A mysterious gully has been spotted on Mars that wasn't there in 2010, according to NASA images. What caused the gully?
Wired has more:
A new gully has appeared on a sloped crater wall on Mars. The channel, which was absent from images in November 2010 but showed up in a May 2013 photo, does not appear to have been formed by water. Exactly what caused this Red Planet rivulet remains a mystery.
The winding gully seems to have poured out from an existing ribbon channel in a crater in Mars’ Terra Sirenum region. The leading hypothesis on how the gully formed is that debris flowed downslope from an alcove and eroded a new channel. Though it looks water-carved, the gully is much more likely to have been formed when carbon dioxide frost accumulated on the slope and grew heavy enough to avalanche down and drag material down with it.
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