Toulouse, France
Toulouse, France
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Wilson J.T.,Durham University | Wilson J.T.,The Johns Hopkins Applied Physics Laboratory | Eke V.R.,Durham University | Massey R.J.,Durham University | And 4 more authors.
Icarus | Year: 2018

We present a map of the near subsurface hydrogen distribution on Mars, based on epithermal neutron data from the Mars Odyssey Neutron Spectrometer. The map's spatial resolution is approximately improved two-fold via a new form of the pixon image reconstruction technique. We discover hydrogen-rich mineralogy far from the poles, including ∼10 wt.% water equivalent hydrogen (WEH) on the flanks of the Tharsis Montes and >40 wt.% WEH at the Medusae Fossae Formation (MFF). The high WEH abundance at the MFF implies the presence of bulk water ice. This supports the hypothesis of recent periods of high orbital obliquity during which water ice was stable on the surface. We find the young undivided channel system material in southern Elysium Planitia to be distinct from its surroundings and exceptionally dry; there is no evidence of hydration at the location in Elysium Planitia suggested to contain a buried water ice sea. Finally, we find that the sites of recurring slope lineae (RSL) do not correlate with subsurface hydration. This implies that RSL are not fed by large, near-subsurface aquifers, but are instead the result of either small (< 120 km diameter) aquifers, deliquescence of perchlorate and chlorate salts or dry, granular flows. © 2017 Elsevier Inc.

Toplis M.J.,IRAP OMP | Bell J.F.,Arizona State University | Chassefiere E.,University Paris - Sud | Sotin C.,NASA | And 2 more authors.
Space Science Reviews | Year: 2013

The Special Issue of Space Science Review 2013 discusses the ISSI-Europlanet Workshop entitled 'Quantifying the Martian Geochemical Reservoirs', organized in April 2011 at Bern with the objective to create a diverse interdisciplinary forum composed of scientists directly involved in space-based exploration of the Martian surface, meteoriticists studying SNC meteorites, and planetary and/or Earth scientists simulating, numerically or experimentally, the physical and chemical processes occurring on or within Mars. The special volume begins with a paper by Brasser, describing current thoughts on the formation of Mars, the reasons for its relatively small size, the composition of its building blocks and its accretion time-scale. The second contribution by Mezger and co-researchers is largely based on isotopic studies of the SNC meteorites, which can be used to constrain the extent and time-scales of planet-wide differentiation into a core, mantle, and crust. Lasue focuses on the Martian hydrosphere/crusher, considering the morphological evidence for the presence of water, both at the present time and in the past.

Souriau A.,IRAP OMP | Rigo A.,IRAP OMP | Sylvander M.,IRAP OMP | Benahmed S.,IRAP OMP | Grimaud F.,IRAP OMP
Tectonophysics | Year: 2014

The Pyrenees results from the convergence of the Iberian and Eurasian plates since Cenozoic, but the present stress regime of the range is debated, as most of the recent earthquakes exhibit normal solutions. We analyse the seismicity in central-western Pyrenees, which is the most active part of the range with the largest events. Seismicity maps obtained at different depths reveal quasi-periodic features in focus distribution, and a preferential occurrence of large earthquakes at the base of the upper crust. The superimposition of the seismicity to the gravity anomalies shows that earthquakes are mostly located on the southern border of positive Bouguer anomalies, which correspond to dense lower crust blocks trapped in the upper crust during the Pyrenean convergence. We propose that the seismicity results from the subsidence of these blocks previously exhumed inside pull-apart basins. This scenario explains all together the geographic distribution of the seismicity, its magnitude distribution and the predominance of normal focal solutions. It shows that the normal mechanisms do not necessarily imply a general north-south extension of the range, but may be compatible with a weak compressive regime, and that the stress field may not be uniform along the range. © 2014 Elsevier B.V.

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