Francois Poulet

Detection of Hydrated Silicates in Crustal Outcrops in the Northern Plains of Mars

Hydrated Minerals on Martian Northern Plains The presence of hydrated minerals on the surface of Mars implies that the crust of the planet was once altered by the action of liquid water. This conclusion is well established for the ancient southern highlands of Mars, but the situation in the northern lowlands, which are thought to have been resurfaced by lava flows during the Hesperian period about 3 billion years ago, is not so clear. Carter et al. (p. 1682) report the detection of hydrated minerals in nine northern plain craters, which are thought to have exposed the ancient, pre-Hesperian crust. The results suggest that the degree of alteration of the ancient martian crust is more extensive than previously assumed. The extent of the alteration of the crust of Mars by liquid water is greater than previously estimated. The composition of the ancient martian crust is a key ingredient in deciphering the environment and evolution of early Mars. We present an analysis of the composition of large craters in the martian northern plains based on data from spaceborne imaging spectrometers. Nine of the craters have excavated assemblages of phyllosilicates from ancient, Noachian crust buried beneath the plains’ cover. The phyllosilicates are indistinguishable from those exposed in widespread locations in the southern highlands, demonstrating that liquid water once altered both hemispheres of Mars.

History of the clay‐rich unit at Mawrth Vallis, Mars: High‐resolution mapping of a candidate landing site

The Mawrth Vallis region is covered by some of the largest phyllosilicate-rich outcrops on Mars, making it a unique window into the past history of Mars in terms of water alteration, potential habitability, and the search for past life. A landing ellipse had been proposed for the Curiosity rover. This area has been extensively observed by the High Resolution Imaging Science Experiment and the Compact Reconnaissance Imaging Spectrometer for Mars, offering the possibility to produce geologic, structural, and topographic maps at very high resolution. These observations provide an unprecedented detailed context of the rocks at Mawrth Vallis, in terms of deposition, alteration, erosion, and mechanical constraints. Our analyses demonstrate the presence of a variety of alteration environments on the surface and readily accessible to a rover, the presence of flowing water at the surface postdating the formation of the clay-rich units, and evidence for probable circulation of fluids in the rocks at different depths. These rocks undergo continuous erosion, creating fresh outcrops where potential biomarkers may have been preserved. The diversity of aqueous environments over geological time coupled to excellent preservation properties make the area a very strong candidate for future robotic investigation on Mars, like the NASA Mars 2020 mission.

Multi-band processing of observations of the polar regions of Mars with the Omega imaging spectrometer on board Mars Express

The Omega imaging spectrometer on-board the Mars Express ESA mission [1] has observed the surface of Mars during more than 3 Martian years since orbit insertion in January 2004. The spectral cubes (352 spectels from 0.36 µm to 5.1 µm, IFOV from 0.3 to 5 km, swath width 16 pixels to 128 pixels) provide unique information on martian polar processes as there are very strong signatures of CO2 ice and H2O ice in the near IR spectral range. These two ices can be discriminated with multi-band processing, which can also identify the contribution of aerosol scattering when combined with a Monte-Carlo radiation transfer model. This made it possible to investigate the advance and retreat of seasonal caps, the composition of perennial caps and the presence of ices in aerosols. Work in progress with OMEGA focuses on two main issues: inter-annual variability (mainly observed for time-varying phenomena at high latitudes) and modeling of the impact of aerosols on observed spectra so as to retrieve the spectral characteristics of the surface while obtaining information on the composition, grain size and altitude distribution of aerosols. A 3-D model dedicated for observations at very high incidences has recently been developed and will be applied to high latitude observations.