If you’re really desperate to escape the heat that’s blanketing North America, you might consider visiting Gusev Crater on Mars. It’s winter there, no problem with heat at all.

If you go, you’ll find a robot from Earth already there. The NASA rover called Spirit landed in Gusev Crater more than six years ago. Since then it has been snapping pictures and exploring the Red Planet’s watery past. Until recently, that is. Now the rover is silent. It’s in a kind of hibernation mode in order to survive the Martian winter. Almost every instrument, including the communication radio, is shut down.

Winter is always a tough time for a solar-powered outpost on Mars. Days are short, the sun is low on the horizon, and it’s cold. Really cold. More than 60 degrees below zero.

“That’s colder than the rover has ever been on Mars,” says John Callas, mission manager for NASA’s rover program at the Jet Propulsion Laboratory in Pasadena, Calif. “The rover was tested to that temperature here on the ground, but that was seven years ago with a brand new rover. This is a rover that is quite senior.”

And this was a mission that was intended to last 90 days, not seven years.

A Deep Sleep

In previous winters, the rover used battery powered heaters to keep warm. But this year, those heaters are shut off to save energy. There are two reasons for that. First: the rover’s been stuck in the sand for more than a year with its solar panels not pointing in the best direction. And second, those solar panels are covered with Martian dust, so they’re not as efficient at recharging the rover’s batteries. That’s why engineers let Spirit enter a deep sleep mode for the winter.

“When Spirit will wake up is very uncertain right now,” says Callas. It will only wake up when the days get longer and the solar panels are able to recharge the batteries. Callas says a computer model predicts the rover might wake up sometime around the late September/early October time frame. But Callas says the model’s calculations are based on several assumptions, so it may not be very accurate.

“The rover could wake up tomorrow if temperatures are warmer than we expected,” he says. “That’s why we’ve been listening [for a signal] every day.”

Even if it does wake up, its roving days are likely over. Two of its 6 motorized wheels have stopped working, and mission managers are not optimistic about getting it rolling again. But Callas says if Spirit does wake up, it still makes a great weather station, and can help with experiments designed to understand the planet’s core.

‘Opportunity’ Rolls On

On the other side of Mars, Spirit’s twin rover, Opportunity, is in much better shape. It also uses solar arrays for power, and it also has lots of dust on those arrays. But every once in a while, Opportunity gets lucky.

“Recently, we had a cleaning event on Opportunity,” says Callas. “Part of the dust on the solar arrays was blown off by some sort of wind event, and now we have a lot more power, and we can drive almost every day at this point.”

Opportunity is on its way to a large crater called Endeavor. Scientists hope to find very old rock formations there. Opportunity started its 12-mile trek to the crater two years ago, and it’s about halfway there.

Some of the instruments on Opportunity are showing signs of age, but Callas won’t make any predictions about when its mission will end.

“We’re going to keep going until the rover stops,” says Callas.

And at least for now, that day still seems a long way off. Copyright 2010 National Public Radio. To see more, visit http://www.npr.org/.