The spacecraft that explore the solar system are built tough. They have to travel millions of miles, survive extreme heat and cold and deadly radiation, and operate with little help from home.
Even by those standards, though, the Mars Exploration Rovers are remarkable machines. They landed on Mars five years ago this month with identical missions: explore the dusty landscape for three months. And although engineers expected the golfcart-sized rovers to keep going longer than that, few expected them to last as long as they have: as of late last year, both were still going.
The Spirit rover landed inside Gusev crater, and traveled a couple of miles to a small range of hills. It's found evidence that the rock layers formed in a wet environment, confirming that Mars was warmer and wetter in the distant past.
The other rover, Opportunity, landed in the Martian plains. It spent months exploring a small crater, then a year inside a larger one. It, too, found evidence of a watery past -- although much of the water was acidic, making it not very hospitable for life.
Both rovers are showing signs of their age. Some of their wheels don't work, and some of their instruments and tools have failed. And dust covers their solar panels, so they don't produce as much power.
Yet their adventures may continue. Opportunity has embarked on a seven-mile drive to a giant crater -- a road trip that could take two years. More about that tomorrow.
Script by Damond Benningfield, Copyright 2008
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