Washington

After landing on Mars on 3 January, NASA's Spirit rover is now flexing its mechanical limbs and surveying its surroundings before heading out to explore. Scientists and engineers at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California, who operate the desk-sized robot, are itching to investigate the various features seen in the pictures of the martian surface returned by the rover.

Based on those preliminary images, Steve Squyres, a planetary scientist at Cornell University in Ithaca, New York, and principal investigator for Spirit's scientific instruments, speculates that the rover has landed in a field of small craters at the centre of Gusev Crater, which is thought to be an ancient lake bed.

The terrain around the landing site is pocked with shallow depressions, which Squyres says may be secondary impact craters caused by material falling back to the surface after being thrown up by a larger impact. One such pit, which the Spirit team calls 'Sleepy Hollow', is likely to be the robot's first destination, as it looks to contain a rock outcrop that could offer insight into sedimentary history.

The rover had the good fortune to land in what Squyres called “the place where we absolutely wanted to be”. The site is relatively free of boulders that would impede the robot. So mission controllers can bask in the smooth, early operation of what was seen as a make-or-break mission for the JPL, which suffered embarrassing back-to-back failures in 1999 (see Nature 423, 477; 2003 ).

Europe's first planetary orbiter, Mars Express, is also off to a promising start, with two successful orbit manoeuvres already under its belt, and another scheduled for this week to bring it closer to the planet's surface. Agustin Chicarro, the European Space Agency's project scientist for the mission, says that data from the onboard instruments should begin flowing in late January.

One of the spacecraft's key instruments, a ground-penetrating radar that aims to map water and ice to depths of several kilometres below the martian surface, will be deployed in late February. By April, says Chicarro, Mars Express should settle into a schedule of routine scientific observations.

James Head, a planetary geologist at Brown University in Providence, Rhode Island, says that if the Mars Express radar works as advertised, it could shed light on what happened to the large reservoirs of water thought to have existed in the planet's distant past.

A second NASA rover, called Opportunity, is set to reach Mars on 24 January. That leaves the British-built Beagle 2 lander as the only troubled mission in the current invasion of Mars (see Nature 427, 5; 2004 10.1038/427005a ). Project managers hope that Mars Express can make contact with Beagle 2 sometime after 7 January. High-resolution cameras on NASA's orbiting Mars Global Surveyor have also been enlisted to take close-ups of the lost craft's landing site.