Aloha – Phobos isn’t a planet, it isn’t even that big as moons go, but it appears that Phobos’ days are numbered and that Mars by be down to one moon in the future.
The gravitational pull between the two bodies of Mars and Phobos is the source of the problem. The stress is causing fractures on the surface of Phobos, and the Moon creeps very slowly… closer to Mars.
The good news is that the disintegration of the moon is still measured in millions of years, but as the Solar System goes its not that far away… perhaps thirty million years from now.
Phobos is actually larger than its partner moon, Deimos at about 22 km in diameter. It’s orbit is a mere 3,700 miles from the surface as compared to our Moon that is a quarter million miles away.