Asteroid 2000SG344 is just 40 metres across, but could become the second extra-Terran object explored by humans.

Nasa plans a return to the moon somewhere in the 2020 timeframe, with trips to Mars following around a decade later.

But a 3 month mission to an asteroid would make a practical stepping stone in preparation for the red planet.

The asteroid is particularly suitable, as it regularly swings close to Earth. Exploring the rock would offer insights into preventing asteroid collisions with Earth, as well as serving up some original eye-candy for the space program.