Astronomy and Astrophysics – Astronomy
Scientific paper
Oct 2007
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2007dps....39.1407h&link_type=abstract
American Astronomical Society, DPS meeting #39, #14.07; Bulletin of the American Astronomical Society, Vol. 39, p.436
Astronomy and Astrophysics
Astronomy
1
Scientific paper
In December 2006, Malin et al. (Science) reported discovery of small Martian craters forming on Mars in the last 7 years. Diameters are 10 to 20 m for best detections. The formation rate for these craters is within a factor 2-3 of the rates I've used in the isochron system I developed at PSI (2005 Icarus) - which is within the uncertainty limits of factor 2-4 that I have quoted for the system. This supports the conclusion that order-of-magnitude ages can be measured for young, kilometer-scale Martian landforms, by counting small craters. If Malin et al. are right, the method can be refined to considerable precision in the future, by better measurement of small crater production rates.
I have applied this dating system to tongue-shaped flows and debris aprons east of Hellas. These apparently involve flow of ice or ice/soil mixtures (Costard et al. 2002 Science). Surface features at lateral topographic scales of 10-20m and 3-6m depth consistently give ages of a few My to a few 10s My on the flow units, and older ages outside the flow units. This is true whether Hartmann, Malin, or Neukum cratering data are used. These ages are just in the range of the last few cycles of high obliquity (Laskar et al. 2002 Nature). Strikingly, the ice features are exactly in one of the two moderate-latitude regions with unusually high ice deposition at high obliquity, according to global climate models by Forget (2007 LPSC, private communication).
I conclude that crater count chronometry is viable and we have evidence of localized high rates of ice deposition, and possible water release, on mid-latitude Mars within the last few tens of My.
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