For a rover, having a prime mission of just 90 days, NASA’s Mars rover Opportunity is definitely is going over and beyond the call of duty.

The veteran wheeled rover celebrated its 12th year on Mars on Monday. Though it’s been a tough road for the robot, it has been doing science. It’s doing science during the most aggressive about 687 Earth days long period of the Martian year.

The southern hemisphere of the Red Planet dipped into winter solstice on January 2, marking the shortest, and thus darkest, day of Opportunity’s year. This isn’t a fun time for a solar powered rover. Opportunity needs sunlight for charging its batteries, thus when daylight is limited, rover drivers have to place the rover at an optimized angle for the collection of as much of the restricted sunlight as possible.

However, there comes along some frustrating issues with its crazy-extended mission. First of all, the Red Planet dust collects on solar arrays, which further limits the amount of sunlight that can be used for charging batteries. It’s not being long, since mission engineers have started becoming more and more concerned over the viability of the rover’s solar panels; during the years if dust build up, they’d become so encrusted that solar energy had slowed to a drop.

Thereafter, Martian Mother Nature made an entry, giving Opportunity a wonderfully timed and much required ‘cleaning event’. On the surface of Mars cleaning events have become a vital, but unplanned component of long-duration solar powered missions.

Both Opportunity and sister rover Spirit have witnessed Martian winds and dust devils that have driven away the rovers, eradicating some of the dusty layer, providing them a powerful boost.

The latest cleaning event of Opportunity has occurred toward the end of last year, before it plunged into Martian winter, which allowed the rover to carry forward its valuable work into this year.

In a NASA news update, Mars Exploration Rover Project Manager John Callas, of NASA’s Jet Propulsion Laboratory, Pasadena, Calif, said, “Opportunity has stayed very active this winter, in part because the solar arrays have been much cleaner than in the past few winters”.