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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2010.05.027 Byline: Felipe Gomez (a), Eva Mateo-Marti (a), Olga Prieto-Ballesteros (a), Jose Martin-Gago (a), Ricardo Amils (a)(b) Keywords: Mars; Mars, Surface; Astrobiology; Regoliths Abstract: Current surface conditions (strong oxidative atmosphere, UV radiation, low temperatures and xeric conditions) on Mars are considered extremely challenging for life. The question is whether there are any features on Mars that could exert a protective effect against the sterilizing conditions detected on its surface. Potential habitability in the subsurface would increase if the overlaying material played a protective role. With the aim of evaluating this possibility we studied the viability of two microorganisms under different conditions in a Mars simulation chamber. An acidophilic chemolithotroph isolated from Rio Tinto belonging to the Acidithiobacillus genus and Deinococcus radiodurans, a radiation resistant microorganism, were exposed to simulated Mars conditions under the protection of a layer of ferric oxides and hydroxides, a Mars regolith analogue. Samples of these microorganisms were exposed to UV radiation in Mars atmospheric conditions at different time intervals under the protection of 2 and 5mm layers of oxidized iron minerals. Viability was evaluated by inoculation on fresh media and characterization of their growth cultures. Here we report the survival capability of both bacteria to simulated Mars environmental conditions. Author Affiliation: (a) Centro de Astrobiologia (CSIC-INTA), Carretera de Torrejon-Ajalvir, Km 4, Torrejon de Ardoz, 28850 Madrid, Spain (b) Centro de Biologia Molecular Severo Ochoa (UAM-CSIC), Universidad Autonoma de Madrid, Cantoblanco, 28049 Madrid, Spain Article History: Received 11 August 2009; Revised 14 May 2010; Accepted 28 May 2010

Several substances besides water ice have been detected on the surface of Europa by spectroscopic sensors, including C[O.sub.2], S[O.sub.2], and [H.sub.2]S. These substances might occur as pure crystalline ices, as vitreous mixtures, or as clathrate hydrate phases, depending on the system conditions and the history of the material. Clathrate hydrates are crystalline compounds in which an expanded water ice lattice forms cages that contain gas molecules. The molecular gases that may constitute Europan clathrate hydrates may have two possible ultimate origins: they might be primordial condensates from the interstellar medium, solar nebula, or jovian subnebula, or they might be secondary products generated as a consequence of the geological evolution and complex chemical processing of the satellite. Primordial ices and volatile-bearing compounds would be difficult to preserve in pristine form in Europa without further processing because of its active geological history. But dissociated volatiles derived from differentiation of a chondritic rock or cometary precursor may have produced secondary clathrates that may be present now. We have evaluated the current stability of several types of clathrate hydrates in the crust and the ocean of Europa. The depth at which the clathrates of S[O.sub.2], C[O.sub.2], [H.sub.2]S, and C[H.sub.4] are stable have been obtained using both the temperatures observed in the surface [Spencer, J.R., Tamppari, L.K., Martin, T.Z. Travis, L.D., 1999. Temperatures on Europa from Galileo photopolarimeter-radiometer: Nighttime thermal anomalies. Science 284, 1514-1516] and thermal models for the crust. In addition, their densities have been calculated in order to determine their buoyancy in the ocean, obtaining different results depending upon the salinity of the ocean and type of clathrate. For instance, assuming a eutectic composition of the system MgS[O.sub.4]-[H.sub.2]O for the ocean, C[O.sub.2], [H.sub.2]S, and C[H.sub.4] clathrates would float but S[O.sub.2] clathrate would sink to the seafloor: an ocean of much lower salinity would allow all these clathrates to sink, except that C[H.sub.4] clathrate would still float. Many geological processes may be driven or affected by the formation, presence, and destruction of clathrates in Europa such as explosive cryomagmatic activity [Stevenson, D.J., 1982. Volcanism and igneous processes in small icy satellites. Nature 298, 142-144], partial differentiation of the crust driven by its clathration, or the local retention of heat within or beneath clathrate-rich layers because of the low thermal conductivity of clathrate hydrates [Ross, R.G., Kargel, J.S., 1998. Thermal conductivity of Solar System ices, with special reference to martian polar caps. In: Schmitt, B., De Berg, C., Festou, M. (Eds.), Solar System Ices. Kluwer Academic, Dordrecht, pp. 33-62]. On the surface, destabilization of these minerals and compounds, triggered by fracture decompression or heating could result in formation of chaotic terrain morphologies, a mechanism that also has been proposed for some martian chaotic terrains [Tanaka, K.L., Kargel, J.S., MacKinnon, D.J., Hare, T.M., Hoftman, N., 2002. Catastrophic erosion of Hellas basin rim on Mars induced by magmatic intrusion into volatile-rich rocks. Geophys. Res. Lett. 29 (8); Kargel, J.S., Prieto-Ballesteros, O., Tanaka K.L., 2003. Is clathrate hydrate dissociation responsible for chaotic terrains on Earth, Mars, Europa, and Triton? Geophys. Res. 5. Abstract 14252]. Models of the evolution of the ice shell of Europa might take into account the presence of clathrate hydrates because if gases are vented from the silicate interior to the water ocean, they first would dissolve in the ocean and then, if the gas concentrations are sufficient, may crystallize. If any methane releases occur in Europa by hydrothermal or biological activity, they also might form clathrates. Then, from both geological and astrobiological perspectives, future missions to Europa should carry instrumentation capable of clathrate hydrate detection. Keywords: Ices; Europa; Geological processes; Satellite surfaces; Mineralogy

The complex geology of Europa is evidenced by many tectonic and cryomagmatic resurfacing structures, some of which are 'painted' into a more visible expression by exogenic alteration processes acting on the principal endogenic cryopetrology. The surface materials emplaced and affected by this activity are mainly composed of water ice in some areas, but in other places there are other minerals involved. Nonice minerals are visually recognized by their low albedo and reddish color either when first emplaced or, more likely, after alteration by Europan weathering processes, especially sublimation and alteration by ionizing radiation. While red chromophoric material could be due to endogenic production of solid sulfur allotropes or other compounds, most likely the red substance is an impurity produced by radiation alteration of hydrated sulfate salts or sulphuric acid of mainly internal origin. If the non-ice red materials or their precursors have a source in the satellite interior, and if they are not merely trace contaminants, then they can play an important role in the evolution of the icy crust, including structural differentiation and the internal dynamics. Here we assume that these substances are major components of Europa's cryo/hydrosphere, as some models have predicted they should be. If this is an accurate assumption, then these substances should not be neglected in physical, chemical, and biological models of Europa, even if major uncertainties remain as to the exact identity, abundance, and distribution of the non-ice materials. The physical chemical properties of the ice-associated materials will contribute to the physical state of the crust today and in the geological past. In order to model the influence of them on the thermal state and the geology, we have determined the thermal properties of the hydrated salts. Our new lab data reveal very low thermal conductivities for hydrated salts compared to water ice. Lower conductivities of salty ice would produce steeper thermal gradients than in pure ice. If there are salt-rich layers inside the crust, forming salt beds over the seafloor or a briny eutectic crust, for instance, the high thermal gradients may promote endogenic geological activity. On the seafloor, bedded salt accumulations may exhibit high thermochemical gradients. Metamorphic and magmatic processes and possible niches for thermophilic life at shallow suboceanic depths result from the calculated thermal profiles, even if the ocean is very cold. Keywords: Europa; Experimental techniques; Geological processes; Satellites of Jupiter; Thermal histories

Water ice, hydrated salts, and other volatile ices such as carbon dioxide (CO2), have been detected by spectroscopy on Europa’s surface. Although the presence of other candidate compounds like clathrate hydrates have not yet been observed on the moon, the existence of water and carbon dioxide combined with low temperature and relatively high cryostatic pressure in the interior of the planetary body, favors their occurrence. In this study, the evolution of the H2O–MgSO4–CO2 system as a function of temperature, pressure and high salt concentration was investigated, focusing especially on the differences between the resulting mineral parageneses. CO2-clathrate formation and dissociation were examined by Raman spectroscopy in the presence of other hydrated phases crystallized from aqueous solutions rich in magnesium sulfate (MgSO4) at several concentrations (5, 17 and 30wt%) from 268 to 290K and pressures up to 60bar. The CO2-clathrate experimental equilibrium line in this salty system is presented for both gas and liquid CO2 stability fields. During the heating process, the mineral assemblage of the system evolved differently depending on the salt concentration. At subsaturation (5wt% of MgSO4), the CO2-clathrate co-existed with water ice from 268 to 272K. However, when the initial sulfate concentration was 17wt%, at a temperature above 269K, no mineral phase was stable apart from CO2-clathrate. If the salt concentration of the system was supersaturated (30wt%), CO2-clathrate co-existed with meriadianiite (MgSO4·11H2O) from 269 to 275K. Subsequently, meridianiite was transformed into epsomite (MgSO4·7H2O) and continued crystallizing until 300K. The evolution of the supersaturated solution at different heating rates was also evaluated in detail. In experiments with the fastest heating, the epsomite was not stabilized and the resulting aqueous solution became more concentrated than initially, promoting a clathrate dissociation at lower temperatures than expected. Volume changes due to mineral transformations and partial/total melting processes were assessed for the system and applied to Europa’s geology. Thus, assuming that this system is present in Europa’s interior, the evolution of the presumed fluids and mineral assemblages may have resulted in the generation of local stresses promoting resurfacing. Depending on the initial composition of the system, the percentage of volume change would imply a chaotic terrain formation, or cause faulting. [ABSTRACT FROM AUTHOR]

Abstract: Planned future exploration missions to the Jovian satellite Europa have a strong astrobiological motivation. Characterization of the potential habitability of the liquid water environments, and searching for life signals are the main astrobiological objectives of these missions. To meet these objectives specific strategies and instrumentation are required. Here we discuss some scenarios for the development of Europa potential biospheres. These scenarios are based on assumptions of the life similarity concept and knowledge about terrestrial life in extreme environments. Since the potential habitable environments on Europa are in the interior of the satellite it is not possibly to directly detect life. However, there are processes that link aqueous sub-surface environments with the near-surface environment, such as tectonism or magmatism. Therefore, by analysing endogenous materials that arise from the interior it is possible to make predictions about what is in the sub-surface. We propose some measurements and instrumentation for future missions to detect biosignatures on the upper layers of Europa, including the simple physico-chemical traces of metabolism to complex biomolecules or biostructures. Raman spectroscopy or biosensor technologies are the future for in situ exploration of the Solar System. [Copyright &y& Elsevier]

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. • In this article we are proposing that ESA collaborates with NASA to design and fly jointly an ambitious planetary mission: the Joint Europa Mission (JEM). • The JEM observation strategy will combine three types of scientific measurement sequences. • The implementation of these three observation sequences will rest on the combination of two science platforms. • 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. [ABSTRACT FROM AUTHOR]

The Martian Moons eXploration (MMX) mission by the Japan Aerospace Exploration Agency, JAXA, will explore the Martian moons Phobos and Deimos. In addition to investigating the moons remotely and returning samples from Phobos, MMX will also deliver a small (about 25 kg) Rover to the surface of Phobos. The payload of the Rover consists of four scientific instruments: RAX, a Raman spectrometer to measure signatures of the mineralogical composition of the surface material, NavCam, a stereo pair of cameras to investigate the terrain and allow for navigation, miniRAD a radiometer to measure the surface brightness temperature of both, regolith and rocks, and two WheelCams which will observe the wheel-surface interface, and thus investigate the properties and dynamics of the regolith. The cameras, will serve both, technological and scientific needs. The rover will be deployed during the rehearsal phase of the landing operations for the main spacecraft and will thus land in proximity to the first sampling area. During its operational lifetime on Phobos (about 100 days), the in-situ measurements performed with the rover payload will provide scientific context for the returned samples, provide ground truth, study the surface heterogeneity and obtain information on the physical properties of undisturbed surface material. The MMX launch is planned for September 2024 and the Rover delivery is scheduled for 2027. The Rover is a contribution by the Centre National d'Etudes Spatiales (CNES) and the German erospace Center (DLR) with additional contributions from INTA (Spain) and JAXA. • In this paper we give an overview of the rover, which will be part of the MMX mission to Phobos. • The MMX rover will explore the surface of Phobos with cameras, a Raman spectrometer and a radiometer. • Scientific objectives and the mission outline are discussed. [ABSTRACT FROM AUTHOR]

Planetary protection enables scientific return from solar system bodies investigations and at the same time protects life on Earth. As we continue to explore our solar system by landing machines and humans on other planets, we need to ascertain that we do not bring potentially dangerous material home to Earth or carry anything from Earth that may contaminate another planetary body and prevent scientific investigations. A Planetary Protection Policy has been developed by the Committee on Space Research (COSPAR), which provides a forum for international consultation in the area of space research. The COSPAR Planetary Protection Policy, and its associated requirements, is not legally binding under international law but is an agreed standard with implementation guidelines for compliance with Article IX of the Outer Space Treaty. States Parties to the Outer Space Treaty are responsible for national space activities under Article VI, including the activities of governmental and non-governmental entities. The current members of the COSPAR Panel on Planetary Protection are representatives from national space agencies and thematic experts from the science community of different countries (https://cosparhq.cnes.fr/scientific-structure/ppp). Other stakeholders, including the private sector, are invited to attend and present at the PPP meetings. The COSPAR PPP maintains and updates the COSPAR Planetary Protection Policy regularly, always reviewing all available scientific knowledge leading to updates to the policy, in particular as concerns the outer solar system and lunar exploration. Such updates are performed in a careful and balanced way to ensure that the right measures are envisaged to fulfil the rationales for planetary protection. • Planetary protection enables scientific space exploration and protects the Earth. • A Planetary Protection Policy has been developed by the Committee on Space Research. • It is an agreed international standard with guidelines for compliance with the OS Treaty. • It is based on the most recent scientific knowledge. • A COSPAR Panel maintains and promotes updates to the Planetary Protection Policy. [ABSTRACT FROM AUTHOR]

Abstract: This paper reviews the utility of analog environments in preparations for a Europa lander mission. Such analogs are useful in the demonstration and rehearsal of engineering functions such as sample acquisition from an icy surface, as well as in the exercise of the scientific protocols needed to identify organic, inorganic and possible biological impurities in ice. Particular attention is drawn to Antarctic and Arctic analog sites where progress in these latter areas has been significant in recent years. [Copyright &y& Elsevier]

High-accuracy wavelength calibration is critical for qualitative and quantitative spectroscopic measurements. Many spectrometers employed in planetary-exploration missions have onboard calibration sources, including standard lamps and calibration targets. However, such calibration sources are not always available because planetary missions, particularly landing missions, usually have limitations in size and mass. Thus, a wavelength calibration method without requiring hardware addition can be highly beneficial. In this study, we demonstrate a method for wavelength calibration using solar Fraunhofer lines observed in the reflectance spectra of planetary surfaces. Using a Raman spectrometer prototype developed for a Phobos rover, we measured the spectrum of the sunlight reflected from a spectral standard, manufactured to provide similar reflectance spectra to the surface of Phobos. We identified 35 Fraunhofer absorption lines in the wavelength range between 530 and 700 nm and utilized these features for the wavelength calibration of the spectrometer. This approach using Fraunhofer lines achieved good results (better than +0.04/−0.06 nm), comparable to the results achieved using a conventional Ne lamp. The wavelength accuracy corresponds to a wavenumber accuracy better than ±1.5 cm−1 in the 0–4000 cm−1 Raman shift (Stokes shift) range with a 532 nm excitation laser. This result enabled the estimation of the magnesium number (Mg#) of olivine, achieving a value more precise than 1.5% based on the Raman peak positions. In addition, we examined the number of solar Fraunhofer lines detectable at different wavelength resolutions by binning the solar spectrum acquired in this study. We found that more than 10 Fraunhofer lines could be detected as prominent absorption lines when the wavelength resolution is higher than 1 nm/pix (30 cm−1/pix at 1000 cm−1). This result suggests that the target-free wavelength-calibration method using solar Fraunhofer lines can be applied to other spectrometers simply by observing sunlit planetary surfaces. • Method for spectrometer wavelength calibration without onboard source was developed. • Calibration uses solar Fraunhofer lines in the reflectance spectra of planetary surfaces. • An accuracy of 0.1 nm was achieved, assuring that minerals such as olivines can be subclassified with Raman spectroscopy. • Spectrometer of 1 nm/pix resolution could use 10 Fraunhofer lines for calibration. [ABSTRACT FROM AUTHOR]

Research interest in NH 4 -smectites in planetology is increasing after the discovery of their high abundance on the surface of Ceres. This dwarf planet is considered a relic ocean world, showing evidence of extended aqueous alteration and cryovolcanic activity that occurred during the course of its history (De Sanctis et al., 2020). Despite the position of Ceres in the asteroid belt, a variety of ammonium-rich minerals, including phyllosilicates, carbonates, and chlorides, have been reported on its surface (Raponi et al., 2019). Ammonium-rich phases are expected to be found at greater distances from the Sun. Consequently, the study of the stability of ammonium-bearing phases such as smectites under environmental conditions relevant to the interior of Ceres and its regolith can help elucidate certain ambiguities concerning the provenance of its precursor materials. In this study, smectites were characterized by Raman and infrared spectroscopy, X-ray diffraction, and scanning electron microscopy under conditions mimicking the surface environment of Ceres, that is, at low temperatures (110–145 K) and near-vacuum conditions (1–0.001 Pa). When NH 4 -montmorillonite was freeze-dried, different structural stabilities were observed depending on the aggregation texture of the sample. In case the clay minerals on the surface of Ceres have an endogenic origin, its chemical composition and predominant interlayer cation are expected to provide insights into the type of fluids and chemical reactions that occur at deeper layers of the icy crust. The results of this characterization study are relevant for the future selection of payloads for space missions. The strength of combining different analytical methods in characterizing and interpreting mineralogical composition has been demonstrated in this study. [Display omitted] • Characterization of NH 4 -montmorillonite coexisting with NH 4 Cl salt. • Combination of Raman, Mid/Near-Infrared spectroscopies, XRD, and SEM/EDX data. • Data obtained at low temperature and high vacuum conditions. • Planetological implications for regolith on Ceres. [ABSTRACT FROM AUTHOR]