Could this be the next outpost in space? (Image: University of Arizona/NASA) Whether Phobos is a chip off the old Martian block, or a captured asteroid is still up for debate (Image: Detlev Van Ravenswaay/SPL)

Interactive graphic: Missions to Phobos

PHOBOS is a name you are going to hear a lot in the coming years. It may be little more than an asteroid – just two-billionths of the mass of our planet, with no atmosphere and hardly any gravity – yet the largest of Mars’s two moons is poised to become our next outpost in space, our second home.

Although our own moon is enticingly close, its gravity means that relatively large rockets are needed to get astronauts to and from the surface. The same goes for Mars, making it expensive to launch missions there too – perhaps even prohibitively expensive if President Obama’s review of NASA’s human space exploration policy is to be believed. Last October, a committee of independent experts chaired by industrialist Norman Augustine concluded that NASA faced a shortfall of around $3 billion a year if it still intends to send astronauts back to the moon – let alone Mars – by 2020. But that doesn’t mean that humans have nowhere to go.

One option the Augustine report suggested would take NASA crews to nearby asteroids and to the moons of Mars. “The bulk of the cost of a Mars mission is getting people to the surface and back again,” says Pascal Lee, chairman of the Mars Institute in Moffett Field, California. “If you wait for everything to be ready, it will be decades. Phobos offers us a way to get to the very doorstep of …