Mile-high mounds on Mars were created by WIND over billions of years: Structures in craters also reveal when the water dried up

Mars' pockmarked surface may one day be home to humans, but some of its craters already hold skyscraper-like mounds.

Scientists now claim the mile-high structures were carved by strong Martian winds that battered the planet over billions of years.

And the location of these giant mounds even help the experts pin down when climate change caused water to dry up on the red planet.

Scientists say vast mounds inside Martian craters have been craved by the wind over billions of years. Gale Crater (shown), the landing spot of the Mars rover Curiosity, has a three-mile-high mound at its centre called Mount Sharp. The circle is the landing place of Curiosity and the blue line is its path

The findings, show the importance of wind in shaping the Martian landscape, a force which, on Earth, is overpowered by other processes, according to lead author Mackenzie Day, a graduate student at the Jackson School of Geosciences at the University of Texas at Austin.

'On Mars there are no plate-tectonics and there's 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,' she said.

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

Experts first spotted the awe-inspiring mounds at the bottom of craters during Nasa's Viking programme in the 1970s.

Recent analysis of Mount Sharp – a three mile high crater inside Gale Crater - by Nasa's Curiosity rover, revealed the thickest mounds are made of sedimentary rock.

It also found the bottoms are made of sediments carried by water that used to flow into the crater, while the tops are formed of sediments deposited by wind.

Mr Mackenzie told MailOnline: 'Layers at the base of intra-crater mounds are very old and potentially come from an early warmer period in Martian history.

'Our work suggests that these basal layers were covered, protected by hundreds of metres of overlying material, and then exposed again more recently at the surface.

'If early Mars was habitable, evidence of that habitable environment might be found at the base of these eroding mounds.'

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,' Ms Day said.  

The scientists made a model of a crater and mound to study the effects of wind. These images show sediment-filled craters on Mars (top) in different stages of erosion compared with results of a crater model in a wind tunnel experiment (bottom). Warm colors reflect high elevation, and cool colors low elevation

The findings show the importance of wind in shaping the Martian landscape. This image was taken by the Mast Camera (MastCam) on Nasa's Curiosity rover and highlights the interesting geology of Mount Sharp, a mountain inside Gale Crater, where the rover landed and the wind experiment was focused

'So the cool thing about our paper is we figured out the dynamics of how wind could actually do that.'

The researchers built a miniature crater 12 inches (30cm) wide and 1.6 inches (4cm) deep, filled it with damp sand and placed it in a wind tunnel, to test whether wind could create a tall mound. 

They tracked the elevation and the distribution of sand in the crater until all of it had blown away.

The team discovered the model's sediment was eroded into forms similar to those observed in Martian craters, forming a crescent-shaped moat that deepened and widened around the edges of the crater.

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,' Ms Day said.

The scientists also built a computer model to understand the wind dynamics.

They used it to simulate how the wind flowed through the crater at different stages of erosion.

Researcher Gary Kocurek said the mounds' structure helps link their formation to climate change on Mars, because their bottoms were formed during a wet time, while the higher parts of the mound were made and shaped by wind over time.

The bottom of the mounds were formed by water, while the top parts were crafted by wind. This image shows a view from the 'Kimberley' formation on Mars taken by Curiosity. The strata in the foreground dip towards the base of Mount Sharp, indicates water once flowed toward a basin that existed before the mountain formed

'This sequence signals the change from a dominance of depositional processes by water during a wetter time, to wind reworking of these water-laid sediments with the onset of aridity, followed by wind erosion once these sediment supplies have been exhausted,' he said.

'Overall, we are seeing the complete remaking of the sedimentary cycle on Mars to the one that characterises the planet today.'

The research helped scientists home in on the red planet's Noachian period - a geologic era that began about 3.7 billion years ago - as the period when Mars started to change from a wet world to a dry one.

They were able to link the climate change to the Noachian by studying the location of more than 30 mounds, finding that sedimentary mounds were only present on terrain that was exposed during that period. 

The findings are published in the journal Geophysical Research Letters.