Rock fragmentation at rover site possibly result of water
Posted: January 12, 2004

The first 360-degree panorama taken by the Spirit rover's main camera system provides a spectacular view of Gusev Crater's cracked and churned-up floor, including an abundance of small, cracked rocks and fragments that could be the result of water-driven erosion in the distant past, researchers said today.

The 360-degree pan from Spirit. Credit: NASA/JPL/Cornell
Download a large version here.

The long-awaited panorama was made up of 225 frames in three colors that were shot over three days on the martian surface. The individual frames were digitally stitched together to form a riveting mosaic.

"This is a 360-degree view," said Michael Malin, a Spirit science team member and president of Malin Space Science Systems. "This is multiple thousands of pixels high and many tens of thousands of pixels wide. In fact, being shown here is something that we assembled at one half the resolution and one quarter the number of pixels because the sheer number of pixels was slowing down our machine in getting it ready for you today. We felt it as better to get it out and we'll show you a little later on, maybe in the next couple of days, a better view of it. This view in itself will jam any download you ever tried to perform.

"The whole panorama is there before us," he said. "It's a great opening to the next stage of our mission, which is to get off the rover and start moving out into this field."

Malin said the fully assembled panorama will help researchers get a "feel" for Spirit's landing site that will pay dividends as the rover's mission finally gets underway.

"Seeing the panorama totally assembled as opposed to individual pieces gives you a much greater appreciation of the relative position of things," he said. "It begins to help us develop a sense of direction. North, south, east, west are concepts until you actually have features you can see and I find it easier to be able to visualize where I am on Mars when I can look in one view at all those different directions.

"We're also working on trying to come up with ways of better viewing this. In the old days, during Surveyor, we actually took the panoramas that we made, stuck them on the insides of spheres and then stuck our heads up into the spheres. You laugh, but it gave you a very, very intense sense of being there. And I'm trying to figure out a way of doing something not unlike that with this pan. Because it is at truly remarkable resolution, you know, eye-ball visually appealing. For a field geologist, it's exactly the type of thing you'd want to look at and gain an understanding of where you are."

Kevin Burke, an engineer at the Jet Propulsion Laboratory in Pasadena, Calif., said Spirit's much-anticipated move from its lander to the martian surface remains on track for early Thursday morning East Coast time. "We're about to kick the baby bird from the nest," he said.

Overnight Sunday, engineers used a ground version of Spirit to verify the maneuvers designed to get the rover off its lander will, in fact, work. No problems were found and starting tonight, Spirit will begin a two-phase operation to rotate in place on its lander, slowly spinning 115 degrees to its right, to line up with the desired egress ramp.

First, Spirit's computer will send commands to fire an explosive guillotine, severing a final bundle of electrical cables connecting the rover to the lander. Assuming no problems are found, Spirit will be commanded to back up 9.8 inches "to get our rover centered on the deck obstacles we're going to be spinning over the top of," Burke said.

The computer then will command the four wheels on the four corners of the rover's rocker-bogey suspension to "toe inward" 45 degrees.

"That is going to let us know that all of the mobility actuators are functional," Burke said. "That's going to make our mobility engineers very excited, because we have four actuators that as of yet, we don't know if they work or not."

The 115-degree turn in place will be done in stages, with the first 45-degree move planned early Tuesday.

"The reason we're going there is to assess a blind spot that we cannot see," Burke said. "The solar arrays, the right-hand side, the solar arrays cover up a spot on the soil that we have no knowledge of at this moment. The 45-degree turn in place is a safe move that allows us to turn back forward if we find something there that we don't like. It also allows us to assess the mobility performance of the actual drive actuators.

"The next day (Wednesday morning EST), we're going to do the remaining two turn-in-places. We do a turn-in-place No. 2, which is a step from 45 degrees to 95 degrees. At the end of that maneuver, there's a stopping point where we're able to make sure we're in the right spot on the lander deck to continue on to get to the final position for egress. It's also the best position we're going to be in to adjust the rover position on the deck if we need to do so prior to reaching our final position.

"Then that same day is going to be a turn in place from 95 to 115 (degrees), which is our final egress angle," Burke said. "Then, the very next day (Thursday morning EST), we're going to be driving straight ahead at 115 degrees angle off the deck. That's going to put our rear wheels approximately one meter away from the ramp on the martian soil."

Spirit likely will remain in its initial position for quite some time while scientists use its instruments to study soil and rocks in the immediate vicinity. Researchers are particularly interested in probing soil churned up by the deflation and retraction of the lander's airbags. The soil has the appearance of mud and while no one believes liquid water is the cause, some sort of cohesive material, or force, must be at work to explain the soil's appearance.

Researchers call the patch of airbag-worn soil the "magic carpet."

A three-dimensional color model created using data from Spirit shows images of airbag drag marks on the martian surface. Credit: NASA/JPL/Cornell
Download a large version here.

"You can see a patch where the soil detached and was removed" as an airbag retracted, said John Grotzinger, a geologist at MIT and a member of the Spirit science team. "And that piece then advanced forward and formed this curl-up structure. What's so fascinating about this is that it doesn't exhibit the brittle deformation exclusively that we saw at Pathfinder and Viking (landing sites) but instead, we also see a more ductile, plastic form of deformation in that feature. So this is really exciting and the science team looks forward to working on this problem."

On a more global level, Malin said the rocks in the vicinity of Spirit's landing site are smaller and more fragmented than those seen at the Mars Pathfinder and Viking landing sites.

"My work in Antarctica has led me to lots of rocks that have been split by freeze, thaw and other physical weathering phenomena, almost all of which require water in a liquid state," he said. "The fact that I see more fractured, cracked rocks at this site than I see in all the other sites combined, to me suggests that at some time in the history of this surface, water was involved in the physical breakdown of the rocks."

But other explanations are possible, he said. Some researchers believe shattering impact events could have produced the tortured terrain seen today. Either way, "there are things we can look for when we go over to the rocks that will let us decide between those models," Malin said.

Water, of course, is the central theme in NASA's Mars exploration program. Spirit and the identical rover Opportunity, bound for the other side of Mars, were built to find out how long the water that once carved the red planet's surface persisted. If it was present for long periods of time, life might have had a chance to evolve.

Gusev Crater is believed to have once held a vast lake. But the surface seen by Spirit bears little resemblance to a dry lakebed. It's likely the crater floor has been shaped by a variety of processes occurring over time, including the effects of water, impacts and, possibly, volcanism.

Looking across the landing site, "the topography is rolling in some directions and it's flat in others," Malin said. "Much of the topography is probably related to the large number of craters on the surface. We're seeing not only overlapping ejecta blankets, but probably the effects of non-symmetric ejection of materials. They're not rays in the classic lunar sense, mounds of material that were thrown out in different directions.

"Add it together and you get a relatively humpy, or rough topography. The relief on these things is very small, much less than a couple of meters, from a few centimeters up to probably two meters on the largest relief. Stereo pictures we get very much exaggerate that. What that tells you is we're not looking at the pristine original surface out there. You can see that from the fact that there are big hills to the south and east of us that are a hundred meters high. They had to have been built and the material around them has had to have been removed, so we're not looking at a pristine surface."

Scientists are hopeful Spirit will be able to resolve the mystery once it begins its surface exploration.

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