Word: martian
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...left them silent and still, but only until conditions improved and they shook off the dust, stirred to life and puttered off to do more work. So far, Spirit and Opportunity have beamed home a quarter of a million images and 36 gigabytes of data and revealed more about Martian history than any other spacecraft in a half-century of space travel. And by all indications, they could be keeping it up for a long time to come...
...long Sojourner craft, which arrived on Mars in the summer of 1997. Like its bigger siblings, Sojourner came with only a very brief factory warranty - just 30 days in its case - and like its bigger siblings, easily exceeded it, operating for five months before finally surrendering to the Martian elements. It's rarely a good idea to take NASA's estimates of the lifespan of its ships too literally. The agency tends to lowball these calls, making it more likely that the machines will perform better than advertised - and, not incidentally, that taxpayers will feel as though they're getting...
Spirit and Opportunity did just that, aiming for vast basins that have the look of land that was once submerged. Spirit soon uncovered evidence of salts in the soil, a substance that would have been abundant in Martian seas, just as it is in Earth's. Opportunity discovered deposits of BB-sized pellets - which NASA nicknamed blueberries - that are rich in hematite, a mineral that forms only in watery environments. And by pure serendipity, in 2007 a balky wheel on Spirit dug a shallow trench in the ground, revealing the presence of white silica, another indicator of water...
...seemingly indestructible Martian rovers have also been busy. Since landing in early 2004, the golf-cart-size Spirit and Opportunity have toddled about on different parts of the planet, dipping into craters, drilling into rocks and sending back data about Mars' makeup and watery past. But the Martian elements have left the rovers increasingly arthritic: Opportunity's robotic arm has stiffened to the point that controllers no longer retract it fully, and Spirit has been forced to drive backward as a result of a bum front wheel...
...even breakdowns can pay dividends. In May 2007, scientists announced the discovery of white silica beneath the Martian soil--a telltale mineral that usually forms in the presence of water--one more bit of proof that Mars was once a wet place. The silica would never have been discovered if Spirit's balky wheel hadn't dug a trench in the soil...