Mars Moon Phobos Is Falling Apart

One of Mars' two moons, Phobos, is falling apart.

That is, NASA said in a recent release that lengthy, shallow grooves along that moon's surface likely indicate structural failure that will increase.

Currently that moon is orbiting about 3700 miles above Mars. It is nearer to its planet than any other moon in our solar system. Every hundred years, Mars' gravity sucks Phobos nearer by about 6.6 feet. Phobos is the larger of the two moons. In 30 to 50 million years, scientists believe it will have been knocked apart by all that gravity, the release confirmed.

It's also possible that tidal forces--caused by gravity on the planet and on the moon--are causing the grooves, according to new modeling, said NASA in the release. That differs from the previous hypothesis, which was that a huge impact, the same one that caused Stickney crater, formed the grooves. But later the scientists realized that the grooves don't radiate from the crater, but from a different point nearby.

"We think that Phobos has already started to fail, and the first sign of this failure is the production of these grooves," said Terry Hurford of NASA's Goddard Space Flight Center, in the release.

Hurford and colleagues recently presented their findings at the annual Meeting of the Division of Planetary Sciences of the American Astronomical Society, at National Harbor, Maryland.

According to the new modeling, the grooves likely are "stretch marks" from the pull of both Mars and the moon. That pull also makes both the planet and the moon slightly egg-shaped. While this was proposed decades ago, it was thought then that Phobos was fairly solid clear through, and that the movement was not strong enough to affect a solid moon. Now, though, scientists believe that Phobos might have a rubble center, surrounded by powdery regolith (or outside), as an article in CNet confirmed.

It may be that Neptune's moon Triton will also deteriorate, because it has a similarly fractured outside, the release confirmed.

"We can't image those distant planets to see what's going on, but this work can help us understand those systems, because any kind of planet falling into its host star could get torn apart in the same way," said Hurford in the release.

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