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| Titel |
DAN measures water in the soil of the Gale crater: new results from Curiosity |
| VerfasserIn |
Igor Mitrofanov, Maxim Litvak, Anton Sanin, Richard Starr, Denis Lisov, Ruslan Kuzmin, Alberto Behar, William Boynton, Craig Hardgrove, Karl Harshman, Ionsoo Jun, Ralf Miliken, Michael Mischna, Jeffrey Moersch, Criss Tate |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250091388
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| Publikation (Nr.) |
 EGU/EGU2014-5679.pdf |
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| Zusammenfassung |
| The Gale crater was selected as the landing site for NASA’s rover Curiosity (1). Since the
landing in the August 2012, the neutron active instrument DAN (2) is performing active
testing measurements of ground water and chlorine content along the traverse of the rover.
The best model for the water content in the subsurface was found to be the 2-layer one, with
the traverse-averaged contents of water in the top and bottom layers 1.51±0.42 wt% and
2.97±1.16 wt%, respectively. The traverse-average thickness of the top layer is about
18.5±8.0 cm, and the traverse-average content of chlorine is about 1.14±0.25 wt%. The
uncertainties of the values above represent the physical dispersion of measurements along the
traverse, while the uncertainties of individual measurements are much smaller for each tested
spot.
These values are not consistent with the predictions for the ground water and chlorine in
the Gale, which were based on the orbital measurements by GRS suite onboard Mars
Odyssey (3). The average content of water around Gale, provided it is depth independent, was
found to be about 5 wt%. More accurate estimations based on 2-layer model provide even
much more water in the subsurface. The content of chlorine was determined from the orbit,
about 0.5 wt%. The difference between water content estimations based on the orbital and
surface data are larger than the statistical uncertainty, and one cannot explain the
difference by different depth of neutron sensing by DAN and GRS. Therefore, one
should consider the physical reason for depletion of ground water and enhancement
of chlorine in Gale in comparison with the content in the soil of the surrounding
area.
The Gale was not the natural site of soil hydratation, the soil around the crater has the
water at higher content. During the epoch of wet Mars, the transport of soil by creeks and
rivers into the Gale lake was probably associated with some selection process, which
predominantly supply particles with larger sizes and less content of chemically bound water.
Also, the wind erosion of Gale during the layer dry epochs was probably also associated with
some size-selection process, when lighter particles were predominantly removed. As the
result, a soil with less chemically bound water has been deposited in the Gale sediments, and
more water has evaporated to the atmosphere from this soil. Such simple consideration could
be suggested for explaining, why the soil at the Gale floor contains less water and more
chlorine, than the area around the crater, as it is requested by the surface and orbital
observations.
References
(1) Grotzinger J.P., J. Crisp, A. R. Vasavada, R. C. Anderson, C. J. Baker, et al. (2012),
Space Sci. Rev., 170, p. 5-56.
(2) I.G. Mitrofanov et al. (2012), Space Science Rev. Vol. 170, issues 1 – 4, pp.
559-582.
(3) W.Boynton et al. (2007), Journal of Geophysical Research, Volume 112, Issue E12. |
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