So the Mars rover Opportunity got a bit too wild while driving recently and got stuck in a sand dune. On Earth, we know that rocking back and forth is a good way to get un-stuck, and if all else fails, call AAA. But on Mars, and when talking about a multi-million-dollar robotic laboratory, rocking is not an option, and AAA will take too long to get there. So the Mars rover team had to do some tests to find a way out of the sand dune.
Due to some smart thinking, the team has a duplicate rover here on Earth. So they spent a couple weeks meticulously reproducing a Martian sand dune. Since we don't have any Martian sand, the scientists had to use close-up pictures of the sand taken by the rover and then mix up a similar-looking concoction here on Earth. They ended up using a mixture of sand, clay, and diatomaceous earth (dirt made of tiny shells from microscopic plants). After testing with the Earth-based rover, the scientists then were able to send instructions to Opportunity to begin moving out, a few inches at a time.
As of right now, this method seems to be working! In a few more days, Opportunity should be prowling the Red Planet once more. I bet you that the Earth-based drivers are a bit more careful to avoid dunes in the future, though!
You can read more of the ongoing adventures of the Mars rovers Spirit and Opportunity at NASA's Mars Exploration Rover Homepage, which also includes lots of cool pictures the rovers have been taking. Be sure to have 3D glasses (the kind with red and blue lenses) so you can see what Mars looks like in three dimensions!