Not sure if the rover itself has a VM but the ground control software is:
http://news.com.com/2100-1007_3-5142220.html?tag=nefd_top My lego mindstorm (32k) can be flashed to use a Java VM and the JavaCard technology is ultra low footprint as well. There are a few cell phones that run a VM and I can think of a few other devices that use Java as well.