The Rovers Are Still Exploring Mars After Two years

The NASA scientists didn't believe the rovers would resist more than three months in Mars' harsh environment. Nonetheless, two years later there are still marching on and they are still sending information. So far they have traveled more than 11 kilometers and they have sent more than 100 000 photographs.

The rover Spirit landed on Mars on January 3, 2004, and Opportunity followed on January 24. Spirit has traveled almost 5 kilometers and has sent 70 000 images so far, and Opportunity has traveled more than 6 kilometers and has sent 58 000 images. One of the reasons the rovers are still working is pure luck: the 160 km/h dust devils they encountered, instead of destroying them, helped them by blowing away the sand that had started to cover their solar panels.

The two rovers were sent to find whether Mars had ever had liquid water � this being a necessary condition for life. The two probes were parachuted on opposite ends of Mars, Spirit in a huge crater almost 150 kilometers wide south of the Equator (the Gusev crater), and Opportunity in a plain called the Meridiani Planum on the other side of the planet.
The scientists were attracted by Gusev crater because it looks like there's a channel system that drains into it, which probably carried liquid water, or water and ice, into the crater. �It's hard to imagine the landscape looking this way unless water was somehow involved,� said Jim Garvin, NASA's Lead Scientist for Mars Exploration.
On the other hand, Meridiani Planum attracted the researchers because it contains an ancient layer of hematite, an iron oxide that, on Earth, almost always forms in an environment containing liquid water. Meridiani Planum is also attractive because the site appears to be eroding, with once-buried craters that are now half-revealed.

Both rovers have found certain traces which NASA scientists consider revealing evidences for the past existence of liquid water. All these evidences are circumstantial, in the sense that if liquid water ever existed on Mars it would have left behind such traces. The first rover to find evidences of liquid water was Opportunity which had the luck of landing near some salt sediment. Examples of the type of evidences Opportunity has found are here, here and here.

Among Spirit's adventures one can count the escalation of a hill as tall as the Statue of Liberty. The scientists were afraid it wouldn't survive the climb due to the harsh weather, but the rover has surpassed the hill and now is heading towards a basin that looks geologically interesting.

In their two year journey so far the rovers had a number of difficulties but they were solved by the NASA scientists. At one point, Spirit had a balky front wheel, but engineers overcame the problem by driving it in reverse. Last spring, Opportunity got stuck hub-deep in sand while trying to crest a 30 centimeters-high dune, and was freed after weeks of effort by the Earth-bound engineers. In November, a motor on Opportunity's robotic arm stalled and the arm failed to extend while it was surveying a rock outcrop. The engineers fixed that problem after two weeks.

Right now Opportunity is rolling to an enormous depression known as Victoria Crater that is thought to hold more clues about the planet's past.