Spacewatch: A decade of Opportunity on Mars

eploration rover on surface of mars
An artist's impression of a Mars Exploration Rover on the surface of Mars, where it functions as a robotic geologist. Photograph: Nasa

Saturday marks the 10th anniversary of the landing of Nasa's Opportunity rover on Mars. Cocooned in air bags, it bounced to a halt on the Martian surface at 05:05 GMT, three weeks after its twin, Spirit.

What was initially a project to land a single golf-cart-sized rover, dubbed the Mars Exploration Rover, had evolved quickly into a two-rover mission in the face of scepticism about a single craft's prospect of success. After all, the majority of previous Mars missions had ended in failure, embarrassingly so for Nasa's Mars Polar Lander and Mars Climate Orbiter in 1999.

With the rovers assigned primary missions lasting only 90 days, it is astounding that Opportunity is still operating, while Spirit functioned for five years before becoming bogged down in a Martian sandpit (it last spoke to Earth in 2010).

Luck has played its part. The power yielded by their solar arrays fell, as expected, as they became coated in wind-blown dust. What was unexpected was that the arrays would be swept and their efficiency restored by dust devils dancing across the Martian plains.

Both rovers have amply fulfilled their briefs to "follow the water", discovering rock formations and minerals that confirm Mars was once a wet world. Spirit had driven for 7.7km before its demise, while Opportunity has trundled for 38km to the 22km-wide Endeavour crater. Here, aided by dust-clearing gusts, and with its solar arrays tipped northwards, it expects to survive the midwinter at its southern hemisphere vantage point on the crater's rim.