Nasa has upgraded the software on its Mars rovers to provide new capabilities as the machines roam across the planet.

New software was broadcast from Earth over the new year, relayed via the Deep Space Network satellite system and installed on the Spirit and Opportunity rovers.

The upgrade offers four new functions, including better pattern recognition and improved self-navigation. 

"These rovers are a great resource for testing software that could be useful to future Mars missions without sacrificing our own continuing mission of exploration," said Dr John Callas, project manager for the Mars Exploration Rovers.

"This new software will be a baseline for the development of flight software for the Mars Science Laboratory, but is also helpful in operating Spirit and Opportunity. "

Upgrades include better object tracking so that the rovers can remember the location of barriers more easily. New code has also been added that will allow the rovers to choose where to use their ground probing tools without human control.

This is the fourth software upgrade sent to the rovers, following one beamed over while they were in flight and two carried out after landing.

The rovers were originally expected to last for three months, but 3 January will be Spirit's fourth year of exploration.