The two Mars exploration rovers, Spirit and Opportunity, are each about the size of a golf cart. Their six-wheel undercarriages are designed in such a way as to allow a rover to climb over small rocks, and rotate in place. Lately, dust storms threatened to kill one of NASA's Mars rovers and stopped its twin in its tracks.

A slight clearing of still-dusty Martian skies has improved the energy situation for both Spirit and Opportunity, allowing controllers to increase the rovers' science observations.

At its lowest, Opportunity's power level was perilously close to dropping below the level needed to simply survive.

On the other side of the Red Planet, Opportunity's twin - Spirit - had enough power to move its robotic arm that day for the first time in almost three weeks. It used a microscopic imager on the arm to examine a rock and two patches of soil on the ground.

The rovers need power at night to heat their electronics in order to protect them from the potentially fatal cold. Rover engineers are not sure how much cold the rovers can take. Their electronics were tested on the ground prior to launch at temperatures as low as -55° C without damage, declared rover chief scientist Steven Squyres of Cornell University in Ithaca, New York, US.

The increased output from the solar panels has allowed Opportunity to fully charge its batteries and Spirit to bring its batteries to almost full charge.

Both rovers were in the areas which can contain crucial geological records of past conditions on Mars, that is why is so important to continue their survey. "Conditions are still dangerous for both rovers and could get worse before things get better," said John Callas, rover project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif.