Noachian and more recent phyllosilicates in impact craters on Mars.
Hundreds of impact craters on Mars contain diverse phyllosilicates, interpreted as excavation products of preexisting subsurface deposits following impact and crater formation. This has been used to argue that the conditions conducive to phyllosilicate synthesis, which require the presence of abundant and long-lasting liquid water, were only met early in the history of the planet, during the Noachian period (> 3.6 Gy ago), and that aqueous environments were widespread then. Here we test this hypothesis by examining the excavation process of hydrated minerals by impact events on Mars and analyzing the stability of phyllosilicates against the impact-induced thermal shock. To do so, we first compare the infrared spectra of thermally altered phyllosilicates with those of hydrated minerals known to occur in craters on Mars and then analyze the postshock temperatures reached during impact crater excavation. Our results show that phyllosilicates can resist the postshock temperatures almost everywhere in the crater, except under particular conditions in a central area in and near the point of impact. We conclude that most phyllosilicates detected inside impact craters on Mars are consistent with excavated preexisting sediments, supporting the hypothesis of a primeval and long-lasting global aqueous environment. When our analyses are applied to specific impact craters on Mars, we are able to identify both pre- and postimpact phyllosilicates, therefore extending the time of local phyllosilicate synthesis to post-Noachian times.
Fairén
Alberto G
AG
Carl Sagan Center for the Study of Life in the Universe, 515 North Whisman Road, Mountain View, CA 94043, USA.alberto.g.fairen@nasa.gov
Chevrier
Vincent
V
Abramov
Oleg
O
Marzo
Giuseppe A
GA
Gavin
Patricia
P
Davila
Alfonso F
AF
Tornabene
Livio L
LL
Bishop
Janice L
JL
Roush
Ted L
TL
Gross
Christoph
C
Kneissl
Thomas
T
Uceda
Esther R
ER
Dohm
James M
JM
Schulze-Makuch
Dirk
D
Rodríguez
J Alexis P
JA
Amils
Ricardo
R
McKay
Christopher P
CP
D000538:Aluminum Silicates / Q000032:analysis / Q000737:chemistry; D017632:Asbestos, Serpentine / Q000032:analysis / Q000737:chemistry; D002712:Chlorides / Q000032:analysis / Q000737:chemistry; D005118:Extraterrestrial Environment / Q000737:chemistry*; D005290:Ferric Compounds / Q000032:analysis / Q000737:chemistry; D006358:Hot Temperature; D007616:Kaolin / Q000032:analysis / Q000737:chemistry; D018535:Mars; D008903:Minerals / Q000032:analysis / Q000737:chemistry; D017640:Silicates / Q000032:analysis* / Q000737:chemistry; D013057:Spectrum Analysis / Q000379:methods; D013997:Time Factors
D000538:Aluminum Silicates; D017632:Asbestos, Serpentine; D002712:Chlorides; D005290:Ferric Compounds; D008903:Minerals; D017640:Silicates; C510100:prehnite; D007616:Kaolin; C001599:chlorite