It looks like a glowing speck or star moving swiftly around the surface of Mars. The tiny moon Phobos orbits the red planet in a new time lapse video released by NASA. The Hubble Space Telescope captured a series of 13 images of Mars over the course of 22 minutes on May 12, 2016—at a time when the red planet was 50 million miles from Earth—and Phobos unexpectedly stole the spotlight.
Phobos orbits Mars at a distance of about 3,700 miles, closer than any other moon in the solar system to its parent planet. It’s also one of the smallest. With dimensions of 16.5 miles by 13.5 miles by 11 miles, however, the “diminutive, potato-shaped moon,” as Hubble’s website calls it, is larger than its Martian moon sibling, Deimos.
The American astronomer Asaph Hall discovered both in August 1877 at the U.S. Naval Observatory in Washington, D.C. They’re named after the sons of Ares, the Greek god of war whose equivalent in Roman mythology is Mars. “Phobos” means panic or fear (think “phobia”) while “Deimos” means dread or or terror.
The time lapse video of Phobos on its seven-hour-and-39-minute orbit of Mars is more likely to inspire wonder than fear. But here’s something that might shift viewers toward the latter. NASA has said that the larger of Mars’ two moons is in the long, slow process of being destroyed. The shallow grooves visible in close-up images of its surface are a sign of structural failure.
“We think that Phobos has already started to fail, and the first sign of this failure is the production of these grooves,” Terry Hurford of NASA’s Goddard Space Flight Center in Greenbelt, Maryland, said in a statement in 2015. He and his colleagues explained the grooves as stress fractures created by Mars’ tidal forces acting on a moon that is actually a pile of rubble being held together by a thin crust. Phobos is getting about 6.5 feet closer to Mars every 100 years, and scientists predict that it will be destroyed within 30 to 50 million years by crashing into its parent planet or scattering into a ring around it.
While Phobos is still intact, it could provide a stepping stone toward human exploration of Mars. The Planetary Society released a report in 2015 suggesting an astronaut mission to Phobos in 2033 as a precursor to a Mars landing a few years later. The plan calls for a crew to make history with a 300-day stay in a prepositioned habitat on the Martian moon, the same one that made a surprise appearance in Hubble’s images.