Morphological and mineralogical analysis of East Candor Chasma in Valles Marineris on Mars

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Martian polar and circum-polar sulfate-bearing deposits: Sublimation tills derived from the North Polar Cap

Previous spectroscopic studies have shown the presence of hydrated minerals in various kinds of sedimentary accumulations covering and encircling the martian North Polar Cap. More specifically, gypsum, a hydrated calcium sulfate, has been detected on Olympia Planum, a restricted part of the Circum-Polar Dune Field. To further constrain the geographical distribution and the process of formation and accumulation of these hydrated minerals, we performed an integrated morphological, structural and compositional analysis of a key area where hydrated minerals were detected and where the main polar landforms are present. By the development of a spectral processing method based on spectral derivation and by the acquisition of laboratory spectra of gypsum–ice mixtures we find that gypsum-bearing sediment is not restricted to the Olympia Planum dunes but is also present in all kinds of superficial sediment covering the surface of the North Polar Cap and the Circum-Polar Dune Field. Spectral signatures consistent with perchlorates are also detected on these deposits. The interpretation of landforms reveals that this gypsum-bearing sediment was released from the ice cap by sublimation. We thus infer that gypsum crystals that are now present in the Circum-Polar Dune Field derive from the interior of the North Polar Cap. Gypsum crystals that were initially trapped in the ice cap have been released by sublimation of the ice and have accumulated in the form of ablation tills at the surface of the ice cap. These gypsum-bearing sublimation tills are reworked by winds and are transported towards the Circum-Polar Dune Field. Comparison with sulfates found in terrestrial glaciers suggests that gypsum crystals in the martian North Polar Cap have formed by weathering of dust particles, either in the atmosphere prior to their deposition during the formation of the ice cap, and/or in the ice cap after their deposition

Characterization of clouds in Titan's tropical atmosphere

Images of Titan's clouds, possible over the past 10 years, indicate primarily discrete convective methane clouds near the south and north poles and an immense stratiform cloud, likely composed of ethane, around the north pole. Here we present spectral images from Cassini's Visual Mapping Infrared Spectrometer that reveal the increasing presence of clouds in Titan's tropical atmosphere. Radiative transfer analyses indicate similarities between summer polar and tropical methane clouds. Like their southern counterparts, tropical clouds consist of particles exceeding 5 μm. They display discrete structures suggestive of convective cumuli. They prevail at a specific latitude band between 8°-20° S, indicative of a circulation origin and the beginning of a circulation turnover. Yet, unlike the high latitude clouds that often reach 45 km altitude, these discrete tropical clouds, so far, remain capped to altitudes below 26 km. Such low convective clouds are consistent with the highly stable atmospheric conditions measured at the Huygens landing site. Their characteristics suggest that Titan's tropical atmosphere has a dry climate unlike the south polar atmosphere, and despite the numerous washes that carve the tropical landscape

Titan’s cloud seasonal activity from winter to spring with Cassini/VIMS

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Episodic aqueous conditions punctuated dominantly aeolian deposition within the layered sulphate-bearing unit, Gale crater (Mars)

International audienceThe stratigraphy preserved within Aeolis Mons (Mount Sharp) in Gale crater (Mars) shows a major transition from mudstone-rich strata (with subordinate sandstones) recording deposition in lacustrine to fluvial settings into a major sulphate-bearing unit (the Layered Sulphate-bearing unit(LSu)) [1, 2]. This transition is interpreted to represent a major environmental change from wetter conditions toward a more arid palaeoclimate on early Mars. A stratigraphic section over this transition constructed along Curiosity’s traverse shows a vertical change from mudstones withinterstratified sandstones of the Glasgow and Mercou members of the Carolyn Shoemaker formation into strata of the Pontours member which have a strong diagenetic overprint, and thence into largescale cross-stratified sandstones of the Mirador formation that are interpreted to be the deposits of large, migrating aeolian dunes. The lower section of the LSu is dominated by stacked, cross-bedded facies with variable diagenetic overprint, that likely records a purely dry aeolian dune environment [3]. However, higher up in the studied section, approximately 80 m above the base of the Mirador formation, there is a transition into a succession still dominated by large-scale cross-beds but with interstratified lenses of a different sandstone facies. The presence of these lenses within large-scale cross bedded rocks is denoted by a transition to the Contigo member of the Mirador formation

Near-infrared spectral mapping of Titan's mountains and channels

We investigate the spectral reflectance properties of channels and mountain ranges on Titan using data from Cassini's Visual and Infrared Mapping Spectrometer (VIMS) obtained during the T9 encounter (26 December 2005). We identify the location of channels and mountains using synthetic aperture radar maps obtained from Cassini's RADAR instrument during the T13 (30 April 2006) flyby. Channels are evident even in VIMS imaging with spatial resolution coarser than the channel size. The channels share spectral characteristics with Titan's dark blue terrain (e.g., the Huygens landing site) that is consistent with an enhancement in water ice content relative to the rest of Titan. We use this fact to measure widths of ∼1 km for the largest channels. Comparison of the data sets shows that in our study area within the equatorial bright spectral unit east of Xanadu, mountains are darker and bluer than surrounding smooth terrain. These results are consistent with the equatorial bright terrain possessing a veneer of material that is thinner in the regions where there are mountains and streambeds that have likely undergone more recent and extensive erosion. We suggest a model for the geographic relationship of the dark blue, dark brown, and equatorial bright spectral units based on our findings

Nearinfrared spectral mapping of Titan's mountains and channels

Cassini studies of the surface of Titan are beginning to reveal its nature. In addition to hills, channels, and cobbles seen by the Huygens probe, the Visual and Infrared Mapping Spectrometer (VIMS) and RADAR instruments onboard the orbiter have seen sand dunes , channels , mountains [5, 6], and cryovolcanic candidates. Recently the RADAR team announced the discovery of possible lakes near Titan’s north pole