Mars Society Switzerland
Gale Crater DustGeology & Atmosphere
Location of Mawrth Vallis, Mars Science Laboratory potential site of landing, at the hedge of the southern higlands and the northern lowlands. The three other potential sites are equally shown on this map. (Image credit : NASA)
In blue, the area where the Institut d’Astrophysique Spatiale de l’Université Paris Sud's OMEGA instrument, embarked aboard the european orbiter Mars Express, identified phyllosilicates (clays), sign of past water abundance. We can see that they do not show within the river bed. (Image credit: ESA/OMEGA/HRSC)
After choosing the landing sites simply on the basis of geographical criteria, should not we try something else (even if the oldest terrains, more cratered are more difficult to access)? If we make a wrong choice, the consequences will be severe because unfortunately Mars missions on the ground are rare, at best one every two and a half years, and because significant discoveries are crucial to encourage the politics to keep funding the exploration. Personally, I am more convinced by the mineralogical logic than by geography and I vote for Mawrth Vallis (but I am not the one who decides!).
The landing ellipse of Mars Science Laboratory (to the extent that this site would be chosen) on the plateau above Mawrth Vallis. (Image Credit : NASA)
On to Mawrth Vallis! The Martian session of the 8th Swiss Geosciences Meeting (“8SGM ") held at the University of Fribourg, Pérolles2, during all the day of November 20th, at the initiative of the Mars Society Switzerland and upon the invitation of the Centre for Hydrogeology and Geothermics of the University of Neuchâtel and the Department of Geosciences of the University of Fribourg, was an opportunity for Swiss and foreign experts to take stock of our geological knowledge of the Red Planet and of the means and objectives of Mars exploration. This cannot be considered of being of trivial interest, as Mars, during its first four or five hundred million years, probably experienced a geologic history quite similar to Earth’s and could therefore accommodate the beginnings of life. Since, from then, almost all the atmosphere escaped into space and erosion virtually stopped, we may nowadays, by observing Mars, consult the first pages of the book of our own history which have been erased on Earth by plate tectonics and erosion. To describe the role of water in the history of Mars (and thus determine the most likely places which could have hosted the emergence of life), the proponents of two opposite theories argued against each other during the congress: On the one hand, Charles Frankel, a member of the Board of Association Planete Mars and a graduate geologist from the University of Arizona, thinks, based on the geographic features and morphological evidences of the planet, that liquid water remained stable for a long time beyond the first geological era, in the lowlands of the northern hemisphere (Vastitas Borealis, the bottom of which extends over large plains smooth and flat at altitudes ranging from 3000 to 6000 meters below the medium level of the planet). He thinks that, for long periods of time, the water has flowed in the dry beds of rivers and been discharged in the lowlands by the estuaries that lead there. He points out that these rivers have a lot more ramifications of tributaries than previously estimated (based on more accurate observations done recently). After the atmosphere was rarefied, the water would have eventually been protected from sublimation by ice surface. He thinks he can see the presence of shorelines (although this remains uncertain) and that the surface of the Northern Plains bears morphologic similarities with the bottom of our oceans. On the other hand, Professor Jean-Pierre Bibring, head of the Institut d'Astrophysique Spatiale of Université Paris Sud and in charge of the OMEGA spectrometer (embarked on board ESA’s satellite MarsExpress) which mapped the mineralogy of March, observed that minerals resulting from a long immersion in water (phyllosilicates, carbonates) under a thick atmosphere of carbon dioxide, are found almost exclusively in ancient cratered terrains, in the South of the planet. Surface rocks in the North (in the "putative" ocean seen by Charles Frankel) are only magmatic. In this area, hydrated metamorphosed rocks (observable in the peak of the Leighton crater, for instance) appear only under the volcanic layer. According to Jean-Pierre Bibring the "Ocean" would only be a lunar type "sea", completely dry, created at the end of Mars wet period (c. -4 billion years) by a giant impactor during the Late Heavy Bombardment caused by the readjustment of orbits of Neptune and Uranus. It is this shock that would have created the crustal dichotomy observed today. The planet's internal dynamo having stopped because of the cooling and stiffening of its mantle, the magnetosphere would have disappeared, the atmosphere would have been blown away by the solar wind and would have never been dense enough again (despite periods of heavy volcanic activity) to allow water to remain liquid on surface for a long time. The river beds and estuaries visible today, would only be traces of cataclysmic floods of water that would have quickly sublimed and never formed stable seas. Moreover, the nature of the hydrated rocks (particularly magnesium phyllosilicates) corresponds to primordial igneous rocks (rich in magnesium and iron) unprocessed by further active geologic phenomena. Jean-Pierre Bibring rejects the "geographic" explanation because the surfaces of the wet period must have been completely chopped and disfigured by the subsequent geological history of Mars. The Late Heavy Bombardment, following the primordial meteorite bombardment and the volcanic episode of the Hesperian epoch would have in fact completely disrupted the planet's surface, without necessarily changing the mineralogy of the rocks. These differences, which also exist among scientists who advise NASA and ESA, will have a direct impact on the choice of the landing site for the upcoming NASA's Mars Science Laboratory (MSL) rover mission to be launched at the end of 2011. For the time being four sites are in competition, all of them in the northern hemisphere, because MSL is scheduled to land, unfortunately, during Mars austral winter. In case the landing ellipse would be somewhere in the southern hemisphere (where hydrated rocks are abundant), the success of the mission risks to be hampered by the cold (even though light would not be such a problem since the vehicle will be nuclear powered). Among the pre-qualified sites, all are located in estuaries but only one in an environment where ancient rocks, Phyllocian type, have been identified by OMEGA and would be accessible. This site is the mouth of Mawrth Vallis (Welsh name of the Mars planet), a river that empties into Chrise Planitia (part of the Northern Great Plains) in the Arabia Terra area (22°4N).
Page 3 Page 2Account of the Mars Session at the 8th Swiss Geoscience Meeting
Methane Atmosphere Frozen CO2 Oceanus Borealis Curiosity 1 Pressures Changes