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Full list of authors: Blanc, Michel; Prieto-Ballesteros, Olga; André, Nicolas; Gomez-Elvira, Javier; Jones, Geraint; Sterken, Veerle; Desprats, William; Gurvits, Leonid I.; Khurana, Krishan; Balmino, Georges; Blöcker, Aljona; Broquet, Renaud; Bunce, Emma; Cavel, Cyril; Choblet, Gaël; Colins, Geoffrey; Coradini, Marcello; Cooper, John; Dirkx, Dominic; Fontaine, Dominique; Garnier, Philippe; Gaudin, David; Hartogh, Paul; Hussmann, Hauke; Genova, Antonio; Iess, Luciano; Jäggi, Adrian; Kempf, Sascha; Krupp, Norbert; Lara, Luisa; Lasue, Jérémie; Lainey, Valéry; Leblanc, François; Lebreton, Jean-Pierre; Longobardo, Andrea; Lorenz, Ralph; Martins, Philippe; Martins, Zita; Marty, Jean-Charles; Masters, Adam; Mimoun, David; Palumba, Ernesto; Parro, Victor; Regnier, Pascal; Saur, Joachim; Schutte, Adriaan; Sittler, Edward C.; Spohn, Tilman; Srama, Ralf; Stephan, Katrin; Szegő, Károly; Tosi, Federico; Vance, Steve; Wagner, Roland; Van Hoolst, Tim; Volwerk, Martin; Wahlund, Jan-Erik; Westall, Frances; Wurz, Peter, Europa is the closest and probably the most promising target to search for extant life in the Solar System, based on complementary evidence that it may fulfil the key criteria for habitability: the Galileo discovery of a sub-surface ocean; the many indications that the ice shell is active and may be partly permeable to transfer of chemical species, biomolecules and elementary forms of life; the identification of candidate thermal and chemical energy sources necessary to drive a metabolic activity near the ocean floor. In this article we are proposing that ESA collaborates with NASA to design and fly jointly an ambitious and exciting planetary mission, which we call the Joint Europa Mission (JEM), to reach two objectives: perform a full characterization of Europa's habitability with the capabilities of a Europa orbiter, and search for bio-signatures in the environment of Europa (surface, subsurface and exosphere) by the combination of an orbiter and a lander. JEM can build on the advanced understanding of this system which the missions preceding JEM will provide: Juno, JUICE and Europa Clipper, and on the Europa lander concept currently designed by NASA (Maize, report to OPAG, 2019). We propose the following overarching goals for our Joint Europa Mission (JEM): Understand Europa as a complex system responding to Jupiter system forcing, characterize the habitability of its potential biosphere, and search for life at its surface and in its sub-surface and exosphere. We address these goals by a combination of five Priority Scientific Objectives, each with focused measurement objectives providing detailed constraints on the science payloads and on the platforms used by the mission. The JEM observation strategy will combine three types of scientific measurement sequences: measurements on a high-latitude, low-altitude Europan orbit; in-situ measurements to be performed at the surface, using a soft lander; and measurements during the final descent to Europa's surface. The implementation of these three observation sequences will rest on the combination of two science platforms: a soft lander to perform all scientific measurements at the surface and sub-surface at a selected landing site, and an orbiter to perform the orbital survey and descent sequences. We describe a science payload for the lander and orbiter that will meet our science objectives. We propose an innovative distribution of roles for NASA and ESA; while NASA would provide an SLS launcher, the lander stack and most of the mission operations, ESA would provide the carrier-orbiter-relay platform and a stand-alone astrobiology module for the characterization of life at Europa's surface: the Astrobiology Wet Laboratory (AWL). Following this approach, JEM will be a major exciting joint venture to the outer Solar System of NASA and ESA, working together toward one of the most exciting scientific endeavours of the 21st century: to search for life beyond our own planet. © 2020, The authors received support from the sponsors of their home institutions during the development of their projects, particularly at the two institutes leading this effort: at IRAP, Toulouse, MB and NA acknowledge the support of CNRS, University Toulouse III - Paul Sabatier and CNES. At CAB, Madrid, OPB and JGE acknowledge the support of INTA and Spanish MINECO project ESP2014-55811-C2-1-P and ESP2017-89053-C2-1-P and the AEI project MDM-2017-0737 Unidad de Excelencia "Maria de Maeztu". We would also like to extend special thanks to the PASO of CNES for its precious assistance and expertise in the design of the mission scenario.

The search for traces of past Martian life is directly connected to ancient paleolakes, where ponding water or low-energy water fluxes were present for long time intervals. The Eridania paleolakes system, located along the 180° meridian, is one of the largest lacustrine environments that were once present on Mars. Morphological features suggest that it was constituted by connected depressions filled by water to maximum depths of ∼2400 m and a volume of at least 562,000 km3. We focused our attention on the northern side of the Eridania Basin, where high-albedo, uneven patches of material characterized by the absence of dust are present. Based on OMEGA and CRISM orbital imaging spectroscopy data, a large clay-bearing unit has been identified there. In particular, a set of aqueous minerals in present in the stratigraphy, being visible through erosional windows in the first several tens of meters of the sedimentary sequence. Below this capping unit, a thin Al-rich clay stratum attributable to Al-smectite and/or kaolins is present. This overlies a Fe-rich clay stratum, attributable to the nontronite smectite. At the base of the mineralogic sequence a stratum that could be either a zeolite or more likely a hydrated sulfate is present. In addition, small deposits of alunite (a rare phase on Mars), and jarosite are here found at several locations. Such stratigraphy is interpreted as originating from a surface weathering process similar to terrestrial abiotic pedogenesis; nonetheless, possible exobiologic processes can be also invoked to explain it. NASA's Spirit rover landed on Gusev crater in 2004, near the mouth of the Ma'adim Vallis, which connects this crater with the considered paleolakes system. The Eridania site provides the unique opportunity to complete the measurements obtained in Gusev crater, while investigating the exposed mineralogical sequence in its depositionary setting. In addition, the extremely favorable landing parameters, such as elevation, slope, roughness, rock distribution, thermal inertia and dust coverage, support this location as a possible landing site for the NASA Mars 2020 rover.

When looking for traces of past life on Mars, we have to look primarily for places where water was present, possibly for long time intervals. The Simud and Tiu Valles are two large outflow channels connected to the north with the Chryse Basin, Oxia Palus quadrangle. The area, carved by water during the Noachian/Early Hesperian is characterized by a complex geological evolution. The geomorphological analysis shows the presence of fluvial and alluvial structures, interpreted as fluvial channels and terraces, debris flow fronts and short-lasting small water flows coexisting with maar-diatremes and mud volcanoes. Several morphological features indicate a change in water flux direction after the main erosive phase. During this period water originated from the Masursky crater and flown southwards into the Hydraotes Chaos. This phenomenon caused the studied area to become a depocenter where fine-grained material deposition took place, possibly in association with ponding water. This setting is potentially quite valuable as traces of life may have been preserved. The presence of water at various times over a period of about 1 Ga in the area is corroborated by mineralogical analyses of different areas that indicate the possible presence of hydrated minerals mixtures, such as sulfate-bearing deposits. Given the uniqueness of the evolution of this region, the long term interactions between fluvial, volcanic, and tectonic processes and its extremely favorable landing parameters (elevation, slope, roughness, rock distribution, thermal inertia, albedo, etc.), we decided to propose this location as a possible landing site for the ESA ExoMars 2018, the NASA Mars 2020 and future on-site missions.

We present a steady state hydraulic model of the tributary and the outlet of a Martian paleolake located in the Memnonia quadrangle between 167°0'0''W and 167°30'0''W longitude and between 9°25'0''S and 9°45'0''S latitude. The Mars Express High-resolution stereo camera (HRSC) digital elevation model, H31850000DA4, with a spatial resolution of 75 m is used to describe the geometrical features of the hydraulic system. A steady state hydraulic model, through a Monte Carlo procedure, is adopted to investigate the assumption that the tributary-lake-outlet hydraulic system was acting simultaneously during its last water-related evolutionary phase. Through our analysis, we infer the roughness coefficient and the discharge of both the tributary and the outlet channels. Geomorphic evidence, such as river terraces, were used to constrain the water discharge and the Manning's roughness coefficient, thereby obtaining estimates of the water level in the lake, during the last evolutionary phase of the system. Our analysis of the outlet reveals a median paleodischarge of 7135 m3 s−1 and a median Manning's roughness coefficient of 0.067 m−1/3 s. Tributary analysis provides a median flow and a median roughness coefficient of 6405 m3 s −1 and 0.123 m−1/3 s, respectively. Moreover, the hydraulic analysis suggests that the paleolake water surface level was −1397 m (median value, HRSC elevation), which is consistent with the observed paleoshoreline. The results imply that the tributary, the lake, and the outlet were hydraulically synchronized, therefore confirming the presence of a connected water system. This study demonstrates that hydraulic analysis can provide valuable information regarding ancient Martian water fluxes.

After 40 years from the first lunar missions, Europe has startedfor the first time the development of a mission which has the Moonas a target. SMART-1 will be the first Western-European mission tothe Earth's satellite. The primary objective of the mission is toflight test technology innovation for the future scientificdeep-space missions. This paper describes the mission concept, thetechnology and the scientific aspects.

The impacts of Large Near-Earth Objects (NEOs) on Earth could trigger a global catastrophe. Even relatively small objects are capable of causing large local damage, either directly or in combination with other phenomena i.e. the large waves known as tsunamis. This paper describes the interest of dedicated space missions performing NEO discovery, monitoring and characterisation in order to assess the real magnitude of this hazard. This interest had been established by previous theoretical work; however, until now the full range of NEO space systems had not been explored in the scope of a single activity. In order to have a deeper insight into this matter the European Space Agency (ESA) issued a call for proposals for dedicated NEO payloads or NEO missions. Following selection by a panel of recognised experts six independent teams carried out parallel studies for half a year into preliminary mission analysis and design that were completed in January 2003. The rational behind these missions is discussed here.

After 40 years from the first lunar missions, Europe has started for the first time the development of a mission which has the Moon as a target. SMART-1 will be the first Western-European mission to the Earth’s satellite. The primary objective of the mission is to flight test technology innovation for the future scientific deep-space missions. This paper describes the mission concept, the technology and the scientific aspects.

The effects of the amount of sodium ions, their solar angles correlation, temperature and velocities, have been explained as consequences of the almost full penetration of the second mode of micrometeorite fluxes (M>10−8 g) across the Io atmosphere to its surface, whereas volcanism may satisfy only the amount of sodium.

An outstanding result of the Viking mission has been the detection of water vapor in the martian environment. The only possible reservoir for the water, where no evidence of surface frost has been detected, is the soil. Comparative morphologic analyses of periglacial terrestrial and martian terrains suggested that permafrost can play an important role in forming many surficial structures as the Valles Marineris landslides or the collapse structures in the volcanic region of Tharsis. In this paper a study of the thermodynamics which regulate the processes of thawing and freezing of the layers of permafrost on Mars has been carried out. The equation of the heat propagation has been solved under martian conditions both in the case of periodic variations of the surface temperature and in the case of an anomalous heating of the ground. Seasonal temperature variations do not allow survival of CO2 or clathrate permafrost down to a depth of 15 m. We have demonstrated the existence of a secular ‘active layer’ of about 100-m depth.