Back At Larry's Lookout |
Back At Larry's Lookout |
Guest_Sunspot_* |
May 18 2005, 06:29 PM
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#1
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Guests |
Some pretty complex driving by the look of it:
http://qt.exploratorium.edu/mars/spirit/fo...E0P1214R0M1.JPG Now this is odd: http://qt.exploratorium.edu/mars/spirit/na...E0P0617R0M1.JPG It looks like some of the rocks have slid down the dune |
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Jun 7 2005, 07:49 AM
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#2
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Senior Member Group: Members Posts: 1870 Joined: 20-February 05 Member No.: 174 |
On Earth, sediment transport processes tend to separate sand sized (1 to 0.1 mm, roughly) sized particles from smaller silt and clay sized particles. (Geologist's operational test to tell siltstone from claystone: nibble a bit between your front teeth. If it's gritty, it's got silt sized particles, if it's smooth, it's all clay sized!) Thus Earth gets lots of relatively well sorted sandstones, and very different silt dominated sediments on land and in rivers. Clay sized dust tends to stay in suspension in the air or rivers and ends up in the oceans as a component of marine oozes.
On Mars, the globally transported dust storm dusts are mostly clay sized... a few microns sized particles, and the dark dunes in craters and the north polar sand seas do appear both visually and from thermal properties to be reasonably well sorted sand grains, but a lot of the stuff the rovers are encountering seem to be a varied assortment of clay/silt/sand and granule (2 mm or so) sized materials, with all sorts of small scale sorting going on, but not making sediments with really well defined average particle sizes. A big reason is the lack of water and it's roles in separating the different materials mechanically, and the lack of oceans to trap the eolian transported dust. A big question polar lander was to help answer and Phoenix will tackle is the nature of high latitude "dust and ice" deposits. The Polar Lander's targets are true polar deposits, it's unclear what the dirty ice (inferred from Odyssey's data) are that Phoenix is targeted for. |
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