While the media’s attention has been focused on the new Mars rover Curiosity, the older Opportunity has been quietly plugging away since January 2004 - that is, until now.

Mission controllers learned on April 27 the robot had switched into a type of standby mode on its own after a period of minimized communication during the latest solar conjunction, during which the red planet passed nearly behind the sun.

Initial indications suggest the rover sensed something wrong while performing a routine camera check of the clarity of the atmosphere on April 22, according to a statement released by NASA’s Jet Propulsion Laboratory.

“Our suspicion is that Opportunity rebooted its flight software, possibly while the cameras on the mast were imaging the sun,” said Mars Exploration Rover Project Manager John Callas. “We found the rover in a standby state called automode, in which it maintains power balance and communication schedules, but waits for instructions from the ground. We crafted our solar conjunction plan to be resilient to this kind of rover reset, if it were to occur.”

Curiosity, on the other hand, reported coming through the conjunction in full health; controllers plan on issuing the first set of post-conjunction commands to the rover on May 1.

As of January of this year, Opportunity had driven a total of 22.03 miles since it first landed.

The rover’s original assignment consisted of working for three months, driving about 2,000 feet and providing the tools for researchers to investigate whether the area’s environment had ever been wet. However, during those first three months the rover transmitted evidence back to Earth that water long ago soaked the ground and flowed across the planet’s surface.

In all, Opportunity has operated on Mars 36 times longer than the three months planned as its prime mission, during which time it has driven across the plains of Meridiani to successively larger craters for access to material naturally exposed from deeper, older layers of Martian history.