How wind created mile-high mounds on Mars

Wind carved massive mounds of more than a mile high on Mars over billions of years, say researchers, suggesting that their location can help pin down when water on the Red Planet dried up during a global climate change event.

"The findings show the importance of wind in shaping the Martian landscape, a force that, on Earth, is overpowered by other processes," said lead author Mackenzie Day from the University of Texas at Austin.

"On Mars, there are no plate-tectonics and no liquid water so you don't have anything to overprint that signature and over billions of years you get these mounds, which speaks to how much geomorphic change you can really instigate with just wind," Day informed.

Wind could never do this on Earth because water acts so much faster, and tectonics act so much faster.

First spotted during NASA's Viking programme in the 1970s, the mounds are at the bottom of craters.

Recent analysis by the Mars rover Curiosity of Mount Sharp has revealed that the thickest ones are made of sedimentary rock, with bottoms made of sediments carried by water that used to flow into the crater and tops made of sediments deposited by wind.

However, how the mounds formed inside craters that were once full of sediments was an open question.

"There's been a theory out there that these mounds formed from billions of years of wind erosion, but no one had ever tested that before," Day noted. "So the cool thing about our paper is we figured out the dynamics of how wind could actually do that."

To test whether wind could create a mound, the researchers built a miniature crater, filled it with damp sand and placed it in a wind tunnel.

They tracked the elevation and the distribution of sand in the crater until all of it had blown away. Eventually all that was left of the sediment was a mound -- which, in time, also eroded away.

"We went from a filled crater layer cake to this mounded shape that we see today," Day said.

To understand the wind dynamics, researchers also built a computer model that simulated how the wind flowed through the crater at different stages of erosion.

The mounds' structure helps link their formation to climate change on Mars, added co-researcher Gary Kocurek in a paper published in the journal Geophysical Research Letters.