On Mars, a rover named Spirit has gotten stuck in soft, alien soil. About two weeks ago, its wheels dug into the Martian soil, and the plucky rover became trapped.
Spirit has been roaming the red planet for more than five years, but its roving days could be over unless scientists and engineers back on Earth can figure out how to get the robot unstuck.
Part of the problem is that the Martian soil isn't like the dirt in your backyard.
"It's a light, fluffy material. It's kind of like flour, and so you can't get much traction in that," says John Callas of NASA's Jet Propulsion Laboratory in Pasadena, Calif., the project manager for Spirit and its twin rover, Opportunity.
Both of the rovers have gotten embedded in the Martian dunes before, he says, but this time it's trickier.
"Prior to this time," Callas says, "the worst embedding event for either rover was when Opportunity was caught in a dune, which we nicknamed 'purgatory dune.' " Opportunity eventually escaped from "purgatory," but Callas points out that it was a fully functioning, six-wheeled rover at that time.
This time, Spirit doesn't have six working wheels. The right front wheel has been broken for years, and the rover has limped along by driving backward, dragging the wheel. And now, another wheel has stopped turning. "There's some reason to suspect that a rock may be jammed in that wheel," Callas says.
It gets worse. Callas and his team also believe that Spirit may have dug so far down into the dirt that its little metal belly may be resting on some rocks.
This is a problem, Callas says, because as anyone who has ever driven an off-road vehicle on Earth knows, "if you get high-centered on a rock or a stump, you know that you're not getting traction on your wheels because the weight of the vehicle is now on the rock and not on the wheels, where you get your traction."
Callas and his team will try to take a picture of Spirit's wheels and underbelly using a camera on the rover's robotic arm that's really supposed to take microscopic photos of dirt. Opportunity was recently able to use this kind of camera to take a picture of its underbelly, so scientists are hopeful Spirit will be able to do the same.
NASA will also set up a special sandbox here on Earth to re-create the Martian landscape. Right now, they are working on re-creating the consistency of the soil on Mars, and then they'll stick an identical rover in the box to test possible ways of getting out.
These rescue plans will take weeks. And, Callas says, his team is emotionally attached to the rovers.
"You know, we talk to them each day. We interact with them, they're responsive to us, they exhibit personalities," Callas says. "When you discover that one of them is in trouble, then you become very worried, much like, you know, a person would become very worried about a dear relative if they suddenly became ill or were in a difficult situation."
If the Spirit rover remains entrenched in the soft Martian soil, that doesn't mean it's dead. It could still take pictures to send back to Earth and do other science that didn't require moving. But Spirit would not be a rover anymore.