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New perspectives of research and change of strategy in the search for life on Mars

Wednesday, January 29, 2014

Mars has always been viewed as a planet similar to Earth, with rivers of water and even rift zones, but MRO data revealed that things are quite different than we thought before. The recent discovery of several alignments of volcanoes on the southern hemisphere of Mars (Leone, 2014a) raises the question about their origin. The main hypothesis is that the alignments might be due to the migration of mantle plumes subsequent to a giant impact with a lunar sized body at the South Pole of the planet. Neither analogous presence nor alignments of volcanoes are observed in the northern lowlands thus making quite problematic the Northern Giant Impact hypothesis. Previous works have also proposed the rotation of the whole Martian lithosphere to explain the migration of a mantle plume to Tharsis but the observation of several new volcanic alignments is better explained by the Southern Giant Impact hypothesis for the formation of the dichotomy because this model produces several migrating mantle plumes from the Equator to the South Pole and thus provides an important link between a catastrophic event early in the history of Mars and the emplacement of a peculiar volcanism not observed elsewhere in the Solar System. The role of lava tube networks and lava channels was reassessed as the primordial stage of the volcano-erosional processes that formed the Labyrinthus Noctis-Valles Marineris system and showed to be more plausible than a tectonic origin in the stagnant lid of Mars (Leone, 2014b). The combined use of CTX, CRISM, HiRISE imagery, and MOLA profiles has provided valuable insight in the evolution of pit chains into fossae first and chasmata later due to mass wasting processes caused by the erosional effect of the lava flows that draped Valles Marineris and other outflow channels. The images of ubiquitous lava flows rather than scattered light-toned deposits strengthen the role of lava over that of water in the erosional processes that formed Labyrinthus Noctis and carved Valles Marineris deeper than any other outflow channel on Mars, a comparison between outflow channels on Elysium and Tharsis suggests that the availability of lava supply is correlated to their widths. Even Chryse Planitia appears to be mantled by thick lava flows. These findings, coupled with the lack of evidence for life (sedimentary layers on Earth are often packed with shells and fossils that have never been found on Mars) in places supposed to be filled with water but that revealed lava instead (i.e. Chryse Planitia), open new horizons of research and suggest that a change of strategy is required in the search for life on Mars. Many traces in Valles Marineris indicate that water followed volcanism (Weitz et al., 2010; Leone, 2014b) and reassessing water amounts can help to track and constrain the places where it could have been stored enough to form a life friendly environment. The surface of Mars does not seem today so friendly for (liquid) water and life, thus it would be much better to look for accessible pathways to the underground. Volcanic areas show pathways to old lava tubes and hydrothermal environments likely to provide a safer shelter than the surface to eventual lifeforms once active volcanism ended. Furthermore, the controversial presence and temporal variations of a biomarker gas like methane, if confirmed, shows an intriguing association with several volcanic areas of Mars. Exploring existing skylights with rovers like Curiosity, equipped to detect gases and to delivery probes underground, can help to understand if these really are the areas of venting for methane and, in positive case, to provide some clues to its origin.

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