Something awful is happening to the largest moon of Mars
Deep, scar-like grooves wind all the way around the Martian moon Phobos, and now scientists think they mean something ominous: The tiny moon is slowly being shredded into pieces.
"We think that Phobos has already started to fail, and the first sign of this failure is the production of these grooves," said NASA scientist Terry Hurford in a press release.
You can see the grooves in the image below. They're especially prominent in the top right area:
Phobos, which is roughly the size of the length of Manhattan, will likely meet an early demise because it's unusually close to Mars. According to NASA our moon is nearly 239,000 miles from Earth, but Phobos is only about 3,700 miles away from Mars.
The closer distance means Martian gravity is tugging exceptionally hard on Phobos - it's pulling the moon closer by about 6.6 feet every year. At that rate, scientists estimate Phobos will slowly crumble under the force, break apart completely in the next 30 to 50 million years, and vanish.
Previously, scientists thought the grooves on Phobos came from an ancient meteor strike. That meteor crashed in Phobos and left a deep hole called Stickney crater. It appeared that the grooves were fracture lines coming from the crater.
Here's what that crater looks like:
However, Hurford and his team noticed that the grooves didn't originate at the crater. Models show that they are more likely "stretch marks," or cracks that appear as Phobos gets deformed by Mars' gravity.
Some moons are strong enough withstand the gravitational pull from their planets. The Earth and the moon both exert a gravitational force on each other called tidal force. Tidal force is the reason Earth's oceans have tides and why the Earth and the moon are slightly egg-shaped rather than perfectly round.
But unlike our moon, Phobos has a very weak core. NASA scientists think it's just a pile of rubble coated with dust. So the tidal force generated between Mars and Phobos is causing the fragile moon to crack open. It's uncertain if the same thing is happening to Deimos, Mars' only other moon. (It orbits the planet about 2.5 times farther away than Phobos.)
The research could help us better understand planets outside our solar system, since the same thing can happen to planets that are being pulled toward their host star.