NASA's Mars Exploration Rover Opportunity has spied a rock that could be a meteorite.

The dark rock is roughly 0.6 metres across and has been nicknamed "Block Island". It was first spotted on 18 July, in the opposite direction to which Opportunity was driving. The rover then received instructions from scientists on the Earth to alter its course by some 250 metres in order to study the rock in greater detail.

Opportunity will test the rock with its alpha particle X-ray spectrometer to determine its composition and thus conclude if indeed it is a meteorite.

Opportunity also lays claim to the first iron meteorite ever found on a planet other than Earth. That discovery was made in 2005 and since then the twin rovers have found at least half a dozen rocks from space with both iron-rich and stony compositions.