Movement of sediment on ancient Mars may not have required water

Simulation shows alternate mechanism that required little water to transport surface material down slopes.
By Laurel Kornfeld | Nov 01, 2017
Features on Mars' surface that scientists have interpreted as indications of ancient flowing water could have been produced by sediment transport methods that did not require water, according to a new study published in the journal Nature Communications.

Researchers have long assumed that gullies, slopes, dunes, and dark streaks on the Martian surface were created by the downward flow of sediment carried by high levels of water that the planet later lost.

A key problem with this theory is the huge amount of water that would have been necessary to create these features, which is far more than would have been produced via Martian weather.

In a computer simulation that replicated atmospheric conditions on ancient Mars, scientists at The Open University determined high levels of sediment can be transported downward with much less water due to the planet's thin atmosphere, low pressure, and relatively warm surface temperature.

Mars' atmospheric pressure is about seven millibars as compared with 1,000 millibars on Earth.

Under low atmospheric pressure, water will boil at surface sediment temperatures of just five degrees Celsius. Boiling water can hover or levitate above the surface and draw high levels of sand and sediment down sloped terrain.

In the simulation, approximately nine times more sediment was transported down a slope with this "levitation" effect than without it.

Lower gravity, such as that on Mars, sped up the rate at which the sediment was transported over vast distances.

Although Mars' mean surface temperature is around minus 55 degrees Celsius, surface temperatures during Martian summer can reach 30 degrees Celsius.

The source of the water that could have produced this "levitation effect" remains unknown and requires further research. For scientists, however, the significance of these findings is confirmation of a possible sediment-moving mechanism on ancient Mars that did not require the large amount of water previously assumed to have been necessary for this process.

"Our research has discovered that this levitation effect caused by boiling water under low pressure enables the rapid transport of sand and sediment across the surface. This is a new geological phenomenon, which doesn't happen on Earth and could be vital to understanding similar processes on other planetary surfaces," study lead author Jan Raack of The Open University said.

"The sources of this liquid water will require more observational studies; however, the research shows the effects of relatively small amounts of water on Mars in forming features on the surface may have been widely underestimated."

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