NASA said on Tuesday that it was abandoning efforts to get back in touch with Spirit, one of the two rovers on Mars. Spirit, which has been stuck in a sand trap for two years, fell silent last year as winter arrived and its solar panels could no longer generate enough electricity. Engineers had hoped that the rover would revive when spring returned, but they never heard from it again.
Now, as the Martian days grow shorter, Spirit’s managers decided that it was not worth the time and money to continue.
“We couldn’t recover any of the approved science objectives that we had for Spirit even if we heard from the rover, which is very unlikely,” said John Callas, the project manager for Spirit and its twin, Opportunity, which continues to operate on the other side of the planet.
The last set of commands to Spirit will be sent early Wednesday morning.
The Spirit and Opportunity rovers landed on Mars in January 2004, their original mission scheduled to last just three months. At first, it did not seem that Spirit would last even that long. A computer memory glitch disabled it three weeks after landing.
After engineers diagnosed and fixed the problem, the two rovers defied expectations with each passing anniversary. Both discovered evidence that Mars, which is cold and dry today, once had plentiful water at its surface.
Spirit did age over time. In 2006, its right front wheel failed. From then, it mostly drove backward, dragging the lame wheel through the soil. “It reveals stuff below the surface, and it reveals stuff that we would have just driven by because it’s camouflaged under the ground,” Dr. Callas said.
One of those discoveries was a material called amorphous silica, which scientists believe formed in an ancient hydrothermal system.
In May 2009, Spirit’s wheels broke through a thin crust into a hidden sand trap. Attempts to get it out only drove it deeper. Then a second wheel failed.
Last year, NASA announced that Spirit would continue operations as a stationary science station, observing the atmosphere and measuring the wobble in Mars’ axis of rotation. 
But winter was approaching, which proved to be Spirit’s demise.
Opportunity is continuing its drive to a large crater named Endeavour, where scientists hope it will offer a close-up view of clay deposits that have been observed from orbit.
Clay forms in water, and the minerals left behind could provide important new clues about the history of Mars.
At its current pace, and if all goes well, Opportunity could arrive at Endeavour by the fall.