To boulder go on mission to Mars

A Nasa robot ship will pluck a large boulder off an asteroid and sling it around the moon, becoming an ad hoc destination to prepare for future human missions to Mars, the US space agency said.

The so-called Asteroid Redirect Mission is estimated to cost about $1.25bn (€1.14bn), not including launch costs, and is targeted for lift-off in December 2020.

It would be followed five years later by a human expedition to the space rock, a modification of a plan proposed by President Barack Obama in 2010.