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Mars moon Phobos is doomed to fall apart from stress

Phobos is very close to its planet Mars, but the intimacy of that relationship also means destruction for the moon, NASA says this week.

NASA's new modeling efforts show that Phobos' grooves could be caused by tidal forces.
NASA/JPL-Caltech/University of Arizona

Unlike Saturn, Mars doesn't have many moons to spare. The ringed planet sports over 60 moons. Mars has just two, Deimos and Phobos. According to NASA, Phobos is on track to be pulled apart within 30 to 50 million years, a relative blip on the time scale of the universe.

Scientists figured out Phobos' fate by viewing images of the moon that show a series of grooves along its surface, and they shared their insights on Tuesday. "We think that Phobos has already started to fail, and the first sign of this failure is the production of these grooves," NASA's Terry Hurford said in a statement.

Phobos hangs out just 3,700 miles (6,000 kilometers) above the surface of the Red Planet, which means it snuggles up closer to its planetary buddy than any other moon-planet combo in the solar system. For comparison, our moon is around 238,900 miles (about 384,500 kilometers) away from Earth. NASA likens the visible grooves on Phobos to "stretch marks" from tidal forces deforming the moon.

This isn't the first time this theory has popped up. It also arose in 1976, when the Viking spacecraft took images of Phobos, though scientists dismissed the idea on the assumption the moon was solid.

But scientists have reevaluated the structure of the moon and now believe it may have a pile of rubble in its interior, rather than being a solid chunk all the way through. That lends credence to the idea that the gravitational pull from Mars could be distorting it out of shape.

A NASA image of Phobos makes for a fascinating study. It shows an irregular surface pockmarked with craters, including the very large Stickney crater, the result of an impact so strong it nearly broke the moon up right there and then. The grooves appear as long, shallow lines running across Phobos like someone dragged brush bristles over the surface.

Phobos is doomed. So what would a Mars moon have on its bucket list? Perhaps it would like to live long enough to see humans arrive on Mars. Or maybe it would like to make friends with that woman-shaped rock that alien theorists got all excited about earlier this year. At least it has millions of years ahead to figure it out.