June 25, 2004
Mars Rover Surprises Continue; Spirit, Too, Finds Hematite
On challenging slopes that NASA's Mars rovers began exploring this month, both Spirit and Opportunity have found new surprises for the folks back home.
Spirit rolled up to a knobby rock just past where the "Columbia Hills" start to rise from the surrounding plain. It touched the rock with a mineral-identifying instrument at the tip of its robotic arm and detected hematite. Hematite identified from orbit was NASA's key reason for choosing Opportunity's landing site halfway around Mars from these hills within Gusev Crater.
Opportunity, continuing its descent into "Endurance Crater," has found unexpected similarities between lower layers of rock it is examining for the first time and an overlying layer at "Eagle Crater" where, months ago, the rover discovered evidence that water once soaked the area.
"It's gratifying how well these machines keep performing, considering they've now nearly doubled their original three-month missions on Mars," said Chris Voorhees, rover mechanical systems engineer at NASA's Jet Propulsion Laboratory, Pasadena, Calif. By the end of next week, Spirit will have worked on Mars for half a year. It has driven more than three times the design requirement of one kilometer (0.6 mile). The only symptom of wear or aging on either rover so far is increased friction in one wheel on Spirit. The rover team at JPL is beginning to consider good sites for the solar-powered robots to spend the period of martian winter when reduced daily sunshine cuts power supply to a minimum. In the nearer term, though, team members are eager to follow through on the new scientific findings.
Spirit's hematite finding is in a rock dubbed "Pot of Gold," about the size of a softball. "This rock has a shape as if somebody took a potato and stuck toothpicks in it, then put jelly beans on the ends of the toothpicks," said Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the rovers' science instruments. "How it got this crazy shape is anyone's guess. I haven't even heard a good theory yet."
Dr. Doug Ming, a rover science-team member from NASA's Johnson Space Center, Houston, said, "There's apparently some type of weathering, a removal of material, but we're still trying to determine whether it's by chemical or mechanical processes."
Further study of Pot of Gold could also help scientists assess what the hematite in it tells about past environmental conditions. "Hematite can form in a few different ways. Most of them require water, but it can also result from a dry, thermal oxidation process," Ming said. "It was hematite identified from orbit that made Meridiani Planum a compelling place to send Opportunity. There, we've learned that the hematite is indeed part of a water story. At Gusev we're just at the starting stage.
After examining Pot of Gold with the microscopic imager and two spectrometers on Spirit's arm, the rover backed away from the rock to re-approach at a better angle for using its rock abrasion tool to expose the rock's interior. In the rough and slippery terrain, that maneuver took several days. The Other nearby rocks may also be inspected before Spirit resumes longer drives exploring the Columbia Hills area. Also, engineers are planning an attempt to redistribute lubricant in Spirit's balky right front wheel before the rover leaves its current vicinity.
Team members presented both rovers' status at a press conference at JPL today. Opportunity has driven far enough into the stadium-sized Endurance Crater to put it within arm's reach of three layers of rock beneath a sulfate-rich layer. That area is similar to what Opportunity first examined in the shallower "Eagle Crater," where it landed in January. "We're trying to systematically characterize the stratigraphy of the crater as we drive down, analyzing each unit chemically and mineralogically with all the instruments available," said Nicholas Tosca, a science-team affiliate from the State University of New York, Stony Brook. The first two newly accessed layers resemble the upper layer in having sulfate salts and spherical concretions; both are signs of formation of the rocks under wet conditions.
Squyres said, "I had thought we might see just basalt below the top salty layer, but instead it's salty as far as we've been able to see so far. Every time we see more sulfates as we work down this stack, it adds to the amount of water that was necessary to make this happen."
May 26, 2004
Mars Exploration Rover Mission Status
NASA's solar-powered Mars Exploration Rover Opportunity is beginning on Thursday what controllers expect to be frequent use of an overnight "deep sleep" mode to stretch the robot's power supply.
Opportunity has managed only one to two hours of activity on many recent days while it has been examining a stadium-sized impact crater from vantage points around the rim. Shutting down more completely overnight will conserve enough battery charge to add several hours of science operations during the day, according to Jim Erickson, Mars Exploration Rover deputy project manager at NASA's Jet Propulsion Laboratory, Pasadena, Calif.
There is a calculated tradeoff - an increased risk that, without an overnight heater running, one of the six scientific instruments might be disabled by the cold. The susceptible instrument is Opportunity's miniature thermal emission spectrometer, called the Mini-TES. It makes infrared observations used for identifying minerals from afar to help the science team decide where to send the rover. Its observations also provide close-up evaluation of rock and soil targets, and thermal information about surface materials and the atmosphere. "The Mini-TES gives us vital insight into the minerals in rocks and the role of liquid water in their formation, so this choice is a carefully considered decision to weigh the risk of losing this capability against the benefit of continuing and increasing Opportunity's ability to do all the other exploration-oriented things this rover can do," said Dr. Jim Garvin, lead scientist for Mars and lunar exploration at NASA Headquarters, Washington, D.C.
Both Opportunity and its twin rover, Spirit, have already provided several weeks of bonus operations after successfully completing their primary missions: three months of examining geological evidence about past environments at their landing sites.
As the Mars' southern-hemisphere winter advances and dust accumulates on the solar panels, the amount of electricity the rovers can generate is decreasing. The decline is more serious for Opportunity because the robotic arm of that rover has a heater with a malfunctioning switch. The switch cannot be turned off. A properly functioning thermostat turns the heater off during the day, but the heater stays on overnight even when it's not needed. The amount of energy wasted was not enough to hinder Opportunity from succeeding in its primary mission, but is now sapping about one-third of the rover's diminished amount of solar-generated electricity.
"Deep sleep gives us a way to turn that heater off overnight," said Opportunity Mission Manager Matt Wallace of JPL. The capability to do so results from a software upgrade transmitted to both rovers in April. The first use of deep sleep, on Opportunity on May 6, verified its benefit to the useful power supply.
Dr. Steve Squyres of Cornell University, Ithaca, N.Y., principal investigator for the rovers' science instruments, said, "Deep sleep is going to buy us back a huge amount of capability to drive farther, take more pictures, use the arm more." The deep sleep mode turns off a heater for the miniature thermal emission spectrometer as well as the troublesome heater in the arm. The spectrometer's heater uses less power but provides important protection. Scientists and engineers decided not to use deep sleep again after May 6 until the spectrometer had completed high-priority observations from two different overlook points of the crater informally named "Endurance." Those observations were completed Tuesday.
Tests on Earth indicate the spectrometer's beam splitter, a disc of potassium bromide salt about the size of a four-coin stack of quarters, would become ruined somewhere in the temperature range of minus 50 to minus 60 degrees Celsius (minus 58 to minus 76 degrees Fahrenheit).
Dr. Phil Christensen of Arizona State University, Tempe, lead scientist for the instrument, said, "The thermal models predict that with deep sleep, we'll go to about minus 48 Celsius. That has me concerned because it's getting close." The May 6 deep sleep did no damage, but next time the temperature could go lower, and it probably will drop lower during deep sleep later in the martian winter. Christensen concurs with the decision to take that risk in order for the rover to have adequate power for its other activities. "We always knew that as dust built up and we ran low on power, eventually there would come a time when we couldn't use the Mini-TES heater," he said. "We're getting to that point sooner because of the stuck heater on the arm."
Meanwhile, engineers and scientists are assessing how well Opportunity would be able to climb out of Endurance Crater. The assessment will aid in deciding whether to send the rover into the crater for up-close examination of rock layers there. Opportunity may complete a circuit around the crater's rim by mid-June and be ready for a decision about entering the crater.
Spirit, halfway around Mars, resumed normal operations May 23 after engineers diagnosed a software glitch that halted the rover's activities on May 21. The symptoms resembled a problem seen about a week earlier, where again the computer encountered a conflict between two onboard tasks. However the errors are understood and the two incidents are unrelated.
If they recur, neither pose a threat to the rovers' health. Spirit is now less than 700 meters (0.4 miles) from the base of the "Columbia Hills," having traveled more than 2.5 kilometers (1.5 miles) since landing. Controllers are optimistic that Spirit will reach the base of the hills by mid-June.
May 6, 2004
Mars Rover Arrival at Deeper Crater Provides a Tempting Eyeful
Scientists and engineers celebrated when they saw the first pictures NASA's Opportunity sent from the rim of a stadium-sized crater that the rover reached after a six-week trek across martian flatlands.
Multiple layers of exposed bedrock line much of the inner slope of the impact crater informally called "Endurance." Such layers and their thicknesses may reveal what the environment on Mars was like before the salty standing body of water evaporated to produce the telltale rocks that were explored in the tiny "Eagle" Crater. That's where Opportunity spent its first eight weeks on Mars.
"It's the most spectacular view we've seen of the martian surface, for the scientific value of it but also for the sheer beauty of it," Dr. Steve Squyres of Cornell University, Ithaca, N.Y., said about a color panorama of Endurance Crater released at a news conference today at NASA's Jet Propulsion Laboratory, Pasadena, Calif. He is the principal investigator for the science instruments on both Opportunity and its twin Mars Exploration Rover, Spirit.
In coming days, Opportunity will circle the rim of Endurance, observing the crater's interior from various angles. Scientists and engineers have begun to identify interesting science targets and assess how difficult it would be for the rover to descend partway into the crater and climb back out. "We will need to decide whether the science is compelling enough to send the rover into a crater it might never leave, or whether to explore other sites first before entering Endurance," said Orlando Figueroa, director of the Mars Exploration Program, NASA Headquarters, Washington.
At Eagle Crater, an outcrop of bedrock only about the height of a street curb yielded evidence that the site was once covered by a body of salty water deep enough to splash in. "That was the last dying gasp of a body of water," Squyres said. "The question that has intrigued us since we left Eagle Crater is what preceded that. Was there a deep body of water for a long time? Was there a shallow, short-lived playa? We don't know."
The strategy for seeking answers is to examine older rocks from deeper layers, so Opportunity was sent on drives totaling about 800 meters (half a mile) to reach the deepest crater nearby, Endurance. This crater excavated by the impact of a tiny asteroid or a piece of a comet is about 130 meters (430 feet) wide and, from the highest point on the rim, more than 20 meters (66 feet) deep, 10 times as deep as Eagle. An exposure of outcrop in a cliff high on the inner wall across from the rover's current position reveals a stack of layers 5 to 10 meters (16 to 33 feet) tall. Other exposures around the inner slope of the crater may be more accessible than the cliff, and chunks from the same layers may have been thrown out onto surrounding ground by the crater-forming impact.
"There is a rock unit below what we saw at Eagle Crater," Squyres said. "It looks fundamentally different from anything we've seen before. It's big. It's massive. It has a story to tell us."
Brian Cooper, leader of JPL's squad of rover drivers for Spirit and Opportunity, said the initial view of the crater doesn't settle accessibility questions yet. "The slope right in front of us averages 18 to 20 degrees. Getting into the crater is no problem, but we have a lot more work to do to assess whether we could get back out. That depends on soil properties and slippage, as well as slope." The planned circuit around the rim will also require careful navigation. "If you don't go close enough to the lip, you can't look in, but if you go too far, you could fall in," he said. "We're going to have a very interesting few weeks."
When NASA sent astronauts to the lunar surface more than 30 years ago, it was decided not to allow them to enter craters as fresh and steep as Endurance, but Opportunity may be able to do what no human has done before on another planet.
Scientists and engineers working with the other rover, Spirit, are also examining images of a destination area to identify possible targets of study and to assess how well the rover can get to them. However, that destination area, informally named "Columbia Hills," still lies several weeks of travel ahead of Spirit. Images and surface-temperature information from the NASA orbiters Mars Global Surveyor and Mars Odyssey are supplementing Spirit's own increasingly detailed pictures of the hills. Nighttime surface temperatures indicate that some areas within the hills are rockier than others, said Amy Knudson, a rover science team collaborator from Arizona State University, Tempe.
"The hills represent a different rock unit, likely older than the plains we're on," Knudson said. "There are intriguing features in the hills and we want to investigate the processes that formed them. We're especially interested to see if water played any role."