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| Titel |
Effect of nontronite smectite clay on the chemical evolution of several organic molecules under simulated Mars surface UV radiation conditions |
| VerfasserIn |
Olivier Poch, Tristan Dequaire, Fabien Stalport, Maguy Jaber, Jean-François Lambert, Cyril Szopa, Patrice Coll |
| Konferenz |
EGU General Assembly 2015
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 17 (2015) |
| Datensatznummer |
250109284
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| Publikation (Nr.) |
 EGU/EGU2015-9178.pdf |
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| Zusammenfassung |
| The search for organic carbon-containing molecules at the surface of Mars, as clues of past
habitability or remnants of life, is a major scientific goal for Mars exploration. Several lines
of evidence, including the detection of phyllosilicates, suggest that early Mars offered
favorable conditions for long-term sustaining of water. As a consequence, we can assume that
in those days, endogenous chemical processes, or even primitive life, may have produced
organic matter on Mars. Moreover, exogenous delivery from small bodies or dust
particles is likely to have brought fresh organic molecules to the surface of Mars up
today. Organic matter is therefore expected to be present at the surface/subsurface of
the planet. But the current environmental conditions at the surface - UV radiation,
oxidants and energetic particles - generate physico-chemical processes that may
affect organic molecules. On the other hand, on Earth, phyllosilicates are known to
accumulate and preserve organic matter. But are phyllosilicates efficient at preserving
organic molecules under the current environmental conditions at the surface of
Mars?
We have monitored the qualitative and quantitative evolutions of glycine, urea and
adenine interacting with the Fe3+-smectite clay nontronite, one of the most abundant
phyllosilicates present at the surface of Mars, under simulated Martian surface ultraviolet
light (190-400 nm), mean temperature (218 ± 2 K) and pressure (6 ± 1 mbar) in a laboratory
simulation setup. We have tested organic-rich samples which may be representative of the
evaporation of a warm little pond of liquid water having concentrated organics
on Mars. For each molecule, we have observed how the nontronite influences the
quantum efficiency of its photodecomposition and the nature of its solid evolution
products.
The results reveal a pronounced photoprotective effect of nontronite on the evolution of
glycine and adenine: their efficiencies of photodecomposition are reduced by a factor of 5
when mixed with nontronite at a concentration of 2.6x10-2 mole per gram. Moreover when
the amount of nontronite in the sample of glycine is increased by a factor of two, the gain of
photoprotection is multiplied by a factor of five. This indicates that the photoprotection
provided by the nontronite is not a purely mechanical shielding effect, but is at least partly
due to stabilizing interactions. No new evolution product was firmly identified, but the results
obtained with urea suggest a particular reactivity in the presence of nontronite, leading to an
increase of its dissociation rate, in strong contrast with the other two molecules. |
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