BOULDER, Colo. – NASA’s indefatigable Mars Exploration Rovers (MER), which are marking their third anniversary on the red planet this month, got new software over the last several weeks that will allow them to recognize certain features and keep visual tabs on the surrounding terrain as they move across the surface with more autonomy than ever before. The new software gives the rovers the freedom to decide when it is safe to reach out with their instrument laden arms to touch rocks or other interesting targets.

“Before this, the rovers could only think one step ahead about getting around an obstacle,” John Callas, NASA’s Jet Propulsion Laboratory’s project manager for the rover mission, said in a statement. “With this new capability, the rovers will be smarter about navigating in complex terrain, thinking several steps ahead. It could back out of a dead-end cul-de-sac. It could even find its way through a maze.”

The rover Spirit touched down first, landing inside Gusev Crater Jan. 3, 2004. Twenty-one days later Opportunity landed on the other side of Mars, touching down in a region known as the Meridiani Planum. Several mission extensions later, Spirit and Opportunity continue their trek long after surpassing their minimum 90-martian-day missions.

To date, NASA has set aside about $922 million on the Spirit and Opportunity missions, which includes their initial $820 million price tag plus several additional mission extensions beyond the initial plan for 90-days of operations, the space agency said in a Dec. 28 press release.

Spirit: back to Home Plate

So far Spirit has captured some 88,500 photographs, scaled one hill, and rolled across 6.9 kilometers of rocky terrain. Scientists are preparing to steer Spirit back to a region at Gusev Crater called Home Plate – a still baffling formation near the region of Mars known as the Columbia Hills.

The plan is to take Spirit back to the edge of Home Plate and then pick up where it left off last martian fall, continuing a drive clockwise around its south edge, said Larry Crumpler, a MER science team member based at the New Mexico Museum of Natural History and Science in Albuquerque.

Another goal will be to see if there are any indicators of Home Plate’s geologic origin – be it volcanic or just a product of wind action.

“Although it is clear that the materials that make up the outcrops are volcanic, it is not clear whether the deposition was volcanic in origin – air fall or ballistic – or whether it was just blown into a low spot by normal wind processes,” Crumpler said.

This is probably the first place where real field geology has come to the fore, he said. “Chemical analysis of the rocks can tell us many things, but it can’t tell you in every case how the rocks got where they are … that’s the job of field geology,” Crumpler said.

Beyond Home Plate

“We should begin exploring the unseen southern margin of Home Plate in the new year,” said Jim Rice, a science team member of the Mars Exploration Rover Project at Arizona State University in Tempe.

“I am personally looking forward to seeing new cross sectional views of the layered rock outcrops along the southern margins of Home Plate,” he said. “How long we will stay at Home Plate is unknown … it sort of depends on what we find there. This is the nature of exploration.”

After Home Plate, Rice is hoping to study features nicknamed von Braun and Goddard, after the two great rocket pioneers.

“These are very high-priority targets in my opinion,” Rice said. “Von Braun looks like some of the classic layered buttes and mesas one would see here in Arizona. Goddard could be either an impact crater or volcanic vent. The only way to know is to go.”

How these two features fit into the overall, complex story of the Columbia Hills has yet to be determined, Rice said, adding that he is longing for a look at another big target labeled the Promised Land, a region named some three years ago shortly after Spirit landed.

The origin of this material is unknown, and this region would in effect constitute a new landing site, Rice said.

The start of the Promised Land is about 800 meters away – a long haul given Spirit’s mobility issues. The rover’s front right wheel is not working properly, so the robot is dragging it, while using its five other wheels to move about.

“It makes approaches for studies of targets with the instruments tricky, requiring a crab-like motion to put targets within the instrument work space,” Crumpler said . “So the first drives are tentative and very carefully considered for their value in learning anew how to drive on Mars.”

But Rice said that should not stop scientists from trying to reach Promised Land. “It would be a shame if we only see it from afar. We will not know what possible geologic treasures the Promised Land holds until we enter its domain,” he said.

Target Rich Environment

Most recently, Spirit has been busy looking at a target dubbed Esperanza – the first vesicular basalt that has undergone detailed scrutiny. Vesicular basalts form when dissolved gas in lava comes out of solution “like bubbles in soda,” creating little Swiss-cheese-like voids within the rock, said Steve Squyres, lead scientist of the Mars Exploration Rover project from Cornell University in Ithaca, N. Y.

“We’ve seen lots of vesicular basalts at Gusev, particularly around Home Plate, and this is our first chance to really find out what they are made of and how they may or may not be related to Home Plate,” he said.

Squyres said Spirit is likely to stay in the vicinity of Home Plate for a long time.

From overhead, NASA’s Mars Reconnaissance Orbiter has used its High Resolution Imaging Science Experiment (HiRISE) camera to image the site that Spirit is now appraising.

“The recent HiRISE image of the Spirit site has shown us that there are many more scientifically interesting targets around Home Plate than we realized. Some of these features are difficult to spot from ground level,” Squyres said.

The powerful HiRISE camera has found things that Mars rover scientists had not realized were there before. “So, having found our way with much difficulty to such a target-rich environment, we’re going to work it for all it’s worth.”

Exploring Victoria Crater On the other side of the planet, Opportunity is continuing with its scenic tour of the rim of Victoria Crater, said William Farrand, a research scientist at the Space Science Institute in Boulder and a member of the Mars Exploration Rover science team. The next priority for scientists is to find an acceptable path to steer Opportunity into Victoria Crater.

“So far we have found two safe entry routes into Victoria. Those are Duck Bay and Bottomless Bay. We have not yet confirmed that either is a safe exit route, but they both have potential,” Squyres said.

“We have been getting some spectacular panoramas of the promontories and inner rim of Victoria. We are also in the process of building up images for a fabulous stereo model of the crater,” Farrand said.

It is still a bit early for rover science team members to assess the entire geologic story contained in the walls of Victoria Crater, Farrand said. Doing so calls for detailed inspection of the stratigraphy of the walls, or an assessment of its strata, or layers.

“We are really taking a methodical approach to mapping out the stratigraphy exposed in the walls of the crater. Once we’ve gotten further around, I think we will have a better understanding of what that stratigraphy is telling us,” he said.

Within Meridiani Planum, the Opportunity rover has been relaying pictures of Victoria Crater and its walls, Squyres said. So far, the story at Victoria is surprisingly similar to what rover scientists saw at Endurance Crater, which they closely studied for months in 2004.

Squyres said the rover’s Panoramic Camera has revealed that the rocks in the crater are mostly “fossilized dunes” – with layering that preserves clear evidence of ancient transport by wind.

Opportunity‘s Mini-Thermal Emission Spectrometer (Mini-TES) has revealed that this material is sulfate-rich all the way down, Squyres said. Mini-TES characterizes the martian terrain by using thermal infrared spectroscopy.

“So the picture we got back at Endurance, with a sulfate-rich dune field and signs of acidic groundwater, seems to apply here as well … several kilometers to the south,” Squyres added. “This was a big, long-lived dune field and there was lots of water here.”

Leonard David has been reporting on space activities for nearly 50 years. He is the 2010 winner of the prestigious National Space Club Press Award and recently co-authored with Apollo 11’s Buzz Aldrin the book “Mission to Mars — My Vision for Space...