Washington, Dec 30 : NASA rovers Spirit and Opportunity are all set complete the fifth anniversaries of their memorable landings on Mars in January 2009.

While Spirit had landed safely on Mars on January 3, 2004, Opportunity touched down on the surface of the Red Planet 21 days later.

"The American taxpayer was told three months for each rover was the prime mission plan," said Ed Weiler, associate administrator for NASA's Science Mission Directorate at NASA Headquarters in Washington.

"The twins have worked almost 20 times that long. That's an extraordinary return of investment in these challenging budgetary times," he added.

The rovers have made important discoveries about wet and violent environments on ancient Mars.

They also have returned a quarter-million images, driven more than 13 miles, climbed a mountain, descended into craters, struggled with sand traps and aging hardware, survived dust storms, and relayed more than 36 gigabytes of data via NASA's Mars Odyssey orbiter.

To date, the rovers remain operational for new campaigns the team has planned for them.

"These rovers are incredibly resilient considering the extreme environment the hardware experiences every day," said John Callas, JPL project manager for Spirit and Opportunity.

"We realize that a major rover component on either vehicle could fail at any time and end a mission with no advance notice, but on the other hand, we could accomplish the equivalent duration of four more prime missions on each rover in the year ahead," he added.

With Spirit's energy rising for spring and summer, the team plans to drive the rover to a pair of destinations about 200 yards south of the site where Spirit spent most of 2008.

One is a mound that might yield support for an interpretation that a plateau Spirit has studied since 2006, called Home Plate, is a remnant of a once more-extensive sheet of explosive volcanic material. The other destination is a house-size pit called Goddard.

For Opportunity, the next major destination is Endeavour Crater.

It is approximately 14 miles in diameter, more than 20 times larger than another impact crater, Victoria, where Opportunity spent most of the past two years. (ANI)