Scientists believe that Phobos, one of Mars' two moons, is destined to be torn to shreds and form a ring around the Red Planet, and if so, it might be a fitting callback to how it got there in the first place. The mystery of the origins of the moons may have been solved by a new study that gives weight to the theory a huge collision between Mars and an ancient protoplanet resulted in the creation of Phobos and Deimos, as well as several other now-missing moons.
Two main hypotheses are debated regarding the birth of the Martian moons. One suggests that Phobos and Deimos were originally asteroids that became trapped in orbit about Mars. But a study, conducted by researchers in France, Belgium and Japan, suggests that the shape and orientation of their orbits, as well as the fine, grainy composition of the moons, makes that scenario unlikely.
There's a second, more explosive theory that Mars collided with a protoplanet about a third of its size between 4 and 4.5 billion years ago. The debris thrown up by that colossal impact formed a disk around the planet, which, over the course of millions of years, led to the formation of Phobos, Deimos, and other moons which no longer exist.