NASA's beleaguered Mars rover Spirit may no longer be much of a rover, but it's not the end of the road for her yet. The semi-stuck robot still has plenty of science left to do on the red planet, mission scientists say.
"There's actually a whole class of scientific objectives that you can only address from a vehicle that doesn't move. So far we've pretty much tended to ignore those," said rover mission principal investigator Steven Squyres of Cornell University in Ithaca, New York.
Squyres and other mission mangers announced last week that they were halting the effort to free Spirit from the sand trap it has been stuck in since May and shifting efforts to preparing the rover for the upcoming Martian winter.
The rover's handlers will try over the next week to position the rover to maximize the amount of solar radiation it receives to give it the best chance of making it through the winter.
"Energy is getting so low that we think we only have, you know, at maximum another half-dozen drives to be able to do that before we have to hunker down and get through the winter campaign," said science team member Ray Arvidson of the Washington University in St. Louis.
That winter campaign won't see the rover doing much: "In the dead of winter, it can try to survive, that's about it," Arvidson told SPACE.com.
From now until the Martian winter solstice in May, the vehicle will wake up during the day and if it thinks it has enough energy, it will wait for a signal from Earth. If it has a bit more energy, it will take some atmospheric measurements and do some radio science.
Spirit is equipped with an X-band transmitter and receiver on its high-gain antenna that can find the Deep Space Network and establish communication over about 20 to 30 minutes. Doppler tracking of the rover's signal can "very, very accurately locate the rover." Those measurements added up over six months could be used to locate the precession, or wobble, of Mars' spin axis.
Small variations in the precession can in part be driven by the properties of a planet's core, such how big it is or whether it is liquid or solid.
"So this could provide major new information about the interior," Arvidson said.
A rover wouldn't be able to do this kind of science because it would constantly change position, so a stationary target is needed, Squyres noted. Spirit's predicament provides the perfect opportunity to do this kind of science, Arvidson said.
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Spirit will also operate a weather station while it's stuck in place.
The rover and its twin Opportunity have been exploring different parts of Mars since January 2004 and far outlasted their initial 90-day missions. Both rovers are now in their seventh year of Mars exploration.
If Spirit makes it through the winter, the next objective will be to see if it can find any more of the intriguing layered soil it inadvertently found when it got stuck.
Over the past few months, scientists have had ample time to investigate the unusual feature that Spirit was mired in and it has turned out to be one of the most geologically interesting places the rover has visited in its six years on the red planet.
The compounds that Spirit has found in these layered soils indicates that the site periodically becomes slightly wet, with some chemicals dissolving into the water and others being corroded by it. Arvidson says this is likely the result of snow packs being periodically deposited on the site when Mars is at a higher degree of tilt with respect to the sun.
What scientists want to know now is whether or not this spot is unique, or whether this layering is a more widespread feature.
If the team can pop Spirit out of its current spot (and it has moved backward by about 20 centimeters over the last week, Arvidson noted), it might be able to drive to the center of the crater it has been stuck in, or features a few meters to the north or south of the crater.
More long-range driving is out of the question, because even if it is freed, Spirit will still only be a 4-wheel-drive vehicle – good if you're climbing mountains on Earth, but not if you're a Mars rover. The rover has six wheels, like its robotic twin Opportunity, but two of its wheels are broken.
"With four-wheel drive in this pretty dicey area, we're not going to go very far," Arvidson said.
Arvidson already has a few sites in mind to check out once spring rolls around.
With the backwards motions done over the past week, "we already have newly exposed soils," Arvidson said. So even though Spirit will rove no more, "there's still a lot to do," he added.
How much Spirit will be able to do in this new phase of the rover mission isn't known; even mission managers don't know how long the hobbled robot will last.
"Are we going to have an eighth year?" Arvidson asked.
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