Noachian and more recent phyllosilicates in impact craters on Mars

Our plain-English summary of Noachian and more recent phyllosilicates in impact craters on Mars, by A.G. Fairén, V. Chevrier, O. Abramov, et al (Proceedings of the National Academy of Sciences of the United States of America, 2010).

The study

• Authors: A.G. Fairén, V. Chevrier, O. Abramov, G.A. Marzo, P. Gavin, A.F. Davila, L.L. Tornabene, J.L. Bishop, T.L. Roush, C. Gross, T. Kneissl, E.R. Uceda, J.M. Dohm, D. Schulze-Makuch, J.A. Rodríguez, R. Amils, C.P. McKay
• Journal: Proceedings of the National Academy of Sciences of the United States of America
• Published: 2010;107(27):12095-100
• Cited by: 11 articles, as counted by NIH iCite
• Read it: PubMed · Publisher · Free full text

Abstract

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.

In plain English

This was a planetary geology study of clay-type minerals called phyllosilicates in impact craters on Mars. It did not study asbestos, workers or human health. The authors heated laboratory samples of nontronite, montmorillonite, chlorite, kaolinite, prehnite and serpentine and measured their infrared spectra. Above 600 °C the minerals became unstable, and above 800 °C all of them were altered into amorphous silica glasses. The authors then calculated temperatures inside craters during impacts. These exceeded the minerals' stability limits only in a central area around the point of impact, which could cover up to 30% of the crater radius for craters larger than 100 km. In Toro crater, which is 42 km across, the modelled minimum temperature in the central uplift was near 650 to 800 °C. Prehnite appeared on the southern central peak but not on a northern peak with intact older rock layers. The authors concluded that most crater phyllosilicates are consistent with excavated older deposits, while some at Toro formed by impact-triggered hydrothermal activity after the Noachian period.

We wrote this plain-English summary from the full article with the help of AI, and a second AI model checked each sentence against the article. It is not the authors' wording; the abstract and the article are their own account.

What the study did and found

• Design: Laboratory heating experiments on mineral samples, combined with computer modelling of impact temperatures and analysis of orbital remote-sensing images (case study of one Martian crater)
• Who was studied: Not people. Laboratory samples of six phyllosilicates (nontronite, montmorillonite, chlorite, kaolinite, prehnite, serpentine), modelled Mars impacts, and Toro crater on Mars (42 km diameter, 2 km deep)
• Exposure: No asbestos or human exposure was studied. The 'exposure' was heat: 1-g mineral samples were heated to about 300 to 1100 °C for 4 to 24 hours, in air and under carbon dioxide
• Main results:
  • In the laboratory, phyllosilicates heated above 600 °C became unstable, with phase transformation and loss of volatile components
  • Above 800 °C, all phyllosilicates studied were altered into amorphous silica glasses
  • Modelled impact temperatures exceeded the minerals' stability limits only in a central area around the point of impact, which could cover up to 30% of the crater radius for craters over 100 km in diameter
  • For Toro crater, the preexisting materials now forming the central uplift reached a modelled minimum temperature near 650 to 800 °C
  • Prehnite was associated with Toro's southern central peak, but was absent from the northern peak, which contains intact preexisting rock layers. The authors read this as prehnite not having been part of the preimpact sediments
• The authors' conclusion: The authors concluded that phyllosilicates in crater floors, walls, rims and ejecta are consistent with excavated preexisting deposits. They also concluded that some phyllosilicates at Toro crater formed by impact-triggered hydrothermal activity after the Noachian period
• Limitations the authors state:
  • The model used vertical (90 degree) impacts to estimate maximum temperatures. The authors note that oblique impacts would give lower temperatures
  • The authors state that identifying minerals formed after the impact is far more difficult than identifying preexisting ones, and that high-resolution data are needed
  • The authors note that phyllosilicates in crater central areas can also be preexisting sediments, and that access to Martian craters is limited

Topics

The National Library of Medicine indexes this study under subjects our site covers: Chrysotile.

Medical terms in this study, explained in our Lexicon: Phyllosilicates.

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