Good moves on Mars

If you're a fan of NASA's Mars missions, a few things have started heading in the right direction - including a renewed flow of eye-pleasing pictures from the Mars Reconnaissance Orbiter, a new program that gives you a say in picking the orbiter's future targets, and new signs of progress in the months-long effort to free the Spirit rover from a sand trap.

Spirit: Free at last? There's new hope

For the past nine months, Spirit's wheels have been stuck in a patch of soft soil nicknamed Troy. Mission managers at NASA's Jet Propulsion Laboratory tried for weeks to free the rover by having it retrace its tracks - but instead, the wheels just dug themselves in deeper. And as if that wasn't bad enough, the rover team discovered that the rover's right front and right rear wheels weren't working. That left the six-wheeled Spirit with just four good wheels.

Last week, managers tried a different tack: Instead of trying to get out the way it got in, Spirit was commanded to continue on the southward path it was taking when it got stuck. (Describing the direction is a little tricky. Because of its long-running wheel problems, Spirit was rolling in reverse gear when it got into trouble. So it has to "drive forward" to retrace its steps, and "drive backward" to break new ground. Spirit is now trying to drive backward, rear wheels first.)

The rover drivers also added a new maneuver that involves turning the wheels from side to side before a drive is attempted. The maneuver, called a "frog kick" or "breaststroke," is aimed at shaking dust out of the wheels and clearing the path ahead, said John Callas, project manager for the twin rover missions. Each wide turn of the wheel pushes against the soil piled up behind it, giving the rover an extra push forward.

"Think of it like trying to do a breaststroke while you're lying in snow," he told me.

However you visualize it, the frog kick seems to be working. Callas said Spirit has moved about 3 centimeters (1.2 inches) after each kick-and-drive maneuver. He estimated that the rover has plowed about 7 centimeters (3 inches) southward through the sandy soil so far.

That may not sound like much, and Callas cautioned that the maneuvers might get the rover only so far before it becomes fully stuck again. But in this case, every inch helps.

"The rear wheels are climbing up. ... It's jacking up the rear of the rover," Callas said. That's a good thing, because that has the effect of tilting Spirit's solar arrays more directly toward the sun in the north. That should let Spirit soak up more sunshine during the depths of the southern Martian winter, which lasts from about mid-February to mid-August, Callas said.

"We're trying to increase the rover's tilt to enhance its winter survivability," he explained.

All this is good news for the rover team, but Callas peppered his remarks with caution. Spirit still isn't tilted toward the north as much as it should be. If the rover gets stuck again, there's a chance its solar arrays won't generate enough power to keep it alive through the winter.

During the most recent drive, Spirit's left middle wheel stalled - which is an ominous sign. "We may be observing a rapid deterioration in the mobility system," Callas said.

At one point there had been talk about using Spirit's robotic arm as a pusher or a plow, but engineers figured out that the arm would be of little or no help in such maneuvers. Even if Spirit loses its mobility, NASA is still hoping the rover can serve as a stationary science outpost. The robotic arm can serve as a valuable tool for doing science in place, but using it to move rocks or soil would put that part of the mission at risk, Callas said.

"That's not going to happen," he said.

For more about Spirit's situation, check out this status update from the Jet Propulsion Laboratory, complete with a larger animated image of the wheels' movement. You can also get the latest on Spirit's twin, Opportunity, which is in the middle of a months-long trek toward Endeavour Crater.

Mars Reconnaissance Orbiter: Pick your picture

While the rover team focuses on Spirit's predicament, the scientists and engineers in charge of NASA's Mars Reconnaissance Orbiter's high-resolution camera are reveling in the fresh flow of imagery after the probe's revival last month. They're also enlisting the public to help select future targets for picture-taking.

The team behind the High Resolution Imaging Science Experiment, or HiRISE, has established a Web-based suggestion box called HiWish. Once you register on the Web site, you can use a map-style interface to point to areas you'd like to have HiRISE photograph. You'll be asked to explain the rationale for your choice and show how it fits in with the mission's science themes.

The HiRISE science team will evaluate the suggestions and go after the high-priority targets first. You'll be notified if and when the orbiter sends back a picture of your suggested site. "This opportunity opens up a new path to students and others to participate in ongoing exploration of Mars," Rich Zurek, the Mars Reconnaissance Orbiter's project scientist, said in a news release.

McEwen had a few tips for folks who want to maximize the chances that their suggestion will be chosen:

• Don't spam the system: This is not a lottery, and it's not a contest to see which locations get the most votes. People who send in multiple entries for the same target will not increase their chances of winning. "If they annoy us, they're less likely to get their picture taken," McEwen said.
• Don't choose the popular places: HiRISE has taken thousands of pictures so far, and yet less than 1 percent of the Martian surface has been imaged. Places like the Face on Mars and the roverlandingsites have already had their day in the spotlight, but there are plenty of other worthy areas that haven't gotten as much attention. Try to put your cursor "on a place on Mars that isn't really popular," McEwen said.
• Go north ... or south: Because the probe traces a pole-to-pole orbit, there are more opportunities to take pictures of high-latitude targets than equatorial targets.
• Think small: HiRISE is capable of seeing objects just a few meters wide, but it's not good at seeing the big picture. "The most common mistake that people are likely to make is thinking at the wrong imaging scale," McEwen said. Don't bother to suggest taking a wide-angle shot of Olympus Mons or Valles Marineris.
• Do your homework: Checking out the pictures already taken is the best way to get a sense of what the HiRISE team is looking for. Even if you never make a suggestion, you're sure to come across images that will make your head spin. Our selection of "High-Resolution Hits" merely provides a Top 10 taste. Fresh images are added to HiRISE's database every week.

The latest crop includes a colorful view of streaked bedrock in the central pit of an impact crater - the image at the top of this posting. The colors have been "stretched," or enhanced, to reflect shades of blue, rose and purple that you'd never actually see on the Red Planet. In this case, the different shades reflect subtle variations in surface composition.

The swirls of color show where Martian bedrock "is eroding, moving downhill a bit, then getting swept by the wind," said Alfred McEwen, principal investigator for the High Resolution Imaging Science Experiment, or HiRISE.

Another HiRISE image shows a layered mesa that looks like a blue-and-tan racetrack. This feature is part of a Martian shield volcano known as Syrtis Major, near the northwest rim of a giant impact basin called Isidis Planitia. The area is considered a potential landing site for the Curiosity rover (a.k.a. Mars Science Laboratory). McEwen told me the site is of interest because it has a "great diversity of minerals," including hydrated minerals that may signal the area was hospitable to life billions of years ago.

If HiRISE images indicate that the spot is sufficiently safe for landing, it could be visited by Curiosity in 2012 or by a U.S. or European rover in 2018-2019.

Phoenix Mars Lander: No resurrection yet

Mars' northern hemisphere is just now coming out of the winter season, and scientists are trying to find out whether NASA's Phoenix Mars Lander has resurrected itself. They're not holding their breath.

Phoenix stopped communicating with Earth back in November 2008, at the end of a mission in Mars' north polar region that lasted more than two months longer than its expected three-month duration. The probe's most celebrated finding was the discovery and analysis of water ice beneath the Martian surface.

The Phoenix team knew that the probe would freeze to death during the winter, but they built a "Lazarus mode" into its software, just in case the electronics returned to working order after thawing out. This week, NASA's Mars Odyssey orbiter started listening for signals from Phoenix, but as of today, nothing has been heard. Off-and-on listening sessions will continue for the next couple of months - just in case Phoenix rises from the grave after all.

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