Phobos Ripped From Mars?

A new study using data from the European Space Agency's Mars Express spacecraft argues that the Martian moon Phobos formed after something large struck Mars, sending material from the planet into space. A similar scenario is thought to have led to the formation of Earth's Moon.

Data shows that the material making up Phobos is similar to what makes up Mars, as opposed to the composition of asteroids; a leading theory of the origin of Phobos and Mars' other tiny moon, Deimos, has been that they were asteroids somehow captured by Mars' gravity.

The study also shows that the density of Phobos is extremely low, which again suggests a body loosely flung together as opposed to a solid body. Indeed, Phobos' density is so low that there must be huge caverns under the surface. That could be a big break for the future exploration of Mars. A manned base under the surface of Phobos, protected from radiation by miles of rock all around, might be the ideal place from which to direct the first comprehensive surface exploration of Mars.