The robot scouring the Antarctic ice for meteorites has tracked one down.

The small space rock was identified on Saturday and shows the robot can use its sensors to automatically tell the difference between meteorites and Earthly pebbles.

Dimi Apostolopoulos, manager of the Nomad project at Carnegie Mellon University's Robotics Institute, said it was a "tremendous result".

Researchers had already seen the meteorite whilst walking over the test area, but the robot, called Nomad, found, analysed and classified the rock all by itself.

Quite confident

Using visual and spectroscopic data, Nomad came up with a 22% confidence value that the rock was a meteorite. The robot found seven other rocks during the sweep and correctly identified them as terrestrial - the average confidence values was 5%.

Team member John Schutt verified that the rock with the high confidence value was indeed a meteorite. He said the meteorite was an ordinary chondrite, measuring 4 by 5 by 6 cm (1.5 by 2.0 by 2.4 inches).

According to Mr Apostolopoulos, these results show what confidence values suggest a rock is of extraterrestrial origin. Nomad's ability to spot meteorites with greater confidence will improve as more diverse specimens are examined, he added.

After the discovery, Nomad returned to base and underwent more tests of its analytical equipment. It has now returned to the open ice and is once again searching for meteorites. The tests will continue until 30 January.

Beach buggy

Nomad may have the appearance of beach buggy, but it represents a significant step forward in robotics and could pave the way to a new kind of mission to Mars and the Moon.

The robot is trundling around Elephant Moraine, a remote area in eastern Antarctica, 260 kilometres (160 miles) northwest of the US base at McMurdo Station.

Elephant Moraine is regarded as one of the more important sites for meteorite discovery, with thousands of specimens already recovered during previous expeditions, including the first meteorite identified as definitely being from Mars. Nomad's expedition is taking place near an area last searched in 1979.

It has stereo cameras to give it a sense of the surroundings as it hunts for rocks distinguished by their dark colour against the white ice background. A high-resolution camera is used to zoom in on interesting specimens. A spectrometer then analyses the light reflected off a particular rock to determine its composition and whether it is a likely meteorite or not. A metal detector will pick up any iron content, an important component of some space rocks.

If Nomad thinks a specimen is a meteorite, it will radio the object's exact location to the researchers using co-ordinates calculated by the satellite-based Global Positioning System. The project team can then pick up the rock at a later time.

This is Nomad's fourth expedition overall, but the first on which it was expected to move and analyse specimens completely on its own. Previous outings, in Antarctica and Chile's Atacama Desert, have been used only to test systems.

If the Elephant Moraine expedition succeeds, the project scientists hope the technology will be picked up by Nasa for future missions to other worlds.