Spirit stops to investigate rock

Adirondack's dust-free surface is ideal for grinding

Nasa's Mars rover Spirit went for a drive on the Martian soil on Sunday and stopped to investigate a large rock.

The boulder - dubbed Adirondack - was chosen because its surface is flat and dust-free and therefore ideal to grind.

The Spirit rover will now pause by the football-sized object to conduct tests to determine its mineral make-up.

Spirit is the first of two identical US space agency probes that will spend 90 days on Mars studying the planet's rocks and soil for signs of past water.

Sunday's drive came two days after the rover rolled off its landing pad.

Project managers say the mission had gone so well they will consider extending it beyond the scheduled three months.

Fresh sample

We needed to decide which of these time capsules to open Dave Des Marais, Nasa

If they wish, Nasa scientists can now grind out samples of the rock with Spirit's rock abrasion tool (Rat), which is located on the rover's arm.

It uses three electric motors to drive rotating grinding teeth into the surface of a rock at high speeds.

Once a fresh surface is exposed, scientists can determine the rock's interior with other science instruments, such as the Mossbauer spectroscope and alpha particle X-ray spectrometer.

This can provide evidence of environmental conditions when the rock first formed.

Spirit's Sunday drive took approximately 30 minutes, including time to stop and take images.

The rover first made a series of arcing turns of about one metre (3 feet). It then turned in place and travelled about 2 metres (6.5 feet) forward in four moves.

"These are the sorts of baby steps we're taking," said rover mobility engineer Dr Eddie Tunstel.

Wheel slip

Mission engineers will now gather new information about how the rover moves on the Martian soil, such as how much the wheels slip on the surface.

Scientists chose Adirondack to be Spirit's first target rock over another rock called Sashimi that was more convenient to get to, because Adirondack's surface was relatively dust-free and less pitted than Sashimi's.

Scientists believe Adirondack could be composed of the volcanic mineral basalt, and that it was spewed on to the Martian surface hundreds of millions of years ago by a eruption.

Mission scientist Dr Dave Des Marais said rocks like Adirondack will help the science teams to better understand how the rock was formed and what the planet was like millions of years ago.

"We needed to decide which of these time capsules to open," he said.

Adirondack will also be a good test of Spirit's geology tools, which will then be used on other rocks and soils to establish a better database about the planet, Dr Des Marais said.

Spirit's twin rover Opportunity is expected to land on the Red Planet on 26 January GMT.