In monitoring the progress of Opportunity, Dr. Joy Crisp, Project Scientist, reported that the Mars science group so far is "thrilled with the match" between their predicted models for the martian atmosphere and what Spirit actually went through during its descent last Saturday. Those same models will be used when the second rover, Opportunity, tries to land in less than two weeks.

"That atmospheric reconstruction is complete," Crisp said, "and only for the fourth time in history do we have a temperature versus height plot for Mars. This is a measurement taken thousands of times every day on Earth, with atmospheric sounding balloons, but it gives us confidence for the next rover's landing" to know the models match well with what Spirit recorded.

Since these models for the martian atmosphere panned out, there are currently no plans to change Opportunity's entry significantly. A nine-second planned thruster burn was initiated on Friday, in a trajectory correction to put Opportunity closer to its final aim point in a region on Mars thought to be rich in aqueous minerals called hematite.

Meridiani is likely to have a more grey, volcanic look to it than Gusev's flat plain, but with intriguing possibilities for also having a water-formed history and an aqueous mineral called hematite. The rock density at Meridiani is also hoped to be less than twenty percent of the landscape, which will make driving longer distances possible.

Matt Golombek, project scientist for the 1997 Pathfinder mission and a current Spirit science team member previewed what those initial panoramas from Meridiani might appear like: "It will look completely different. Meridiani has virtually no dust (low albedo). You will see a dark-grey basaltic plain, with much more of the rolling landscape" seen by Pathfinder.

The anticipated Mars landing on Jan. 24 of the Opportunity rover will be a bit more challenging than the Spirit's bounce onto the red planet earlier this month, according to a University at Buffalo geologist, but if it's successful, then scientists will be able to be much bolder about selecting future Mars landing sites.

"If both of these landers survive with airbag technology, then it blows the doors wide open for future Mars landing sites with far more interesting terrain," said Tracy Gregg, Ph.D., University at Buffalo assistant professor of geology in the UB College of Arts and Sciences and a planetary volcanologist.

Gregg, who headed a national conference at UB in 1999 regarding the selection of future Mars landing sites, is chair of the geologic mapping standards committee of the NASA Planetary Cartography Working Group.

"With the success of Spirit, I feel so much more confident about future Mars landers," said Gregg. "The airbags seem to be able to withstand quite a bit of trauma."

Gregg remembers attending a conference presentation a few years ago by Matt Golombek at the Jet Propulsion Laboratory in which he proposed the airbag landing technology.

"He listed the 15 steps that had to happen at exactly the right time and in exactly the right way in order for this technology to work. The general mood in the lecture hall was, 'Yeah, right, good luck,'" Gregg remembered. "Well, the next year, he got up to a standing-room-only crowd at a meeting of the same organization and he described all of the same steps that the Pathfinder had successfully completed on Mars. He got a standing ovation."

The selection of Mars landing sites is a complex balancing act, Gregg says, where the potential for important scientific discoveries has to be balanced against the requirement that sites be absolutely safe so that the rovers can perform well and send data back to earth.

Both Gusev Crater, where the Spirit landed, and Sinus Meridiani, where Opportunity is scheduled to land, were chosen, Gregg says, because they are not expected to have large boulders, steep cliffs or deep craters that could pop an airbag or swallow up the lander preventing the transmission of radio signals.

"If Opportunity survives the landing on Jan. 24, there is a high possibility that we will get to see layers of ancient rock, deposited when Mars was warm and wet and could have supported life," she says. "Evidence of river channels, which we expect to see at Sinus Meridiani, could be remnants of that early, warm history."

When pictures start coming back from Opportunity, Gregg will have her eyes peeled, searching for layers in the walls of the dried-up river channels.

"Those layers could be lava flows," explained Gregg, noting that often the best place to look for evidence of life on any planet is near volcanoes.

"That may sound counterintuitive, but think about Yellowstone National Park, which really is nothing but a huge volcano," she says. "Even when the weather in Wyoming is 20 below zero, all the geysers, which are fed by volcanic heat, are swarming with bacteria and all kinds of happy little things cruising around in the water.

"So, since we think that the necessary ingredients for life on earth were water and heat, we are looking for the same things on Mars, and while we definitely have evidence of water there, we still are looking for a source of heat."

Gregg hopes that a future landing Mars site will be near a volcano, particularly one called Apollinaris Patera.

"A landing site near a volcano might be possible, now that the airbag technology has worked so wonderfully," she says.

What's Next
Arizona planetary scientist, Dr. Bill Hartmann, is a member of the Mars Global Surveyor imaging team that is monitoring both landing sites from orbit. Hartmann, if forced to choose, said Opportunity's site, Meridiani, offers both challenges and rewards unlike Spirit's Gusev landing site. "My favorite is Terra Meridiani, because hematite mineral concentrations are detected there, possibly due to hydrothermal activity, and our crater studies (with Dr. Melissa Lane in our group) suggest a very old surface (a lakebed?) That was only recently exhumed".

"A problem I see for all ... landing exploration plans is that, in general, Noachian lakebeds will not be well preserved", said Hartmann. "Mars is cratered down to sizes of a few meters or less, and according to a recent paper of mine, impact gardening will chew up the surfaces in less than one billion years. So...you can't pick out Noachian lakebeds and expect them to be intact at the exploration scale of 1-10 meters (~3 to 30 feet)".

Hartmann concluded: "That's why I like Terra Meridiani, where we may get lucky and see a surface that has been covered, preserved, and then exposed by exhumation only a few million years ago".

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