NASA's oldest rover, Opportunity, emerges from another Martian winter in good shape

The view from Opportunity Rover on Mars.

 Let's celebrate, because Opportunity, NASA's oldest Mars rover, has lasted through another harsh winter on the Red Planet.

Like Earth, Mars has a tilted axis. But because Mars takes longer to circle the sun, its seasons are nearly twice as long.

With the sun hanging low and appearing only for a brief time each day, keeping Opportunity charged via its solar panels is a challenge. Engineers worried the rover wouldn't make it through its first winter on Mars. But this week, the rover emerged on the other side of the season's shortest-daylight weeks.

"Opportunity has made it through the worst part of its eighth Martian winter," Jennifer Herman, power subsystem operations team lead for Opportunity at NASA's Jet Propulsion Laboratory, said in a news release.

To keep Opportunity charged and rolling through the fall and winter in Mars' southern hemisphere, engineers tilt its solar arrays northward toward the equator.

The rover is currently exploring Perseverance Valley, a region carved by ancient liquid flows. Scientists have plotted a course through the valley that allows the rover to stop and study at north-facing sites, allowing the rover to power-up as it carries out its scientific duties.

But winter time isn't the only threat.  Dust storms that cover the solar array with crud are also a big worry.

Some planetary scientists think Mars is due for another big dust storm in the southern hemisphere in the spring of 2018.

"If Opportunity's solar arrays keep getting cleaned as they have recently, she'll be in a good position to survive a major dust storm," Herman said. "It's been more than 10 Earth years since the last one and we need to be vigilant."