Dunes on Mars move just like on Earth
Sands of time A new study has found sand dunes on Mars are at least five times more active than earlier estimates, being comparable to dune movement rates on Earth.
The findings by researchers including Dr Nathan Bridges from the Johns Hopkins University in the United States, means a rethink of current models for past atmospheric conditions on the red planet.
The Martian atmosphere today has just one per cent the density of Earth's, which scientists believed was too thin to move sand grains.
So signs of wind erosion on the red planet, is evidence of a thicker atmosphere in the past.
However recent observations have shown signs of fresh sand dune movements on Mars, indicating the process is still happening today.
Bridges and colleagues used high resolution images from NASA's Mars Reconnaissance Orbiter.
They measured the movement of sand ripples on the Nili Patera dune field in the northern caldera of a volcanic complex on the border between the Martian northern lowlands and southern highlands.
Reporting in the journal Nature, Bridges and colleagues took images of the same area 105 Earth days apart, finding movement in the sand ripples extending across the entire dune field.
Their measurements indicate the Martian dunes are moving the same volumes of sand as Antarctica's Victoria Valley.
Contrary to previous models of the Martian atmosphere, the new findings mean conditions on Mars are sufficient to transport large amounts of sand.
Bridges and colleagues say this suggests possible fundamental differences in how sand is mobilised on Mars compared to the Earth.
They say once wind gusts start sand grains skipping across a dune on Earth, the grains will keep skipping even if the wind speed drops by a fifth.
However the different conditions on Mars will cause sand grains to roll at higher speeds, allowing them to keep going even if wind speeds drop by 90 per cent.
Bridges and colleagues also report huge differences in the time it takes sand dunes to form on Mars compared to Earth.
They say the Nili Patera dunes have 1000 times the volume of those in Antarctica's Victoria Valley, yet similar rates of sand movement.
This indicates the characteristic timescales of formation are 1000 times longer, showing that dunes on Mars evolve much more slowly than their counterparts on Earth.
Sand dune expert, Professor Robert Wasson from the National University of Singapore, says the findings paint an intriguing picture of the red planet.
"The comparison with Antarctica's Victoria Valley is interesting because while both places are extremely cold, the air in the Antarctic is far denser than Mars today," says Wasson.
"Whether on Earth or Mars, the air must be reasonably dense to move sand across a dune".
"And you still need wind speeds to reach a significant threshold to get the sand moving in the first place," says Wasson.
"But clearly the evidence is there to show the Martian sand is moving, so despite the thin atmosphere, the wind velocity and density are still sufficient on the red planet to achieve this."