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Parting shots from a Mars rover

NASA / JPL / Univ. of Ariz.

An image captured by NASA's Mars Reconnaissance Orbiter on March 31 shows the glint of the Spirit rover's solar panels as a bright spot toward the left side of this image, alongside the rock formation known as Home Plate.

NASA is no longer sending commands to the Spirit rover on Mars, but the long-silent robot still has a few more chances to phone home. Not that anyone is expecting Spirit to call, more than a year after the six-wheeled robot went into a coma. But if Spirit does decide to make a resurrection, it better do it before June 8.

That's when NASA's Mars Odyssey orbiter is due to take a last listen for UHF signals from the rover, which is mired in sandy soil on an incline inside Gusev Crater, alongside a rock formation known as Home Plate. The final relay pass is due at 12:30 p.m. PT (3:30 p.m. ET) on June 8, said John Callas, project manager for the Mars rover missions at NASA's Jet Propulsion Laboratory in Pasadena, Calif.

"After that point, there is no attempt at communicating with Spirit going forward," Callas told me today.

So when do you mark the time of death? Would it be June 8? Or May 25, when NASA sent its last command seeking contact? Or March 22, 2010, the last time that NASA heard from the ailing, energy-starved rover?

Callas and his colleagues have had a long time to prepare for Spirit's end and turn their full focus to the twin rover Opportunity, which is still very much alive and rolling.

"The transition to single-rover operations has already been done," Callas said. "That was done many months ago. The project is already where it should be."

He said mission operations at JPL now occupy the time of a little more than 40 full-time-equivalent employees, compared with several hundred back in the heyday of the rover missions, seven years ago. The cost for the Opportunity-only operation is about $12 million annually, compared with $800 million for the rovers' construction, launch and primary mission.

Mission team members reflect on the Spirit rover's journey.

At the risk of anthropomorphizing the machine yet again, I'll just mention that Spirit was generally considered the hard-working, nothing-comes-easy rover, while Opportunity was the "little princess" of the two. Spirit was the first to land on Mars, in early January of 2004, and it suffered glitches that the team could use to smooth the way for Opportunity later.

Many of Spirit's most memorable discoveries, having to do with geological evidence of ancient water on Mars, came after its scheduled 90-day primary mission was finished.

"It's all been said, and everyone knows this, that this is a remarkable mission that exceeded expectations, a three-month mission that lasted for six years," Callas said. "We have to remember how blessed we are to have had that. Our glass isn't half-empty, it's really nine-tenths full."

As the mission wore on, Spirit had to contend with a bum wheel and bouts of computer-memory amnesia, but its final round of troubles got started a little more than two years ago when it became stuck in loose dirt while driving around the Martian plateau known as Home Plate. For months, engineers at JPL worked on detailed plans to free up the rover, but they just couldn't move Spirit far enough to put its power-generating solar arrays into a good position to soak up sunlight during the Martian winter.

For a while, NASA used Spirit as a stationary observation post, but the rover's power eventually dwindled to the point that it shut down transmissions to Earth and went into hibernation.

It never woke up.

Ironically, it was Spirit's solar panels that most recently signaled the rover's location. This March, sunlight glinted off the panels at just the right angle to shine into the high-resolution camera on NASA's Mars Reconnaissance Orbiter. The flash told the mission team that Spirit's panels were not yet completely covered with the red dust of Mars.

I asked Callas whether it was worth monitoring the reflections of Spirit's solar panels to track the deposition of dust over the months and years to come, but he said that would be a "very difficult analysis to do." The reflectance of the panels could be anywhere between 30 and 80 percent.

"It's unclear how you can use that information," Callas said.

Kenneth Kremer / Marco DiLorenzo / NASA / JPL / Cornell

The Spirit rover's last panorama, sent back in February 2010, shows its surroundings in Mars' Columbia Hills. The hill with the light-colored top, visible near the top center image, was dubbed Von Braun and would have been Spirit's next destination.

So Spirit's days as a scientific instrument of any kind appear to be over. But scientists will continue to pore over the data that Spirit delivered for more than six years. "That will happen for decades," Callas said. And as an inspiration for future planetary science, Spirit has entered immortality, alongside the Mars Viking landers as well as the Mars Pathfinder lander and Sojourner rover.

It's fitting, then, that the rover will get the scientific community's equivalent of an Irish wake in July, when the rover science team gathers at JPL for a previously scheduled meeting. "We intend to use that opportunity as an avenue for Spirit's send-off," Callas said.

Godspeed, Spirit! And may you be in heaven half an hour before the Great Galactic Ghoul knows you're dead.

More about Mars:

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