When it comes to Mars missions, NASA's twin rovers Spirit and Opportunity seem to be the robots that never quit. The two plucky probes were each built for a 90-day romp across the Martian surface, a mission that began when Spirit bounced to a stop on the planet's expansive Gusev Crater five years ago today. Opportunity touched down on the other side of Mars a few weeks later and now - after half a decade - both rovers are still exploring the red planet after surviving more than 20 times their planned lifetime. "The American taxpayer was told three months for each rover was the prime mission plan," said Ed Weiler, NASA's associate administrator for science missions at the agency's Washington, D.C., headquarters, in a statement. "The twins have worked almost 20 times that long. That's an extraordinary return of investment in these challenging budgetary times." The rovers reportedly cost about $20 million to operate each year since their 2004 arrivals on Mars. Roving Mars Spirit set down at Gusev Crater on Jan. 3 at 11:35 p.m. EST (8:35 p.m. PST), where it overcame initial computer glitches and went on to scale nearby hills and brave the frigid Martian winter



year after year. Opportunity bounced to a stop inside what scientists later dubbed Eagle crater just after midnight (EST) Jan. 25 in an interplanetary hole-in-one on the vast Martian plains of Meridiani Planum. Since then, the rover has spotted a Martian meteorite, visited the heat shield cast off during its landing and explored ever larger craters as it makes it way toward Endeavour, a monster crater 14 miles (22 km) across.