We knew this time would eventually come: NASA's Jet Propulsion Lab, which runs the two Mars rovers, acknowledged today that Spirit, which has been exploring the Martian surface since January 2004, may have been heard from for the last time.
You may recall that the Spirit rover got stuck last year on the edge of a small crater, and when controllers on earth couldn't free it after months of trying, they knew the clock was ticking.
Among other things, they couldn't move the rover to a sun-facing slope for the six-month-long Martian winter, so that its solar panels could gather at least enough energy to run heaters and the rover's radio system. The solar panels, as chief scientist Steve Squyres told us a few years ago, are essentially useless unless the sun shines almost directly down on them.
Without heaters, the temperature of the rover's electronics, NASA says, probably dropped to something like 65 degrees below zero Fahrenheit.
The winter is over now at Gusev Crater, and engineers thought this might be the first week Spirit would have enough power to send at least a beep in response to signals from earth They called it. No joy.
"It will be the miracle from Mars if our beloved rover phones home," said Doug McCuistion, director of NASA's Mars Exploration Program, in a statement today for reporters. "It's never faced this type of severe condition before -- this is unknown territory."
Spirit's twin, Opportunity, is still working on the opposite side of the planet, making a forced march toward a large crater called Endeavour. And Spirit may be heard from yet, though the chances are dwindling.
A reminder: NASA's gotten its money's worth out of the rover. When it landed, mission managers (perhaps playing down expectations), plotted out a mission that would last 90 "sols," or Martian days. Today was sol number 2,337.
There will be no truly final moment for Spirit, no confirmation that it has actually stopped operating. But at some point, NASA managers will have to decide that the mission is over, pay one last tribute, and move on.