New Mars robot rolls out to cheers

Nasa's exploration of the red planet took a second giant step forward yesterday when the robot explorer Opportunity joined its sister craft on the surface of Mars.

Engineers at Nasa's Jet Propulsion Laboratory in Pasadena, California, erupted in cheers as confirmation came through that the six-wheeled robot had successfully moved down its ramp. An old hit by the rock group The Who, "Going Mobile", accompanied the news.

"Two for two, one dozen wheels on soil," was how the flight director Chris Lewicki put it as Opportunity joined its twin on the planetary surface.

It followed Opportunity's discovery hours earlier of grey hematite, a mineral that typically forms in water - a finding that could indicate the dry and dusty planet was once wetter and more hospitable to life.

A single black and white image transmitted via satellite back to Earth showed the empty lander behind Opportunity and a parallel set of tracks leading away from it (pictured right).

The operation went as planned, a Nasa spokesman said, with the robot coming to a halt short distance away.

The rovers are on opposite sides of the planet to each other. Spirit is sitting in Gusev Crater, which may have once held a lake.

The mission of Opportunity and Spirit is to explore the rocks and soil of their landing sites for evidence of past wet environments.