The Opportunity rover broke a 28-year-old Mars duration record Thursday, surpassing the Viking 1 lander to become the longest-lived spacecraft to ever operate on the Red Planet, at least until the identical Spirit rover awakes from a winter snooze.

Opportunity's navigation camera captured this recent image of its tracks at Meridiani Planum. Credit: NASA/JPL-Caltech

Opportunity is now driving across a flat equatorial plain toward Endeavour crater, a 14-mile-wide, 1,000-foot-deep impact site still months away from the golf cart-sized rover.

Spirit likely already holds the endurance record, but officials at the Jet Propulsion Laboratory in Pasadena, Calif., won't know for sure until the crippled rover wakes up from a winter hibernation later this year.

"Opportunity, and likely Spirit, surpassing the Viking Lander 1 longevity record is truly remarkable, considering these rovers were designed for only a 90-day mission on the surface of Mars," said John Callas, the rovers' project manager at JPL.

Controllers haven't heard from Spirit since March 22, when engineers believe the rover's solar panels stopped producing enough electricity to operate the craft's communications system. In such an event, Spirit was programmed to go into hibernation with keep-alive heaters turned on to wait out the cold and dark winter.

The rovers reached the Martian winter solstice May 12, the point where the least sunlight reaches their solar panels. Managers expect Spirit's power situation will improve in the coming months.

Spirit has been stuck in a sand pit for more than a year, and its solar panels were left pointed away from the sun, which is low in the sky in the Martian winter. The attitude left Spirit without enough power to stay operational through the winter, forcing the rover into a winter snooze for the first time since it landed.

"Spirit has likely passed that record, but right now, Spirit is deeply asleep," Callas said. "We haven't heard from the rover in about two months, but once she wakes up, she'll reclaim the title of longest-lived asset on the surface of Mars."

Replica of a Viking lander. Credit: NASA

Opportunity surpassed the previous record of six years and 116 days, which was set by the Viking 1 stationary lander after it touched down on the western slope of Chryse Planitia in the Martian northern hemisphere on July 20, 1976.

One of two identical landers dispatched to Mars in 1975, Viking 1 was the first U.S. spacecraft to land on Mars and return pictures. It continued returning data until NASA last heard from the lander on Nov. 11, 1982.

Viking 2 successfully landed in September 1976 and stopped functioning in April 1980.

Like the famous Spirit and Opportunity rovers, the Viking landers were originally designed to operate for just 90 days.

Spirit and Opportunity touched down on Mars three weeks apart in January 2004.