Dans la partie est des canyons, la présence simultannée
de ces absorptions minérales et de très fortes signatures
de minéraux hydratés suggère une formation hydrovolcanique (Murchie et al., Icarus 2000).
Ces caractéristiques spectrales renforcent fortement l'hypothèse
d'une mise en place par éruptions sous des plans d'eau stables ou
métastables, probablement des lacs à surface gelée.
C'est donc une indication (indirecte) de la présence d'eau liquide
sur Mars à une période relativement récente.
Pyroxenes themselves are grouped
in two families, and have another band located between 1.8 and 2.2 µm.
The location of this second band and the intensity ratio between the two
bands are reliable mineralogical parameters. In the areas observed, this
band is always located around 2.2 µm and indicates higher abundance
in high-calcium pyroxenes. Detailed spectral modeling (Mustard et al., Icarus 1997) shows that the darkest regions are actually two-pyroxene mixtures with high- and low-calcium components;
such a composition is very similar to that of the basaltic SNC meteorites,
that are believed to originate from Mars. This composition results from
magma formation, and therefore permits to understand the physical and chemical
conditions existing during formation.
In the eastern part of the canyon, the presence of strong pyroxene absorptions
together with deep hydration bands suggests hydrovolcanism (Murchie et al., Icarus 2000). These spectral
properties strongly reinforce the hypothesis of a formation by volcanic
processes taking place under stable or metastable still water, possibly
frozen lakes. Hence, this is a strong, but indirect, evidence for the presence
of liquid water on Mars in a relatively recent past.
ISM
a été développé avec le soutien du CNES
Dernière mise à jour : 11 mai 2001
Adresse : http://www.ias.u-psud.fr/ism/