Scientists Explain 'Scratch Marks' on Mars
Levitating dry ice causes deep gullies: scientists
By Arden Dier,  Newser Staff
Posted Oct 27, 2017 11:47 AM CDT
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These lines of Mars' surface are believed to be caused by levitating dry ice.   (NASA)

(Newser) – No, a giant cat has not been clawing at the surface of Mars, though it might look like that. According to scientists, "scratch marks" or linear gullies on the Martian plains of Hellas Planitia were caused not by life forms but by dry ice—in fact, levitating dry ice. It's not magic: During Mars' winter, carbon dioxide gas in the atmosphere turns solid and is imbedded in the red planet's soil. During summer, the reverse process takes place. The deposits break apart and slide over dune slopes, levitating in the process as the dry ice in contact with the warm sediment turns back to gas, per a release. This results in the gullies, which were spotted by the Mars Reconnaissance Orbiter in a 1,400-mile-wide crater deeper than the Grand Canyon, reports CNET.

To figure this out, scientists from Trinity College Dublin put a Martian-like soil sample under low pressures and temperatures in the lab to mimic Mars' atmospheric conditions, then added water, they explain Scientific Reports. The water immediately evaporated and, for a few seconds, caused soil it had contacted to levitate, reports New Scientist. On Mars, where gravity is weaker, researchers believe the effect could last for up to a minute, plenty of time for an ice block to "levitate and maneuver downslope, in a similar manner to how pucks glide on an ice-hockey table, carving a channel in its wake," says study author Lauren McKeown. The block eventually disappears "without a trace other than the roughly circular depression beneath it." (Mars also has what looks to be a bullet hole.)

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