sábado, 21 de abril de 2012

Features on Mars Erased From Existence

Mars is an ever-changing world: a view from the Mars Reconnaissance Orbiter in 2010 showed tracks from a rolling boulder; in an image of the same region 1 Mars year later the tracks have dissapeared. Credit: NASA/JPL/University of Arizona
More proof that Mars is an ever-changing world: In 2010, the Mars Reconnaissance Orbiter’s HiRISE camera spotted evidence that a boulder had rolled down an incline in a crater. The boulder left a visible track in the Martian regolith big enough to be spotted by MRO. But just one Martian year later, the tracks are gone, erased from existence.
“This is most likely due to the fine bright dust that is transported in the atmosphere falling down and re-covering the dark markings,” wrote Ross A. Beyer on the HiRISE site.
Beyer said the boulder tracks are much darker because as the boulders roll “they set off miniature dust avalanches. The bright, fine dust slides away, leaving a darker, larger grained dust underneath.”
How do boulders start moving on Mars? The boulders were disturbed in some way, breaking them loose from the crater edge, and there are two different possibilities. One, is that a meteorite impact or other tremor shook the boulder loose. Another possibility, as in the case of avalanches MRO has seen on Mars, the spring thawing of frozen carbon dioxide which forms during the Martian winter can cause rocks and debris to break loose from a cliff or incline.
Mars is certainly not the dead world we once thought it was, and the power of HiRISE keeps revealing a changing, unpredicatable landscape.
Source:  Universe Today

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