Phobos (moon) break up when it reaches approximately 2.1 Mars radii. When Phobos is eventually torn apart by tidal forces, a fraction of the debris will likely form a planetary ring around Mars, which may last from one million to one hundred million years. The origin of the Martian moons is still controversial. Phobos and Deimos both have much in common with carbonaceous C-type asteroids, with spectra, albedo, and density very similar to those of C- or D-type asteroids. Based on their similarity, one hypothesis is that both moons may be captured main-belt asteroids. Both moons have very circular orbits which lie
Moons of Uranus less than half that of Triton (the seventh-largest moon in the Solar System) alone. The largest of the satellites, Titania, has a radius of 788.9 km, or less than half that of the Moon, but slightly more than that of Rhea, the second-largest moon of Saturn, making Titania the eighth-largest moon in the Solar System. Uranus is about 10,000 times more massive than its moons. As of 2016, Uranus is known to have 13 inner moons. Their orbits lie inside that of Miranda. All inner moons are intimately connected to the rings of Uranus, which probably resulted from the fragmentation