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Has Spirit Found Bedrock in Columbia Hills?
Since arriving at the Columbia Hills, Spirit, one of the Mars Exploration Rovers, has encountered some mysterious phenomena. The rover’s right front "arthritic" wheel that plagued Spirit’s 2-mile trek across the plains is now suddenly working perfectly and the once dust-covered solar panels whose power output was cut in half have now been miraculously wiped clean. But the biggest mystery of the Columbia Hills may lie in the angled rock outcrops that Spirit has found in the vicinity of "Larry’s Lookout" on Husband Hill.
In December of 2004, the mission scientists for the Mars Exploration Rover Spirit spied a ridge near the top of Husband Hill, one of the seven Columbia Hills located near the middle of Mars’ Gusev Crater. Steve Squyres, Principal Scientific Investigator for the MER Mission, started calling the ridge "Larry’s Lookout" and the mission team decided to send Spirit to that ridge to determine what it was and use it as a "perch" to take a panorama of the valley that it overlooked. They knew it would be a challenge given the sand, steep slope, and rocks in the area, but the scientists are now discovering that the arduous climb was well worth it. According to one geologist, what Spirit is finding at Larry’s Lookout could turn out to be one of the highlights of the MER mission.
The "Larry" of Larry’s Lookout is Dr. Larry Crumpler; field geologist, volcanologist, and Research Curator at the New Mexico Museum of Natural History and Science in Albuquerque, New Mexico. He is also a mission scientist for MER.
Spirit had originally approached and climbed Larry’s Lookout from the rear, and from that perspective the Lookout appeared to be just a knob on the hill.
But then the rover moved around to the side of Larry’s Lookout, and took a picture that caught the immediate attention of Squyres and other mission scientists. The image looks north along the ridge of the Columbia Hills with Spirit sitting on Husband Hill, and the camera pointed at Clark Hill. The hills are strewn with rocks, and in the foreground are two tilting rocks. The big outcrop just behind the rocks is Larry’s Lookout.
Dr. Crumpler explained the image and the questions it provoked: "From this perspective, we can see that the outcrop has a tilted look. The two boulders in front of the outcrop appear to be orientated in the same direction. And in the hill in the distance to the right you can see layers that appear to be oriented at the same angles. And to the left, there are outcrops that are oriented at exactly the same angle. The overall impression is that there is some sort of organized layering or structure to the hills. Our big question is, is it just something draped over top of the hills, like ash fall draped over it like snow, or is it an indication of the internal arrangement of the bedding planes in the hills? Did the hills originally form by bulging up, and were the beds originally horizontal? Or did some sort of weathering occur? Any of those interpretations are interesting because it says something has happened subsequent to the original formation of the rocks and hills themselves."
Crumpler said that this is one of the most interesting areas that Spirit has yet encountered, and the first indication of extensive bedrock. "For the first time we have started to feel hopeful that we can make sense of the Columbia Hills," he said. "I think it is going to be a highlight of the mission."
Crumpler says they are seeing evidence of finely bedded materials in the rocks, with very fine laminations that signify bedded, sediment-like materials. "This all indicates that we’re not just looking at volcanic rocks or old broken up rocks, but there is some sort of organized layering," he said. "We’re going to do a full scale campaign to try to understand all of these things." Although the MER science team still has a plethora of unanswered questions about this area of the Columbia Hills, from the evidence so far, water is likely to be at least part of the final equation.
Spirit is just about to begin studying the rock outcrop informally dubbed "Methuselah," just to the left of the rover tracks in the image. "Spirit is looking at this outcrop that is dipping to the northwest and looks like it is laminated with bedding planes," said Crumpler. "It is a foot-high outcrop with an odd angle that indicates structure or a deposition that took place on a slope."
Over the weekend of April 23-24, Spirit was ordered to take a panoramic image of the outcrop in order to give the scientists an overview of the overall pattern and layout of the area.
Crumpler noted that there is a considerable age difference between the Columbia Hills and the lava plain that Spirit crossed to reach the Hills. He likened the Hills to a sandstone butte surrounded by fresh, young lava flows, similar to the landscape that is found in the United States’ Southwest. "The Hills are much, much older," Crumpler said. "You can actually see the contact between the two where the lava flows sort of lapped up on the edges of the Hills. When you cross that boundary you go from the basalts which show only small amounts of weathering and alteration to the rocks on the Columbia Hills that are totally 'grunged-up’ and altered, and basically water-soaked at some time in their history."
"We’re still trying to figure out what’s going on here," Crumpler added, "but the outcrop we are looking at is giving us some good clues."
Crumpler has had extensive experience in field geology, and said he has spent a lot of his time walking across New Mexico’s lava flows, just as Spirit trekked across the lava flow in Gusev Crater. He’s always had an intense interest in the geologic exploration of other planets and has been involved in some of the mapping programs of Mars, Venus and Io. But he says the MER program is the most exciting mission of which he’s been a part.
"Everyday there has been something different that we hadn’t seen the day before, or some new perspective of the terrain, so I always say that 'today’ is the most exciting part of the mission."
"When you’re in the field," he continued, "you keep moving because you’re always curious about what you’re going to find at the next outcrop that will tell you more about what you are trying to figure out. But we are very likely to be here (at Larry’s Lookout) for a long time giving this outcrop our full attention."
So, it appears Larry’s Lookout will be keeping Spirit and the MER scientists busy for awhile, as they try to unravel the mysteries of the Columbia Hills.
Written by Nancy Atkinson
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