Spirit completes primary mission

The rovers will spend 150 days longer on Mars than expected

Nasa's robotic Mars explorer Spirit has completed 90 days on the Red Planet, the last of the criteria it needed to meet for success of its mission.

The US space agency's robot rover landed in Gusev Crater, near Mars' equator, on 4 January to look for past or present signs of liquid water.

It succeeded in this task, identifying evidence of water flow in the structure of rocks at its landing site.

Spirit has now travelled more than 600m (1,969ft) on the Martian surface.

But that will not be the end of Spirit's work on Mars.

Last month, Nasa confirmed that both Spirit and its twin rover Opportunity would work for up to 240 days on the Red Planet, about 150 more than the mission team had originally projected.

Mission engineers analysed power data for Spirit and Opportunity which showed the vehicles were performing much better than they had expected.

It meant the rovers could keep scouting Mars for interesting rocks that could reveal more about its watery past.

Spirit is now heading for a patch of high ground mission scientists have called Columbia Hills. Nasa believes the hills may reveal layering that could give scientists information about the formation of Gusev Crater.

Researchers think the crater once held a lake, but much of the evidence for this watery past may have been concealed by Mars' shifting dust.

Spirit will stop along the way to examine rocks and features of interest to mission controllers.