Credit: HiRISE, MRO, LPL (U. Arizona), NASA
What are these weird streaks on Mars? Anyone’s guess. They’re neat-looking, at any rate!
What creates these picturesque dark streaks on Mars? No one knows for sure. A leading hypothesis is that streaks like these are caused by fine grained sand sliding down the banks of troughs and craters. Pictured above, dark sand appears to have flowed hundreds of meters down the slopes of Acheron Fossae. The sand appears to flow like a liquid around boulders, and, for some reason, lightens significantly over time. This sand flow process is one of several which can rapidly change the surface of Mars, with other processes including dust devils, dust storms, and the freezing and melting of areas of ice. The above image was taken by the HiRise camera on board the Mars Reconnaissance Orbiter which has been orbiting Mars since 2006. Acheron Fossae is a 700 kilometer long trough in the Diacria quadrangle of Mars.
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My name is Danielle Signor, and I am a space cadet. 
#1 by John Soares on March 6, 2010 - 3:44 pm
Seems to happen on quite shallow slopes. The sand must have very low viscosity.
I wonder if some chemical weathering altered the color of the flow material, and what could have caused it.
#2 by Danielle on March 12, 2010 - 2:40 pm
It’s possible (chemical weathering), because the surface dust is definitely a different color than the dark underlying material. It seems like each week they find something new and strange about Mars. I hope I see some geologists on the surface in my lifetime!
#3 by russ on March 12, 2010 - 2:30 pm
I saw this on APOD and was mesmorized. We need to walk there. A human can do in 20 minutes what it took Spirit or Opportunity months or years to do.
#4 by Danielle on March 12, 2010 - 2:37 pm
No doubt. Spoken like a true geologist!