Interesting snippets from a NY Times article on Rosetta.
http://www.nytimes.com/2015/01/23/s...-a-comet-even-with-a-wayward-lander.html?_r=0
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A close-up of the "neck region" of the rubber-duck-shaped comet. Credit Eureopean Space Agency
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The high-resolution camera has taken photographs with a resolution as fine as two and a half feet per pixel. The comet, just two and a half miles wide with a two-lobe shape that resembles a rubber duck toy, has a remarkably wide variety of terrain. That includes smooth dust-covered regions, fields of boulders, steep cliffs and large depressions that may have been blown out by underground melting of carbon dioxide. The variety is surprising because many think the comet is, by and large, made of the same material throughout. Scientists are not sure if the shape comes from two smaller comets that bumped and stuck together or one large comet that eroded in an unusual manner.
On the surface of Comet 67P, there are even what look like ripples of sand dunes like those seen on
Earth and Mars. That appears befuddling, as a comet has no atmosphere — and so no wind — and only a wisp of gravity.
“You have to ask yourself, is that possible?” said Nicolas Thomas, a professor of experimental physics at the University of Bern in Switzerland and lead author of one of the papers. Dr. Thomas said that back-of-the-envelope calculations indicated that it might be plausible, with the jets of gas acting as wind and the particles held together through intermolecular attraction known as the van der Waals force instead of gravity. “You can convince yourself you can make them move,” Dr. Thomas said. “It’s plausible, at least at the moment.”
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A large fracture running across the comet. Credit Eureopean Space Agency
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In another region, along the comet’s “neck,” is a cliff about 3,000 feet high with fractures hundreds of feet long. The scientists cannot agree on what they are seeing, whether the lines reflect layering in the material making up the comet or cracks caused by the heating and cooling of the material as it passes in and out of sunshine.
In the smooth regions, there are circular structures. “Which look very, very bizarre,” Dr. Thomas said. “To be frank, we don’t know how those things were created. We have no clue.”
