Martian moats and mounds carved by extreme wind

The mysterious mounds of rock that reside in craters on the surface of Mars may be the result of extreme winds, during a time of significant climate change on the Red Planet.

A group of researchers at University of Texas used a physical model to simulate the winds on Mars, aiming to find the cause of the enormous crater-mounds – some of which are four kilometres high.

The mounds were first discovered in the 1970s, and theories as to their origins have circulated since.

“There’s been a theory out there that these mounds formed from billions of years of wind erosion,” explains Mackenzie Day, lead author of the paper.

“But no one had ever tested that before. The cool thing about our paper is we figured out the dynamics of how wind could actually do that.”

To test the wind theory, Day led a team of researchers in building a model of one of the planet’s craters, 30 centimetres wide and four centimetres deep – around the size of a cake tin.

The team filled the crater with damp sand and placed it in a wind tunnel, recording the position and movement of the sand until it had completely blown away.

Over time, the sand within the model crater eroded, creating a moat along one side. This moat eventually widened, leaving a mound in the centre of the crater. Eventually, the mound also eroded away.

Day says the surface of Mars is more significantly affected by wind than the surface of Earth, because we have other processes that work against it, such as water and tectonic plates.

“On Mars there are no plate tectonics, and there’s no liquid water, so you don’t have anything to overprint that signature. Over billions of years you get these mounds, which speaks to how much geomorphic change you can really instigate with just wind,” Day says.

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

The team says that while the model was not intended as a scale replica of the conditions on Mars, it does demonstrate the creation of a moat and resulting mound caused by levels of wind erosion similar to those on Mars.

Gary Kocurek, geologist and co-author of the paper, says the structure of the mound suggests it formed during a period of intense climate change around 3.7 billion years ago – a crucial chapter in the history of Mars, during which the planet’s atmosphere shifted from wet to arid.

Kocurek says the lower sediments within the mound point to a wetter period, while the higher sections signal a time of increasing aridity: “Overall, we are seeing the complete remaking of the sedimentary cycle on Mars to the one that characterises the planet today.”

The finding was published in Geophysical Research Letters.

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