Dust storms that threatened to kill one of NASA's Mars rovers and stopped its twin in its tracks have abated somewhat.
One of the rovers, Opportunity, was poised to enter the 800-metre-wide Victoria crater, which may contain crucial geological records of past conditions on Mars, when the storms hit in late June.
Lofting dust high in the atmosphere, the storms have blocked precious sunlight needed for the rover solar panels to generate power. Opportunity was not only prevented from entering the crater, but was so starved of power that its handlers worried it might freeze to death during the cold Martian night (see Worsening dust storms threaten Mars rovers).
Now, the storms have cleared a little, giving the rovers some breathing room. As of 5 August, Opportunity was getting 243 watt-hours of power per day from its solar panels, up from a low of 128 watt-hours in mid-July. Before the onset of the storms, Opportunity was getting 700 watt-hours per day.
At its lowest, Opportunity's power level was perilously close to dropping below the level needed to simply survive. The rovers need power at night to heat their electronics in order to protect them from the potentially fatal cold.
Mindful of this hazard, the rover team took the extreme measure of ordering Opportunity to cut back on communication with Earth in order to save power.
Despite the power saving measure, the team was worried about Opportunity's electronics last week when their temperature dipped to -37° C. Their temperature has since risen slightly to -33° C.
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, says rover chief scientist Steven Squyres of Cornell University in Ithaca, New York, US. "But -55 is a number we don't want to get close to if we can avoid it," he told New Scientist.
With skies somewhat clearer above Opportunity, it has been able to fully charge its batteries, which the rover can draw on temporarily if solar power is not meeting its needs. Its power level is high enough that the rover team plans to use some of its energy to carry out science observations of the atmosphere.
On the other side of the Red Planet, Opportunity's twin, Spirit has had an easier time of it. Its power level has never dropped below 260 watt-hours per day, and it was up to 295 watt-hours by early Monday.
It 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.
But the rover team has not let its guard down yet. "Conditions are still dangerous for both rovers and could get worse before things get better," says rover project manager John Callas of NASA's Jet Propulsion Laboratory in Pasadena, US.
No matter what the storms do, Opportunity's descent into Victoria crater will be a long way off. The very fine-grained dust that has been lifted into the atmosphere takes a long time to settle, Squyres says: "Even if all the winds on Mars stopped blowing tomorrow, it would be a matter of weeks, not days, before the skies cleared substantially."
Mars Rovers - Mars is full of surprises, learn more in our continually updated special report.
If you would like to reuse any content from New Scientist, either in print or online, please contact the syndication department first for permission. New Scientist does not own rights to photos, but there are a variety of licensing options available for use of articles and graphics we own the copyright to.