to a major conceptual issue: the liquid water produced upon melting of ice is denser than the solid. Therefore, in the pure

H2O system, it is physically impossible to observe extrusion of a liquid on the surface of an icy shell, except if the cryomagmatic reservoir is over- pressurized owing to local stresses, topography variations or global extension [Showman et al. 2004, Manga and W ang 2007]. In absence of overpressure conditions, a cryomagmatic source must fulfill two conditions: 1) by analogy to silicate volcanism, partial melting of ice has to occur in a binary, or more complex, system; 2) the liquid produced upon melting must be less dense than solid crust materials. Owing to its anti-freezing effect, ammonia is a very good candidate as a second compound. Moreover, the density of highly concentrated ammonia-water mixtures is actually lower than that of ice Ih, as an example a 30 wt% NH3 mixture has a density lower than 920 kg.m-3 at temperatures higher than 210 K [Croft et al., 1988]. Such a highly concentrated ammonia-water mixture may be generated above a thermal upwelling plume if the icy crust contents some traces of ammonia hydrate. The rise of ammonia-rich cryomagma directly from the ocean is very highly as it would require a very high concentration in NH3 in the ocean. Another possibility is that the icy crust is significantly denser than water ice due to the presence of another heavy components, such as silicate particles, clathrates of CO2 etc. In

this condition, the rise of water-rich cryomagma would be promoted, but the long-term gravitational stability of such an icy crust would remain problematic.

The presence of dissolved gases, such as CH4, CO2, CO, SO2 etc., within the cryogenic liquids may also help the rise of the liquids if exsolution of the gas species occurs during the ascent. Owing to this process, gaseous components can be emitted on the surface. However, as the solubility of these gases is pretty low in pure water or ammonia-water solutions, the cryogenic liquids can transport only very small quantities of gas from the subsurface ocean to the surface. For Titan, for example, even if a cryomagma saturated in methane ascends up to Titan‘s surface, the emission of ~ 3x108 km3 of cryolavas is necessary in order to supply enough methane to renew the atmospheric methane abundance of ~2.8x1017 kg [Niemann et al., 2005] one time only. Such a volume would correspond to a total thickness of 3.8 km cryolavas deposited all over Titan‘s surface over the past 10-100 Ma [Choukroun, 2007; Choukroun et al., 2008], burying most of the impact craters which seems inconsistent with the first estimated crater statistics [Lorenz et al. 2008]. Conversely, massive outgassing of methane and other gas components may be induced by the ascent of ammonia-rich cryomagma through crustal reservoirs of clathrate. Indeed, ammonia significantly reduce the dissociation temperature of methane clathrate. In this condition, the destabilization of clathrate may saturate the liquids in gas, leading to the formation of gas bubbles and favoring the ascent of cryomagmas. If the bubble volume fraction becomes large enough, explosive eruption may possibly occur. Alternatively, the destabilization of crustal clathrate reservoir may also be induced In absence of cryomagma if the rupture of the lithosphere occurs. The complete crustal overturning would expose warm clathrate reservoirs onto the surface, which can liberate a significant part of their gases before cooling. Conclusion: Thermal plumes of water ice powered by tidal friction and ocean crystallization can induce melting at shallow depths. The generated cryomagmas may be extracted up to the surface if sufficient amount of ammonia hydrate is present in the crust or if the crust is enriched in heavy elements. During their ascent through the crust, cryomagmas enriched in anti-freezing components, such as ammonia, can destabilize crustal reservoirs of clathrate, leading to the emission of large quantities of gas, which in return help the rise of the cryomagmas. Even in absence of melting and generation of cryomagma, significant outgassing can occur if the rupture of the lithosphere allows the exposure of warm clathrate- rich materials onto the surface of the icy moons. References : Choukroun M . (2007), PhD Thesis, Univ. Nantes, France. ; Choukroun, M . et al. (2008). LPSC XXXIX, #1837. ; Croft, S. K. et al. (1988). Icarus, 73, 279-293. ; Lopes, R. M . C. et al. (2007). Icarus, 186, 395-412. ; M anga, M . and W ang, C. Y. (2007). Geopshysical Res. Lett.,

34, CiteID L07202. ; M cCord, T. B. et al. (1999), J. Geophys. Res., 104, 11827-11852. ; M ével L. et al. (2007). Planet. Space Sci. 55, 915- 927 ; Niemann, H. B. et al. (2005). Nature 438, 779-784. ; Pappalardo, R. T. et al. (1999). J. Geophys. Res. 104, 24015-24056. ; Showman, A. P. et al. (2004). Icarus, 172, 625-640. ; Squyres, S. W . et al. (1983). Icarus 53, 319-331. ; Sotin, C. et al. (2002). Geopshysical Res. Lett., 29, 74-1, CiteID 1233. ; Sotin, C. et al. (2005). Nature 435, 786-789. ; Tobie, G. et al. (2003). J. Geophys. Res. 108(E11), 10-1, CiteID 5124. ; Tobie, G. et al. (2005a). Icarus 177, 534-549. ; Tobie, G. et al. (2005b). Icarus 175, 496-502. ; Tobie, G. et al. (2006). Nature 440, 61-64. ; Tobie, G. et al. (2008). Icarus 196, 642-652. ; W aite, J. H. et al. (2006). Science, 311, 1419-1422.

______Tokano T. Institut für Geophysik und Meteorologie, Universität zu Köln, Germany

Surface reaction to seasonal variations in the case of Titan in ANALYSIS : Past and present dynamics of icy surfaces (Thursday afternoon)

Prior to the Cassini mission, Titan‘s rotation rate was not precisely known due to the thick haze layer, which hampered telescopic observations of surface landmarks. The synchronous or non-synchronous rotation of Titan was mainly discussed in terms of tidal dissipation. However, in contrast to all other moons in the Solar System, Titan is covered by a dense atmosphere of 1.5 bars. By analogy with the Earth, a substantial seasonal variation in the atmospheric circulation pattern should induce a periodical exchange of angular momentum between the atmosphere and surface and thus a seasonal variation in the length-of-day (LOD) of Titan‘s crust in order to conserve the total angular momentum of Titan. In the case of the Earth the seasonal variation in the LOD is merely ~1 millisecond. On the other hand, numerical modelling of Titan‘s atmospheric circulation suggest that in the case of Titan the expected annual LOD variation may amount to a few minutes, thus several orders of magnitude larger than for the Earth. The main driver of the LOD variation is the seasonal change in the atmospheric angular momentum (AAM) of the zonal wind. Titan has an obliquity of 26.7°, so the latitude of maximum surface heating shifts considerably with season. Moreover, the slow rotation of Titan inhibits the formation of large meridional temperature gradients at mid latitudes unlike on Earth. Under this condition even small seasonal temperature changes can change the zonal wind direction near the surface via thermal wind. W estward wind is prevalent in large parts of the summer hemisphere, while eastward wind predominates in the winter hemisphere. It also turns out that Titan‘s rotation rate and season-length are fortuitously in the right range to allow meteorological condition favourable for seasonal reversals of the zonal wind direction near the surface. Since the near- surface wind has the largest contribution to the AAM the seasonal wind reversal induces a

large imbalance in the AAM budget that can be equilibrated by an exchange of AAM with the surface. The temporal change in the AAM represents an atmospheric torque that manifests itself in temporal change in Titan‘s rotation rate or length-of-day (LOD). The atmospherically forced LOD variation of Titan should be much larger than that of the Earth because Titan has a substantially smaller moment of inertia given the small mass and a slow rotation (16 times slower than the Earth). The rotational response, however, should also depend on Titan‘s interior structure, which is poorly constrained. The presence or absence of a subsurface ocean and degree of gravitational coupling in the interior are supposed to have a large impact on the LOD variation. Recent radar observations by the Cassini spacecraft have indeed confirmed a substantial seasonal variation in the LOD of Titan. Depending on the yet unknown surface moment of inertia of Titan, the implied amount of exchanged AAM necessary to explain the observed shift in Titan‘s LOD varies by an order of magnitude. These geodetic observations are going to be continued during the extended Cassini mission and comparison between the modelled AAM cycle and the observed LOD variation is expected to further constrain the meteorological nature of the AAM cycle and the interior structure of Titan. This paper reviews the mechanism of angular momentum exchange in terms of meteorology and geophysics, numerical calculations, observational data and discusses differences to the Earth‘s counterpart and implication for Titan‘s meteorology and interior structure.

______Turrini D. INAF œ IFSI - Rome Exogenous versus endogenous material: the capture of Triton and irregular satellites in IMPLICATIONS : Origin of the moons (Friday morning)

Irregular satellites and Triton represent the main anomaly in the evolution of the satellite systems of the giant planets. Their dynamical features argue against the possibility they formed from circumplanetary material at the time of the formation of the giant planets and are generally accepted as indications of an external origin followed by their gravitational capture by their host planets. Irregular satellites are generally small bodies orbiting farther away from their host planets than their regular counterparts and are generally studied as a separate population on their own. However, data from the Galileo and the Cassini missions can be interpreted as indications of

mass transfer processes acting between the irregular and the regular satellites, with material in the form of dust grains migrating inward in the systems. Triton is a different case of irregular satellite, since it's one of the biggest moons in the Solar System and orbits near its host planet. Models of Triton's capture indicate that, due to its orbital distance from the planet, it could have strongly sculpted the structure of the system, removing (though collisions and dynamical destabilisation) a population of smaller, pre- existing satellites. In this talk I'll review the relevant data and discuss their implications for the comprehension of the evolution of the satellite system of the giant planets and the whole Solar System.

______Turtle E.

Enceladus In DATA/FACTS: Surface and atmosph. characteristics œspecific bodies (Monday afternoon)

Cassini−s exploration of Enceladus is truly interdisciplinary. I will present an overview of the observations of Enceladus that have been acquired by Cassini−s complementary suite of remote sensing and in situ instruments and the discoveries they have led to. In particular, I will discuss the dramatic heterogeneity of the surface geology, the surprising level of endogenic activity at Enceladus' South Pole, the plumes themselves, and the constraints Cassini's observations put on their source. I will include results from Cassini's nominal mission and the beginning of the extended mission, including a close flyby in August 2008 and (as possible) two upcoming flybys (on 9 and 31 October 2008).

______Van Hoolst T. Royal Observatory of Belgium

Rotation and libration of large icy satellites In ANALYSIS: Internal processes: energy sources and dynamics (Thursday morning)

The large satellites of the Solar System show short-periodic rotation variations around their mean synchronous rotation. The rotation variations, or librations, are due to the gravitational torque of the central planet on the a-spherical satellite. Synchronously rotating satellites take an approximately triaxial ellipsoidal form with the longest axis in the direction to the central planet and the rotation axis as the shortest axis as a result of rotation and tides. Here, we will focus on rotation variations of Europa and Titan. Librations depend on the interior structure of the satellite, in particular on the existence of an internal fluid layer like a subsurface ocean. W ithout an ocean, a satellite responds to a gravitational torque almost like a rigid body. However, with a subsurface ocean, the librations of the different internal layers of a satellite will not be equal. W e show that strong gravitational and pressure coupling exists between the layers and that rotation variations of the surface cannot be studied separately from the librations of the interior. W e discuss the possibility of using libration observations for the detection and characterization of a subsurface ocean in Europa and Titan. Besides librations with a period equal to the orbital period of Titan around Saturn, Titan‘s atmosphere also induces even larger rotation variations at seasonal timescale, which might have recently been observed from Cassini radar images. W e study the effect of Saturn's gravitational torque and torques between Titan's internal layers on the length-of-day (LOD) variations driven by the atmosphere. For the current estimate of the atmospheric torque, we obtain LOD variations of a hydrostatic Titan that are more than 50 times smaller than the observations indicate when a subsurface ocean exists and more than 100 times smaller when Titan has no ocean. Moreover, Saturn's torque causes the rotation to be slower than synchronous in contrast to the Cassini observations. Those large differences with the observations suggest that non-hydrostatic effects in Titan are important.

______Viso M .

CNES Programme Scientist for Exo/Astro Biology

Planetary protection and the icy moons of the giants planets In IMPLICATIONS : Exobiology, habitability and planetary protection (Tuesday afternoon)

The former exploratory missions in the Jovian and Saturnian systems revealed the diversity of the icy moons of these giant planets. From the data gathered, it also appears that some of them have active surface and could have, beneath an icy crust, oceans or pocket reservoirs containing mixtures of liquid water. Based on the knowledge of the microbial diversity on Earth it seems that the presence of life form cannot be ruled out as well as for some terrestrial organisms to find there an environment allowing them to proliferate. Since several space agencies are committing themselves to explore those Icy moons and that the possibility to export the terrestrial biosphere is possible, States ruling these agencies and party of the so called Outer Space treaty (Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies (U.N. document 6347 January 1967)) have the responsibility to protect the visited bodies against contamination. The Committee for Space Research (COSPAR) on the statement of the article 9 of this treaty, is recommending a planetary protection policy which applies to the activities towards these bodies. These policy is regularly updated, taking in account the most recent knowledge and the most advance technologies. The present level of planetary protection of such bodies and ways to implement it will be presented and discussed.

______W agner R.

DLR Berlin, Germany

Cratering and surface ages of icy satellites In ANALYSIS: External processes: interact. with atmosph. and space environ. (Thursday afternoon)

Since 1995, new imaging data have been obtained from the icy satellites of Jupiter and Saturn. Between 1995 and 2003, the Galileo spacecraft was in orbit about Jupiter and returned images

of the icy Galilean satellites Europa, Ganymede and Callisto. Since June 2004, the Cassini spacecraft is orbiting Saturn and the remote sensing instruments aboard Cassini, including the wide angle (W AC) and narrow angle (NAC) cameras are returning large volumes of data from the major icy satellites of Saturn, including cloud-covered Titan. In order to shed light on the specific geologic histories of each satellite, ages of geologic units must be known. For want of radiometric data of surface materials, ages can only be obtained by measuring the frequencies of craters superimposed on these geologic units. However, translating crater frequencies into absolute ages is highly model-dependent. Impact cratering chronology models depend on the impactor population whose members preferentially bombarded the icy satellites in the outer solar system. Candidate impactor populations are (1) Jupiter Family Comets (JFCs), (2) Main Belt Asteroids (MBAs), and (3) Kuiper Belt Objects (KBOs). Based on these impactor families and their possible impact rates with time, different groups of investigators derived several chronology models which yield highly divergent cratering model ages for the same geologic unit. In this presentation, these models are compared and the pro's and con's for each model are discussed.