What a difference a couple of months of driving make. Here's the sort of view of the Mars Exploration Rover Opportunity's road ahead that I'm accustomed to, taken two months ago. Dune after dune after dune stretching to the horizon, with only a couple of spots of lighter bedrock here and there breaking up the monotony. The rim of Endeavour crater, about 9 kilometers away, is the dark smudge just above the horizon.
Well, that view is finally changing, more or less for good. There are still plenty of dunes left for Opportunity to cross, but they are getting smaller and smaller, and yielding to larger and larger patches of bedrock.
This is very, very good for driving, for one reason that's easy to guess and one that you might not appreciate. One reason is simply that bedrock makes for easier driving than soft dunes, just as it's easier to walk across a parking lot than a dry, sandy beach. But there's another reason Opportunity will be able to drive faster as the dunes give way. Opportunity does some driving under very specific commands from Earth, for as far as her drivers can see in her images. Once she rolls past the horizon of her images, she can extend a day's drive under her own control. When she's driving autonomously, she has software that uses her camera images to investigate the landscape in front of her for hazards. That software can have a tough time with the repetitive sand dunes, because it can be difficult for Opportunity to figure out which dune is which in her images, and thus measure how far she has traveled, or how far she can safely go. But this bedrock with disconnected dunes will be much, much easier for her software to understand, leading to longer autonomous drives.
For most of the year, Opportunity has been averaging around 70 meters of distance per driving day (with roughly three driving days per week). Over the last month, that number has been increasing, to 80 meters, and then 100 meters with her new ability to autonomously drive backwards. On this new rocky terrain, rover driver Scott Maxwell says we can probably anticipate 140 meters per driving day. Doubling her traverse rate sounds good to me. Keep on rolling, Opportunity!