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Sand Grains, Instead of Water, on Mars!

S u m m a r y :
Previously identified Martian water is actually sand and dust, suggests a new study that challenges previous ones. The findings are published in the journal Nature Geoscience.

Water or Sand?

Mars does not have that much water, after all—scientists mistook sand and dust for flowing water. Certain dark features on Mars were, previously, thought as indicative of significant volumes of liquid water, but these have now, been interpreted differently: granular flows made of sand and dust. This implies that Mars does not even have adequate water for life to exist as it does on our planet.

Examining Martian Slopes

This conclusion comes from the analysis of the said Martian features, called Recurring Slope Lineae, or RSL, by a team of investigators from the U.S. Geological Survey (USGS), the University of Arizona, Durham University (England), and the Planetary Science Institute. RSL features are known to grow and fade, recurring annually during the Martian ‘summer’. They are normally situated on steep slopes in dark regions, like the southern mid-latitudes, and near the equator at Valles Marineris. How have they been mistaken for water? According to the authors of the new study, their appearance and growth make them look like flowing liquid water, but they are more likely to be granular materials like sand and dust in movement.

“We’ve thought of RSL as possible liquid water flows, but the slopes are more like what we expect for dry sand,” says lead author Colin Dundas from USGS. “This new understanding of RSL supports other evidence that shows that Mars today is very dry.”

Recurring Slope Lineae on Mars (enhanced color). Notice the dark flows moving downhill on the upper left of the picture. These flows all end on the same slope, suggesting the presence of sand, and not water. Photo Credit: NASA/JPL/University of Arizona/USGS.

Dundas explains that the ends of the RSL slopes are similar to slopes of sand dunes; these slanted areas are characterised by movement caused by dry granular flows, and not substances like water. If it were the latter, it would mean that its volume would have to be comparative to the length of the slope, leading to more liquid on taller ones. However, the RSL that were analysed would end on approximately the same slope, regardless of the varying lengths.

Martian Water in Limited Quantity Only

Another element that rules out water is that it is very unlikely to be formed only at the tops of slopes at the angles observed; if it was actually produced there, it would have flown onto lower slopes.

This study favours the old theory that Mars does not have flowing water on its surface. But, this does not mean that there is absolutely no water on Mars. Rather, as point out the Dundas and his colleagues, hydrated minerals have been identified in some RSL regions, and any liquid on Mars today would be in the form of traces of dissolved atmospheric moisture, and thin water films.

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