Abstract. The Curiosity rover discovered fine--grained sedimentary rocks, inferred to represent an ancient lake, preserve evidence of an environment that would have been suited to support a Martian biosphere founded on chemolithoautotrophy. This aqueous environment was characterized by neutral pH, low salinity, and variable redox states of both iron and sulfur species. C, H, O, S, N, and P were measured directly as key biogenic elements, and by inference N and P are assumed to have been available. The environment likely had a minimum duration of hundreds to tens of thousands of years. These results highlight the biological viability of fluvial--lacustrine environments in the post--Noachian history of Mars.

X-ray diffraction analysis of the Rocknest scoop sample is described in (23); similar analyses were performed for John Klein and Cumberland. John Klein and Cumberland were the first two drill samples collected by Curiosity. All scooped or drilled samples pass through the Collection and Handling for In situ Martian Rock Analysis (CHIMRA) sample collection and processing system (10). All powders for X-ray diffraction are processed through a 150-m sieve before delivering a portion to the CheMin inlet funnel.The sieved drill powders were placed into sample cells with 6 μm thick Mylar® windows. Mylar® contributes a minor, broad scattering signature in diffraction patterns that is generally "swamped" by diffraction from the loaded sample. In addition, an aluminized light shield also contributes "peaks" to the observed diffraction patterns. Only ~10 mm 3 of material is required to fill the active volume of the sample cell, which is a disc-shaped volume 8 mm in diameter and 175 m thick. A collimated ∼70 μm diameter X-ray beam illuminates the center of the sample cell. A piezoelectric vibration system on each cell pair shakes the material during analysis, causing grains in the cell to pass through the X-ray beam in random orientations.CheMin measures XRD and XRF data simultaneously using Co radiation in transmission geometry (11). The instrument operates in single-photon counting mode so that between each readout the majority of CCD pixels are struck by either a single X-ray photon or by no photons. In this way, the system can determine both the energy of the photons striking the CCD (XRF) and the two-dimensional (2-D) position of each photon (XRD). The energy and positional information of detected photons in each frame are summed over repeated 10-sec measurements into a "minor frame" of 30 min of data (180 frames). The 2-D distribution of Co K X-ray intensity represents the XRD pattern of the sample. Circumferential integration of these rings, corrected for arc length, produces a conventional 1-D XRD pattern. For conversion of the 2-D CCD pattern to a 1-D pattern we have used FilmScan © software from Materials Data, Inc.CheMin generally operates for only a few hours each night, when the CCD can be cooled to its lowest temperature, collecting as many minor frames as possible for the available analysis time, usually five to seven per night. XRD data were acquired over multiple nights for the John Klein and Cumberland drill samples to provide acceptable counting statistics. Total data collection times were 33.9 hr for John Klein and 20.2 hr for Cumberland. The data for individual minor frames and for each night's analysis were examined separately, and there was no evidence of any changes in instrumental parameters as a function of time over the duration of these analyses. Before sample delivery and analysis, the empty cell was analyzed to confirm that it was indeed empty before receiving the sample. The flight instrument was calibrated on the ground before flight using a quartz-beryl standard, and measurement of this st...

[1] The Context Camera (CTX) on the Mars Reconnaissance Orbiter (MRO) is a Facility Instrument (i.e., government-furnished equipment operated by a science team not responsible for design and fabrication) designed, built, and operated by Malin Space Science Systems and the MRO Mars Color Imager team (MARCI). CTX will (1) provide context images for data acquired by other MRO instruments, (2) observe features of interest to NASA's Mars Exploration Program (e.g., candidate landing sites), and (3) conduct a scientific investigation, led by the MARCI team, of geologic, geomorphic, and meteorological processes on Mars. CTX consists of a digital electronics assembly; a 350 mm f/3.25 Schmidt-type telescope of catadioptric optical design with a 5.7°field of view, providing a $30-km-wide swath from $290 km altitude; and a 5000-element CCD with a band pass of 500-700 nm and 7 mm pixels, giving $6 m/pixel spatial resolution from MRO's nearly circular, nearly polar mapping orbit. Raw data are transferred to the MRO spacecraft flight computer for processing (e.g., data compression) before transmission to Earth. The ground data system and operations are based on 9 years of Mars Global Surveyor Mars Orbiter Camera on-orbit experience. CTX has been allocated 12% of the total MRO data return, or about !3 terabits for the nominal mission. This data volume would cover $9% of Mars at 6 m/pixel, but overlapping images (for stereo, mosaics, and observation of changes and meteorological events) will reduce this area. CTX acquired its first (instrument checkout) images of Mars on 24 March 2006.

nous of main sequence stars, having masses 0.1-0.5 times the mass of the Sun. The habitable zones around such stars Planets within the habitable zones of M dwarfs are likely to are therefore very close, being typically between 0.03 and be synchronous rotators; in other words, one side is permanently illuminated while the other side is in perpetual darkness. We 0.4 AU [see Fig. 16 of Kasting et al. (1993)]. A planet lying present results of three-dimensional simulations of the atmo-this close to its star will tend to become tidally locked, or spheres of such planets, and comment on their possible habit-in other words be permanently illuminated on one side, ability. Near the ground, a thermally direct longitudinal cell as the threshold for tidal locking after 4.5 byr is r lock Ȃ exists, transporting heat from the dayside to the nightside. The 0.5(M star /M sun ) 1/3 [see Fig. 16 of Kasting et al. (1993) and circulation is three-dimensional, with low-level winds returning Dole (1964)]. Such planets are termed synchronous rotamass to the dayside across the polar regions. Aloft, the zonally tors, and their rotation rates are therefore governed by averaged winds display a pattern of strong superrotation due to the size of their orbits (this is dealt with below). these planets' finite (albeit small) rotation rate. With terrestrialIf the atmosphere of such a planet is in radiativevalues of insolation, a CO 2 /H 2 O atmosphere collapses, or con-convective equilibrium, the surface temperature T 0 on the denses on the surface of the darkside, when surface pressure dayside will be very high, while the nightside will be so is approximately 30 mb, this value being much lower for a N 2 cold that the major atmospheric constituent will condense atmosphere. This temperature contrast is also sensitive to facout on the surface. When this happens, the surface tempertors such as gravity, planetary radius, and IR optical depth .ature of the darkside, as well as the mean surface pressureThese results question the suitability of the concept of a habitp 0 , is set by a balance between upwelling thermal radiation able zone around M dwarfs that is independent of planetary and release of latent heat by condensing constituents, simiparameters. If CO 2 partial pressure is controlled by the carbonlar to the scenario that has been postulated for the martian ate-silicate cycle, we find that these planets should have a atmosphere at those times when a permanent polar cap minimum surface pressure of 1000-1500 mb of CO 2 , as this is forms (see, e.g., Toon et al. 1980). In this latter case, surface the minimum pressure needed to support stable liquid water pressures have been modeled as being as low as 1-3 mb on the darkside at the inner edge of the habitable zone. We finally conclude that planets orbiting M stars can support atmo- (Toon et al. 1980). This phenomenon is termed atmospheric spheres over a large range of conditions and, despite constraints collapse, and has been put forward as the primary reason such as stellar activity, are very likel...

International audienceSamples from the Rocknest aeolian deposit were heated to ~835°C under helium flow and evolved gases analyzed by Curiosity's Sample Analysis at Mars instrument suite. H2O, SO2, CO2, and O2 were the major gases released. Water abundance (1.5 to 3 weight percent) and release temperature suggest that H2O is bound within an amorphous component of the sample. Decomposition of fine-grained Fe or Mg carbonate is the likely source of much of the evolved CO2. Evolved O2 is coincident with the release of Cl, suggesting that oxygen is produced from thermal decomposition of an oxychloride compound. Elevated δD values are consistent with recent atmospheric exchange. Carbon isotopes indicate multiple carbon sources in the fines. Several simple organic compounds were detected, but they are not definitively martian in origin