The Matara Crater on Mars Has Amazing Gullies That Look Like a Painting
And at the beginning of this month, it took a photo as it passed over Mars' Matara Crater, capturing some of the many gullies that run through its sand dunes. Unlike Earth gullies, a gully on Mars likely isn't formed by liquid water, instead thought to be caused by "freeze and thaw of carbon dioxide frost" according to NASA.
But we can go more into the science behind it all in just a moment. See the photo below first, taken by the MRO's "High Resolution Imaging Science Experiment" camera, or HiRISE for short:
Lasting impressions of active flows are a widespread feature on Mars. Gullies on Martian sand dunes, like these in Matara Crater, have formed during flows typically seen during seasonal frost. So far, there's no fresh flows this year, but we'll keep watch. https://t.co/lgHTMVJT8Z pic.twitter.com/3pTUzbhvc2— NASA (@NASA) 7 April 2018
While both of the gullies present in the MRO photo have been active in the past, they haven't shown much activity lately. As mentioned earlier, gullies normally become active in the presence of seasonal frost, and frost is visible around the gullies here, but no fresh flows have been created this year so far.
The term "gully" has a rather unique definition on Mars, just because the Earth definition of the word tends to include "formed by water", which isn't the case here. A Martian gully is defined by NASA as any geographical feature with an "alcove at the top, a channel, and an apron of deposited material at the bottom". But their appearance bears a strong resemblance to Earth gullies formed by water erosion, and so the term sticks.
HiRISE is going to continue watching for features like these as the Orbiter continues to circle around the planet for however much time it has left. First launched in 2005, the MRO has since lost control of its gyroscopes, which means it can no longer tell what direction it's pointing toward much of the time. In response, NASA has been teaching the Orbiter how to navigate by reading star charts.
And for now, that workaround is successful. The MRO can still point its cameras down at Mars' surface, and we can still get photos like these.