Previous Evidence of Water on Mars Now Identified as Grainflows

James Marshall
November 22, 2017

"We've thought of RSL [recurring slope lineae] as possible liquid water flows, but the slopes are more like what we expect for dry sand".

NASA detailed the new study recently, saying the streaks shown in the image above are likely granular flows, not the subsurface water flows some had previously expected. The paper appeared in Nature Geoscience this week. Hydrated salts indicate that a small amount of water may be involved in the overall formation of these lines, though, just not to the degree that was previously speculated.

These features have evoked fascination and controversy since their 2011 discovery, as possible markers for unexpected liquid water or brine on an otherwise dry planet.

Dark flows streak down hills and craters on Mars each summer, before fading away in the colder months.

The team came to this conclusion by analysing the dark, narrow, down-slope trending surface features - referred to as recurring slope lineae (RSL) - mostly found on steep rocky slopes in dark regions of Mars.

Artist's conception of the complex magnetic field environment at Mars. This is based in part on assessments made with the Mars orbiter's telescopic camera. The data include 3-D models of slope steepness using pairs of images for stereo information.

The RSL are nearly all restricted to slopes steeper than 27 degrees.

The terminal end of the RSL slopes are identical to the slopes of sand dunes where movement is caused by dry granular flows, he said.

The team found that the streaks only existed at the top of steep slopes and flattened out like a pile of dry sand when the ground evens out.

"The RSL don't flow onto shallower slopes, and the lengths of these are so closely correlated with the dynamic angle of repose, it can't be a coincidence", said HiRISE Principal Investigator Alfred McEwen at the University of Arizona, Tucson, a co-author of the new report.

These findings indicate that it is hard for Earth-like life to exist near the surface of Mars owing to the water-restricted conditions that exist on the planet. While the surface of Mars immediately boils water due to its low pressure, we thought water stored underground might be seeping to the surface.

Other reports by Click Lancashire

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