Alien Textures 'Weird Stuff'
Summary (Jan 07, 2004): Judging from just the glimpses of high-resolution imagery coming from Mars, some bizarre features of the Spirit rover's immediate neighborhood has geologists scratching their heads. The instrument package, called Athena, will be very capable of getting good answers once it rolls off its landing petal in a week or so. Until then, geologists are hard-pressed to find a good terrestrial analog to some kinds of folded patches.
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Alien Textures 'Weird Stuff'
Geologists Just Scratching the Surface
Nearby where the Spirit rover is now surveying, one of the most unusual formations has geologists scratching their heads for a good terrestrial analogy.
"The soil was stripped up and folded in an interesting way," said Jim Bell, who designed the panoramic camera that Spirit used to photograph the "mud-like" patch. "It has quite alien textures."
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A section of the large color panorama from the Mars Spirit pancam, showing the alien textures. Middle foreground shows what may be surface abrasion from retracting airbags, but the larger 'mud-like' or cemented surface has an unusual texture that geologists are intrigued about sampling. Large image [2 Mb]
Credit: NASA/JPL/Cornell |
"It is bizarre," said Steve Squyres, principal investigator on the NASA team. "It's strangely cohesive. It's not like anything I've ever seen before. It's weird stuff."
Squyres said the patch looked similar to but not exactly like what had been termed "duricrust" at the landing site of the 1976 Viking probe.
"One suggestion for these has been that moisture was getting through the soil and evaporating and leaving behind some salts that help cement the soil together," he said. "Our instruments will be very good at measuring that."
Duricrust involves places where the dust is cemented locally to about a few millimeters to a few centimeters' depth. For most examples, duricrusts are speculated to be caused by water that sublimates from ice that's relatively deeper below the surface and then migrates toward the surface. It condenses very briefly at the surface, melting cementum -- that is clay-like material -- and very loosely binding the Martian sand together.
Martian sand grains are maybe on the order of tens to hundredths of microns in size--much more like flour than sand, with sizes much smaller than the width of a human hair.
The abrasion imaged in the forecground is thought to be part of the trail from an airbag retracting and scratching the surface. But the mud-like patch in the upper right is what is considered a more exotic geological surface.
Matt Golombek, chief scientist for the 1997 Pathfinder mission, told
Astrobiology Magazine about his initial impressions from the panoramas: "We didn't see any dunes, really, just a few small ones, like [at the] Pathfinder [site]. We saw what looks like a lag deposit, like you've taken away all the fines and what you're left with are the rocks that are too big [for
the wind] to move. And a duricrust surface, which is a more heavily cemented surface, particularly in the center of a bowl-shaped crater [visible in some images]".
Terrestrially in snowy areas, this kind of duricrust is closest in texture to the crust that forms on those extremely cold winter days when the powdery snow was underneath but there's a crust on top. If you're light enough, you can even walk on that crust, as it will support your weight. The Martian duricrust is not thought to be that thick or strong, but the particular cemented area in some parts of the panorama has scientists intrigued about testing its real texture, composition and strength.
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Earth and Mars
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Wednesday, January 07, 2004
