NASA's newly upgraded Spirit rover will celebrate its third anniversary on the Martian surface hunkered down to weather a dust storm.
The rover parachuted down to Mars's Gusev Crater on 3 January 2004. Its twin, Opportunity, caught up and landed on the other side of the planet 21 days later.
Early last week, Spirit's instruments detected hazy conditions due to a large dust storm to the south that was churning up fine dust grains high in the atmosphere.
Because the storms block some sunlight from reaching the planet's surface, they could be dangerous for the rovers, which rely on solar power to generate electricity.
So on Thursday, ground controllers had Spirit stop taking scientific measurements of an igneous rock named Esperanza and scurry over to a slope tilted 7.4° to the north to maximise the amount of sunlight falling on its solar arrays.
"We had to boogie on out of Esperanza," says Ray Arvidson, deputy principal investigator for the rovers' science instruments at Washington University in St Louis, US.
'Lily pad' approach
At one point, its solar arrays were able to generate only 267 watt-hours per day. Rover principal investigator Steve Squyres of Cornell University in New York, US, said controllers would start worrying about the rover's safety if the power dipped to 250 watt-hours.
"267 was way too close for comfort," Arvidson told New Scientist. "That's why we had to get to another site."
Moving to the new slope increased its energy output by 30 watt-hours - a crucial boost, since the Sun is still low on Mars's horizon, from Spirit's perspective. In comparison, the rover Opportunity is currently producing about 600 watt-hours per Martian day on the other side of the planet, in a region called Meridiani Planum.
Now, Spirit will take a "lily-pad" approach to exploring Mars. To ensure its safety, it will move from one pre-designated safe haven - an area with a north-facing slope - to another.
Once the weather improves, Spirit will likely check out another so-called vesicular basaltic rock, similar to Esperanza. These rocks have large holes that were created by cavities of gas in molten lava, giving them a distinctive, sponge-like appearance. Esperanza was the first type of vesicular basalt ever examined on Mars.
The Spirit rover, constricted by power and the low Sun, has spent the past nine months in the same location at Low Ridge Haven (see Spirit to start digging the Martian dirt). Three weeks ago, it finally got to move around before being ordered to safety.
Spirit is also bogged down by a front wheel that will not turn.
The rovers were designed to last 90 days. To kick off their fourth year on the planet, they have been upgraded with new software to allow them to operate a little more independently from ground controllers.
The new software will allow them to build better maps of the landscape to help them steer clear of obstacles. They should also be able to track a target visually, recognising that it is the same object even when viewing it from different angles.
They will also be able to identify dust devils and clouds, so ground controllers will not have to sift through all of the images to identify such features.
Because of the power constraints, Spirit has not had a chance to test most of its new software, but it was able to autonomously detect water ice clouds at an altitude of between 10 and 15 kilometres.
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