NASA

As NASA moves forward with its plans to reach (and one day colonize) Mars, we are learning more and more about the Red planet. Like, it has water! And it's moon, Phobos, is slowly but surely falling apart.

"We think that Phobos has already started to fail, and the first sign of this failure is the production of these grooves,” said NASA's Terry Hurford in a statement.

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According to research done by Hurford and a team of fellow astronomers, the grooves that characterize Phobos are a result of the gravitational pull Mars exerts on the satellite. NASA explains that Phobos core is little more than "a rubble pile, barely holding together, surrounded by a layer of powdery regolith about 330 feet (100 meters) thick." The moon's top layer is likely quite elastic—so Mars' pull on Phobos makes, in NASA's words, "stretch marks." One day, that pull will force the moon apart.

The findings were discussed this week during the annual Meeting of the Division of Planetary Sciences of the American Astronomical Society, which is happening this week. In an abstract, Hurford and his team explain:

Phobos is steadily spiraling inward due to the tides it raises, and will suffer tidal disruption before colliding with Mars. We calculate the surface stress field of the de-orbiting satellite and show that the first signs of tidal disruption are already present on its surface. Most of Phobos’ prominent grooves have an excellent correlation with computed stress orientations.

NASA's 1970s-era Mars missions, Viking 1 & 2, suggested that the grooves might be coming from Mars' pull. But scientists dismissed this possibility at the time because they thought Phobos was solid throughout, and therefore couldn't be so drastically affected by Mars' gravity.

Phobos, however, will stay intact for another 30 to 50 million years. Phew.

Danielle Wiener-Bronner is a news reporter.