Scientists have reason to believe that Phobos, Mars’ largest moon, is breaking apart. New modeling indicates that the moon’s many grooves are in fact the result of antagonistic gravitational pulls created by Mars and by Phobos itself. Eventually, this may result in the complete structural failure of the moon.

Astronomers have known for quite some time that Phobos is the victim of gravitational pressures. The moon orbits only 3,700 miles away from Mars- by far the closet orbital path of any moon in our solar system. Every hundred years or so, Phobos moves 6.6 feet closer to Mars as the planet slowly gains the upper hand in a eons-long struggle.

Yet a recent report presented today at the annual Meeting of the Division of Planetary Sciences of the American Astronomical Society at National Harbor, Maryland argues that the long, shallow groves on Phobos’ surface indicate that the moon is already starting to be pulled apart.

“We think the grooves are signs that this body is starting to break apart tidally and that these are the first evidence of the tidal deformations of Phobos,” said Terry Hurford of NASA’s Goddard Space Flight Center. “Eventually, Phobos will be ripped apart before it reaches Mars’ surface.”

Prior to this announcement, conventional wisdom held that the grooves were caused by either the massive impact of the asteroid strike that created the Stickney crater or else by many smaller impacts of material issued from Mars.

Yet, Hurford’s research suggests that the grooves are actually far more similar to stretch marks than to impact markings. Moreover, the interior of Phobos may be no more than a pile of rubble barely sticking together. This causes the surface of Phobos to behave elastically as it readjusts to the stress.

The strong gravity of Mars is pulling Phobos towards it while at the same time the moon is trying to pull away. The Earth and its moon affect each other in a similar manner but not nearly so dramatically. Indeed it is this subtle opposition between the Earth and Moon that causes the ocean tides.

It is believed that one of Neptune’s moons, Triton, will ultimately suffer the same fate as Phobos.

“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.