Eridania Basin: An ancient paleolake floor as the next landing site for the Mars 2020 rover

International audienceThe search for traces of past Martian life is directly connected to ancient paleolakes, where ponding water or low-energy water fluxes were present for long time intervals. The Eridania paleolakes system, located along the 180° meridian, is one of the largest lacustrine environments that were once present on Mars. Morphological features suggest that it was constituted by connected depressions filled by water to maximum depths of ∼2400 m and a volume of at least 562,000 km3. We focused our attention on the northern side of the Eridania Basin, where high-albedo, uneven patches of material characterized by the absence of dust are present. Based on OMEGA and CRISM orbital imaging spectroscopy data, a large clay-bearing unit has been identified there. In particular, a set of aqueous minerals in present in the stratigraphy, being visible through erosional windows in the first several tens of meters of the sedimentary sequence. Below this capping unit, a thin Al-rich clay stratum attributable to Al-smectite and/or kaolins is present. This overlies a Fe-rich clay stratum, attributable to the nontronite smectite. At the base of the mineralogic sequence a stratum that could be either a zeolite or more likely a hydrated sulfate is present. In addition, small deposits of alunite (a rare phase on Mars), and jarosite are here found at several locations. Such stratigraphy is interpreted as originating from a surface weathering process similar to terrestrial abiotic pedogenesis; nonetheless, possible exobiologic processes can be also invoked to explain it. NASA's Spirit rover landed on Gusev crater in 2004, near the mouth of the Ma'adim Vallis, which connects this crater with the considered paleolakes system. The Eridania site provides the unique opportunity to complete the measurements obtained in Gusev crater, while investigating the exposed mineralogical sequence in its depositionary setting. In addition, the extremely favorable landing parameters, such as elevation, slope, roughness, rock distribution, thermal inertia and dust coverage, support this location as a possible landing site for the NASA Mars 2020 rover

Is Far-Red Light Photoacclimation (FaRLiP) activated in cyanobacteria exposed to M-dwarf starlight simulated spectra?

Rocky terrestrial exoplanets in the Habitable Zone of M-dwarf stars are ideal to potentially harbour life. However, such stars have different spectral characteristics respect to stars like our Sun, with almost no visible light available and major components in the far-red and infrared. This doesn\u2019t seem suitable for oxygenic photosynthetic organisms, that evolved on Earth to absorb only VIS light. Thanks to the newly developed Star Light Simulator, an instrument able to simulate the emission spectra of different kinds of stars (Sun and M-dwarfs included), we were able to perform growth and photosynthetic analyses on a few species of cyanobacteria irradiated with M-dwarf simulated lights. We selected two strains of cyanobacteria, Chlorogloeopsis fritschii PCC6912 and Synechocystis sp. PCC6803. The first can perform the so-called Far-Red Light Photoacclimation (FaRLiP), that allows it to survive and evolve oxygen in environments rich in far-red lights, thanks to the production of peculiar chlorophylls (chl d and f) and far-red absorbing forms of phycobiliproteins. This makes it a perfect candidate to test the possibility of oxygenic photosynthesis in exoplanets irradiated by M-dwarf spectra. The second cyanobacterium is a model organism for photosynthetic research and was used as a control unable to perform such acclimation. We compared the growth and photosynthetic performances of the cyanobacteria exposed to the M-dwarf simulated light spectra. The results were compared with those obtained from the cyanobacteria exposed to a solar simulated light and a far-red light (730 nm LED). The possibility of oxygenic photosynthesis in exoplanets orbiting the habitable zone of M-dwarfs as well as the activation of the FaRLiP response under these simulated spectra is discussed