After months of tests and analysis, engineers plan to beam commands to NASA's Spirit Mars rover Monday, kicking off a long-awaited attempt to free the hardy craft from the talcum powder-like soil of a hidden crater that trapped it last April.
"Spirit's facing the most challenging situation it's seen yet on the surface of Mars," Doug McCuistion, director of NASA's Mars exploration program, said Thursday. "We know a lot of people around the world...view Spirit with great affection, exploring the Red Planet along with it, experiencing the excitement, seeing new and exciting vistas, seeing new landscapes, uncovering some incredible new knowledge about our sister planet.
The view from the Spirit rover looking north, back along its path, from the point where it got trapped last April. The rover is believed to be straddling the rim of a hidden crater. Note the front-left wheel, nearly buried in powdery soil.
(Credit: NASA)"I'd like everybody to be hopeful, but I'd also like them to be realistic," he said. "If Spirit cannot make the great escape from this sand trap, it's likely that this lonely spot, straddling the edge of this crater, might be where Spirit ends its adventures on Mars."
Designed to operate for just three months on the frigid surface of Mars, Spirit and its twin rover, Opportunity, have been exploring opposite sides of the planet since early 2004, collecting data in concert with orbiting spacecraft to help scientists understand the role of water in the Martian environment.
Chalking up a steady stream of discoveries over the past five years, the unexpectedly long-lived rovers are held in high esteem by the scientists and engineers who drive them across the surface of Mars and eagerly await the data they send back.
"In many ways, we think of these rovers kind of as our children that we've sent off into the world way too early," said Ashley Stroupe, a rover driver at the Jet Propulsion Laboratory in Pasadena, Calif. "And like most parents, when their kids go off to college, we can't reach out to help them every time they really need us. So it really is a bond, not just between us and the rover, but also the team has become a very close family as well."
Last April 23, the six-wheel Spirit was slowly rolling backward on the western side of a feature known as "Home Plate," heading toward the south and a pair of volcanic structures that scientists wanted to examine. The rover was driving backward because its right front wheel stopped working in 2006.
The ground to the south of Spirit looked normal, but as it rolled along, its wheels broke through an upper-crust-like layer of soil and into a softer, unseen material.
"Essentially, the rover was driving on what we call a dirt crust," said John Callas, the project manager of the Mars exploration rovers at JPL. "It was a hard surface that we broke through, and underneath this material, camouflaged underneath, was this loose, fine material where the rover is challenged right now."
Scientists later determined that Spirit's path was straddling the rim of an ancient, 26-foot-wide crater just beneath the surface. The crater was filled in with sulfate sands that formed layers with different compositions.
Initial attempts to drive out in a crablike fashion by turning the front and back wheels in the same direction only made matters worse.
Pictures from navigation cameras on the rover show its forward and rear wheels almost buried in the soil, their treads caked with a powdery coating that reduces traction. Even worse, photographs show a pyramid-shape rock sticking up from the soil directly below Spirit's body that threatens to rub against the belly, possibly lodging in an indentation. If the rock ends up bearing any of the weight of the rover, traction could be reduced even more.
A view under the Spirit rover showing a pyramid-shape rock close to the belly of the robot.
(Credit: NASA)NASA managers decided to halt any additional attempts to free Spirit until engineers could complete a thorough analysis using a full-scale mockup and simulated Martian soil.
"Unfortunately, Spirit may have met its match in this one," McCuistion said. "We will see if we can get it out of this talcum powder-type soil that laid beneath a seemingly innocuous surface crust that we broke through...The rover teams have been working very hard since April, they've been testing, strategizing, analyzing, and modeling to figure a way out. We even called experts in soil mechanics and mechanical systems in to try to help us understand the environment. But there's only so much you can do on Earth to simulate Mars."
Late Monday, commands will be uplinked to Spirit in an attempt to drive north, back along the furrows its wheels dug as the rover moved into the sand trap last April. Engineers will find out how the move went on Tuesday. No one expects a quick extraction, and engineers said it likely will take weeks or months to either free the rover or determine that it can't be done.
A mockup of the Spirit rover in a "sand box" at the Jet Propulsion Laboratory in Pasadena, Calif., where engineers have been testing techniques for driving the vehicle out of loose soil.
(Credit: NASA)"Our best plan at this point is to try to drive forward, retracing our steps as we drove in," Stroupe said. "And we believe this is our best plan for several reasons. One is that we believe this softer material may be easier to plow through than trying to break through the crust and cut new tracks. So if we follow our old tracks out, we may be able to make better progress.
"We have very little ground clearance under the vehicle. Wheel turns cause us to sink further into this material, and there is no guarantee that any plan we come up with will succeed in extricating the vehicle," she said. "This is going to clearly be a very long process, to either get to extrication or perhaps even to determine if extraction is going to work."
The team's progress will be assessed in February. Depending on the success or failure of the work at that point, NASA could opt to continue with additional attempts or decide to call it off. Even in that worst-case scenario, scientists could still use Spirit's instruments to study nearby rocks and soil, and to monitor the martian weather.
But Stroupe hopes it won't come to that.
"I think a lot of us, while we're waiting for that plan to execute (Monday), will not get a lot of sleep," she said. "But regardless of the outcome, none of us can have anything but primarily positive emotions about this mission. It's been such an incredible experience, we've come so far beyond what we thought we would accomplish...We're so proud of them, and we're so thrilled to have been part of this project. It will be sad to see them go. But we're not ready to let go yet, and we don't plan to let go yet. We still have a lot of work to do."
Data from a comet-bound NASA probe, a robotic mission to Saturn, and a U.S. instrument aboard an Indian spacecraft have provided clear evidence that at least trace amounts of water exist on the moon's surface, researchers said Thursday.
While scientists have long suspected that water ice from comet impacts is trapped in cold, permanently shadowed craters near the moon's poles, the new data indicates that water molecules form and dissipate across broader areas, even in lunar daylight.
Data from a NASA instrument aboard India's Chandrayaan-1 spacecraft show evidence of water molecules on the surface of the moon. Areas in blue show relatively high concentrations of water near the moon's poles.
(Credit: NASA)While the data represent a major surprise and a "really profound discovery," one scientist said, researchers cautioned that the moon remains an extremely dry place, by human standards.
"The observations presented here show a combination of hydroxyl, OH (oxygen hydrogen molecules), and H2O (water) that resides in the upper few millimeters of the lunar surface," said Jim Green, director of NASA's Planetary Science Division. "The average amount of water reported, if we were to extract it, is about a quart of water per ton (of surface soil)."
To put it another way, he said, about 16 ounces of water might be present for every 1,000 pounds of surface soil near the moon's poles. For soil near the equator, only about two tablespoons of water is believed to be present in every 1,000 pounds.
"Even the driest deserts on the Earth have more water than are at the poles and the surfaces of the moon," Green said.
But scientists agreed that the results open a new chapter in humanity's understanding of the moon and the processes at work across the entire solar system that could lead to water formation on other airless asteroids and moons.
"Having any water or hydroxyl in the sunlit areas of the moon is as surprising as it is intriguing," Bruce Betts, director of projects for the Planetary Society, said in a statement. "Will such results turn out to be the tip of the iceberg, or will the moon remain a dry desert with slightly more moisture than we thought?"
On a related front, NASA unveiled new findings from the Mars Reconnaissance Orbiter on Thursday that show clear evidence of huge subsurface ice sheets extending from the poles of the Red Planet halfway to its equator.
The buried ice was spotted in debris thrown up in five recent northern hemisphere impact craters. The ice is surprisingly pure and easy to see in high-resolution pictures from the Mars Reconnaissance Orbiter.
Scientists believe that the ice is a remnant of a more humid period in Mars' recent history, when the planet's polar ice caps extended much farther toward the equator.
A recent impact crater on Mars, showing bright ice thrown up from a subsurface layer.
(Credit: NASA)"Every indication is that this is forming a broad, continuous sheet beneath the surface," said Ken Edgett, a camera team member with Malin Space Science Systems of San Diego. "We have five separate impact sites, all showing more or less the same thing.
"I'd say the volume of water--and this is a guess--the volume of water is probably comparable to the volume we would have in, say, the Greenland ice sheet on the Earth, in the buried ice deposits (and the North Pole ice cap)."
Shane Byrne, a member of the High Resolution Imaging Science Experiment team at the University of Arizona, said the ice sheet is probably about a yard or so thick.
"These buried ice sheets that extend from the poles all the way down to 45 degrees or so (north and south latitude) don't quite cover half of the planet, but (they) come close," he said. "So we're talking about maybe a (half) million cubic kilometers of ice in total."
Water ice is a critical resource for future space travelers, as well as a requirement for the development of life as it is currently known. The presence of ice on Mars is not a surprise, although the purity and extent of the buried ice sheets is. Water on the moon, however, is another matter.
Three spacecraft--India's Chandrayaan-1 lunar orbiter, NASA's Saturn-bound Cassini probe, and the agency's Deep Impact comet mission--all detected evidence of water molecules on the moon's surface. In a surprise, it appears that water molecules are present, even in the heat of direct sunlight.
"Finding water on the moon in daylight is a huge surprise, even if it is only a small amount of water and only in the form of molecules stuck to soil," Jessica Sunshine, an astronomer at the University of Maryland who helped analyze data from NASA's Deep Impact spacecraft, said in a statement. "In the Deep Impact data, we're essentially watching water molecules form and then dissipate right in front of our eyes."
What causes the water to form is not yet clear, but Sunshine said the mechanism might involve electrically charged hydrogen ions in the solar wind interacting with oxygen-rich minerals in the lunar soil to form water and hydroxyl molecules.
"We aren't certain yet how this happens," she said, "but our findings suggest a solar-driven cycle in which layers of water only a few molecules thick form, dissipate, and reform on the surface each lunar day.
"This water is formed in the morning, substantially lost by lunar midday, and reformed as the lunar surface cools towards evening."
Finding water on the moon has long been one of the holy grails of modern lunar exploration because solar power and ice deposits, assuming they are close enough to the surface, could provide a source of water, air, and rocket fuel for future moon explorers or colonists.
The discoveries announced this week don't necessarily mean that abundant water supplies are available across the moon's surface--the solar-driven cycle implied by Deep Impact would produce only trace amounts--but they show that the moon isn't the totally dry place scientists long thought it was.
Earlier data indicated possible ice deposits in permanently shadowed craters near the moon's poles, where water from comet impacts could have been trapped over the moon's long history.
In June, NASA launched two new spacecraft to the moon, the $504 million Lunar Reconnaissance Orbiter and the $79 million Lunar Crater Observation and Sensing Satellite, or Lcross.
Orbiting the moon at an altitude of just 31 miles, the LRO spacecraft is designed to map the lunar surface in unprecedented detail to help identify possible landing sites for future manned missions. Lcross is focused specifically on water.
If all goes well, the spent second stage of the rocket that boosted LRO and Lcross to the moon will crash into a permanently shadowed crater on October 9, blasting presumably ice-bearing soil into sunlight for direct analysis by LRO, the Hubble Space Telescope and ground-based observatories. Lcross will fly through the plume, beaming back data before it, too, crashes to the surface.
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