Space.com: One of Mars’s two moons, Phobossmall (average radius of 11 km), lumpy, and potato shapedwas probably formed from rubble shot into space after a comet or meteorite struck the planet, a new study has found. The research was presented at the European Planetary Science Congress in Rome and has been submitted to the journal Planetary and Space Science. Researchers, using data from the European Space Agency’s Mars Express spacecraft, base their conclusion that the two bodies have a common origin on the fact that Phobos and Mars share common minerals and phyllosilicates, among other things.