Phobos, Mars’ largest moon — although at just 16 miles wide still quite small — is slowly but steadily being torn apart by the gravitational pull of Mars… and it bears the scars to prove it. Long parallel grooves seen wrapping around the surface of Phobos are most likely stress fractures, visible evidence of the tidal forces that will one day cause the moon to break apart entirely. And when it does it will create a temporary ring of rubble and dust around Mars making our rusty red neighbor resemble a miniature Saturn.
At least for anywhere from one to a hundred million years, but hey—even Saturn’s majestic rings are thought to be just a fleeting feature on a cosmic time scale.
Astronomers have long known that Phobos, the larger and nearer of the two martian moons, is slowly spiraling inward to eventual destruction. The end result won’t be pretty: Phobos will slip closer and closer toward Mars, then strike a gravitational line where the planet’s tidal forces will be strong enough to rip it apart. The rubble pile-like moon will break into smaller boulders, rocks, and dust, and will spread out in orbit around Mars. Mars will join the gas giants in having a spectacular feature: a ring system.
It could be 25 million years from now. It could be up to 75 million years. Recent discoveries about the little moon’s composition and density, however, make it far more likely that its death dive will happen sooner. The pieces that don’t form a ring will fall to the surface, smashing with enough force to pockmark Mars with new craters.