The Mars Exploration Rover Spirit has pulled off the unthinkable by ascending to the summit of a Martian hilltop, a breathtaking perch where the never-say-die craft has captured an inspiring panorama of the surrounding vistas and given Earth-bound geologists a window in the area's ancient past.

Spirit's panorama from the top of Husband Hill. Credit: NASA/JPL-Caltech/Cornell Download medium | very large image

When the tiny rover left Earth 27 months ago, scientists could hardly dream Spirit would still be alive and well in the summer of 2005, let alone becoming a successful mountain-climbing machine. But Spirit has done all of that.

Giddy officials and scientists gathered at NASA Headquarters in Washington on Thursday, the 591st day of Spirit's planned 90-day mission roving the surface, to unveil the sweeping panorama that the vehicle has taken from atop Husband Hill.

"We have taken a beautiful 360-degree panorama, which I believe is going to be truly one of the signature accomplishments of this mission," said Steve Squyres, the rover principal investigator from Cornell University.

Robotic detectives

Spirit was sent to Gusev Crater, a vast 100-mile wide bowl suspected of once harboring a lake, where scientists believed evidence of past water could be uncovered. Meanwhile, sister rover Opportunity was dispatched to Meridiani Planum, a region half-a-world away coated with the mineral gray hematite, which typically forms in watery conditions. Proving Mars was once wet is key in the search for past life on Earth's neighboring planet.


Additional coverage for subscribers:
VIDEO: SPIRIT'S PANORAMA PRESENTED WITH EXPERT NARRATION PLAY
VIDEO: ROVER DRIVER DESCRIBES GUIDING SPIRIT UP THE HILL PLAY
VIDEO: A LOOK AT SPIRIT'S RECENT SCIENCE ACTIVITIES PLAY
VIDEO: OPPORTUNITY ROVER'S LATEST SCIENCE FINDINGS PLAY
VIDEO: CURRENT HEALTH STATUS OF BOTH ROVERS PLAY
VIDEO: THURSDAY'S NEWS BRIEFING DIAL-UP | BROADBAND 1 & 2
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By complete luck, Opportunity's airbag-cushioned arrival on the planet ended with the craft rolling into a tiny crater. When the rover unfolded from its descent cocoon and opened its eyes, exposed bedrock that Opportunity later used to confirm Mars indeed had a wet history was within reach from the landing pad.

Spirit, meanwhile, was sidelined by serious computer ills and then found a landscape devoid of the watery proof scientists so eagerly sought.

Gazing eastward across the plains of Gusev from Spirit's landing site was a range of seven hills, named the Columbia Hills in honor of the lost space shuttle astronauts. Situated one-and-a-half miles away, it seemed unlikely the rover could drive that lengthy distance before succumbing to the harsh Martian environment. But the long drive began with ambitious hopes of making it.

"When we first touched down at Gusev Crater on the night of January 4, 2004, the Columbia Hills seemed impossibly far away. It was a necessary place for us to get to, though, because as we looked across the plains we quickly realized these plains were made of basaltic lava. This was stuff that was interesting but did not tell us what we really sought to know about Gusev Crater, and that is whether there had been water here. So in order to find something, in order to find something different, we had to make that mile-and-a-half drive," said Squyres.

An image taken by Spirit's PanCam from the rover's landing site looking west depicts the hills dedicated to the Columbia crew. Credit: NASA/JPL/Cornell

Spirit has spent the past year climbing Husband Hill, named for Columbia commander Rick Husband. The vehicle's upward trip was been slow, with numerous pauses along the way up to examine soil and rocks with its instruments and collecting clues that actually do show water has been in Gusev Crater.

"We're finding abundant evidence for alteration of rocks in a water environment," said Ray Arvidson of Washington University, the deputy principal investigator for the rovers' science instruments. "What we want to do is figure out which layers were on top of which other layers. To do that it has been helpful to keep climbing for good views of how the layers are tilted to varying degrees. Understanding the sequence of layers is equivalent to having a deep drill core from drilling beneath the plains."

What's more, the rocks Spirit has encountered in the hills are much older than those in the plains, creating a window into the very ancient past, Squyres said.

"They provide a wonderful glimpse into what Mars was like in the earliest part of its history. It was a violent place. It was a place where meteorite impacts were happening frequently. It was a place where there were volcanic explosions happening frequently, hot stuff was raining from the skies. There was water. When rocks were deposited, water would flow through those rocks (and) change their chemistry.

"How variable that was around the planet? Don't know. We've only been to two places with these rovers. But what it does is it tells us Mars was dramatically different at the time when these rocks were formed than it is today."

Spirit: Mars mountaineer

At 270 feet tall, Husband Hill is roughly the Statue of Liberty's height.

"That's no Mount Everest, but for a little rover this is a heck of a climb," said Squyres.

The Mars Exploration Rovers were not expected to climb steep hills, but controllers at the Jet Propulsion Laboratory were able to learn how to manage Spirit and drive the six-wheel vehicle up the incline.

"It has been a great adventure to get onto the summit of this hill. I know we went there for science reasons but nonetheless (for) the people that drive the rover every day it's been a journey of exploration," said Chris Leger, one of the rover controllers.

"Every day that we come in and drive we see images that came down (to Earth). It's a new vista, something that people have never seen before. After doing that for 591 sols, you really get the feeling that you're on Mars yourself."

This perspective view of a three-dimensional model shows the route NASA's Spirit rover took to the top of "Husband Hill," and the shape of the surrounding terrain. This map is made up of images taken by the Mars Orbiter Camera on NASA's Mars Global Surveyor and processed into a three-dimensional terrain model by the U.S. Geological Survey. Credit: NASA/JPL/USGS/MSSS Download larger image here.

The decision to attempt ascending Husband Hill stemmed from three main reasons, Squyres recalls.

"The British mountaineer George Mallory was once famously asked why he was trying to climb Mount Everest and his famous reply was 'because it is there.' That's a compelling argument when you are a mountaineer. But for an $850 million rover mission you better have a better reason than that," Squyres said.

• The search for new geologic material led the researchers to the hills.

  "When you want to explore the diversity of layered rocks, if you want to go up through the stack, you need to go uphill," he said.
  
  

• Increase the amount of solar power available to the rover as Martian summer faded into winter during the rover's extended life.

  "We actually used the topography to tilt the entire vehicle and tilt the solar arrays towards the sun. In the southern hemisphere in the winter, the sun is low in the northern sky. So in the wintertime we operated on north-facing slopes."
  
  

• Use the summit as an observation platform.

  "When you go to the summit of a hill you get very good visibility into and access to new terrain. We've known for a long time that the next place we want to go after Husband Hill is the terrain to the south. We have pictures taken from orbit that tell us there's some interesting geology down there, but (the pictures) are not good enough to really plan our route, they are not good enough to plan our targets. What field geologists typically do, and Spirit is a robotic field geologist, is you'll climb to the nearest hill just to take a look around, get the lay of the land and figure out where you want to go next. And that is exactly what we have done with Spirit."

But driving up the hillside was not easy.

"Chris will remember vividly as we were struggling along the northwestern flank of that mountain how much loose, fine-grain stuff there was. Our wheels would dig in, we'd slip around and we'd dig in deep. Remember that potato-sized rock we got stuck in the wheel once? It was really treacherous driving because there was accumulated dust there. We were probably in the wind shadow on the lee side of the hills at that point," said Squyres.

The exposure of the terrain to the wind has a profound impact on conditions, as Spirit experienced along the way.

"What we have found once we've gotten up into the summit region...the driving has gotten very, very good. The ground is hard here. There is not a lot of fine-grain stuff around. What there is piled up in drifts. This is because the summit region is exposed to the wind; it's very windy. In some parts of the summit region, we barely leave tracks," Squyres said.

Future ambitions

The rover team is "wrestling" with the question of how long Spirit will remain on the hilltop doing science investigations on rock targets before proceeding onward, Squyres said, but the vehicle is expected to remain up there for at least a few more weeks. Spirit's exit route will be down the southern slope of Husband Hill.

A view to the possible areas Spirit will explore next once leaving Husband Hill. Credit: NASA/JPL-Caltech/Cornell

"With respect to how long it's going to take us to get down the hill, we don't have a whole lot of experience driving this vehicle downhill -- we've been going uphill for more than a year now," Squyres said. "We're going to have to take it carefully at first and learn as we go. I think the deciding factor is going to be how good the geology is. If we're finding geology that offers truly compelling targets (for study) as we found on the way up, then our pace is going to be a lot slower whereas if it's a lot of loose sand and that sort of thing we'll be able to move through it a lot more briskly and head to the good stuff off in the distance."

"We're curious to see whether or not the rocks, in fact, are tilted to the south," Arvidson said of the descent. "So far, we have seen them largely tilted to the north. That is going to tell us about the structure and a little bit more about the evolution of the Columbia Hills. And also whether or not the variety of the rocks that we've seen so far continues to increase."

One future destination is a mysterious spot south of the hill dubbed "Home Plate" that appears to be a flat plateau with a bright perimeter.

Also being targeted by scientists is an area of unsettled terrain, if the rover can manage to drive through the landscape.

"That very rugged stuff. There is a guy on our team who actually calls this the geologic promised land. I don't know if it's going to turn out to be that good or not and I don't know if we'll ever get there, but it certainly looks interesting," Squyres said.

Both Spirit and Opportunity are budgeted to operate through September 2006, if either robot survives that long.

"As long as the vehicles remain healthy and they continue the science return, we'll do what we need to do to keep them operating and learning. An asset on the surface like this is invaluable, and we certainly wouldn't want to prematurely cut them off," said Doug McCuistion, NASA's Mars exploration program director.

"Both rovers continue to be in superb health. It has been just a remarkable mission and I would say we literally feel on top of the world right now being on the summit of Husband Hill," Squyres said.