According to the Free Spirit blog, NASA has added a second test rover to the project, where scientists are working on a way of freeing the stuck Mars Rover, Spirit. The rover is stuck in soft soil at a site called Troy. The researchers are trying to duplicate the conditions in a lab to help develop strategies that would get the rover unstuck. But simulating Mars on Earth isn't easy as JPL's John Callas explains:
There is no perfect Earth analog for Spirit's current situation. There's less gravity on Mars, little atmosphere, and no moisture in the soil where Spirit is. It is not anything like being stuck in sand or snow or mud on Earth. Plus, since the rover moves only about as fast as a tortoise, you cannot use momentum to help. No rocking back and forth as you might do on Earth."
To complicate matters there is a large pointy rock beneath Spirit. Any escape path has avoid putting the rover's center of gravity directly over the rock. Otherwise, Spirit might get free of the sand only to become stuck on the rock. For more, see our June update on Spirit's astronomy photos and panoramas of the area where it's stuck.