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NASA
The surface of Mars' largest moon, Phobos, is covered with huge grooves that could have been caused by huge rocks that rolled over its surface as a result of the impact of an asteroid.
According to Kenneth Ramsley of Rhode Island's Brown University, there are other planets and moons with similar ditches and scratches, but none are as covered as Phobos – the lunar grooves are 30 km long and 200 meters long. wide.
Ramsley and James Head, also at Brown, used a simulation of the Phobos-Mars system to examine whether these gorges could come from rolling stones.
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The pair said that these stones would have been ejected from the Stickney Crater, which was formed when a rock of about a kilometer sank on Phobos about 150 million years ago.
Phobos is small and close to Mars, the gravity of the planet would have acted on the rocks, so that some turn around the moon and creating secant lines that we see on its surface today. The whole process would have taken less than 12 hours after the impact, Ramsley says.
There is an area on the moon with almost no lines at all. The simulation showed that because this area had a lower altitude and that Phobos had a low gravity, the rocks would have simply rolled into space before coming back to the surface, like a cartoon character springing from a cliff. then landing on the other side.
But there is a problem: we do not see any rock on the surface. Ramsley said that this too can be explained by the debris of Stickney's impact. "Any extra debris that does not stay on the surface is trapped in orbit around Mars and returns to the crime scene within 1,000 years and hits Phobos again," he says. This bombardment could break the rocks and hide the smallest furrows under a layer of dust.
Journal reference: Planetary and space sciences, DOI: 10.1016 / j.pss.2018.11.004
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