Mars: Pop. 6

No gridlock yet, but traffic on the Red Planet is getting heavier

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NASA / JPL / Caltech

Never mind the image of Mars as a dead and desolate world. The Red Planet has lately become one of the busiest little places in the solar system.

The past decade has been something of a Martian era of space exploration. Since 1996, the U.S. alone has launched no fewer than nine spacecraft Marsward, and seven have arrived in one piece--an extraordinary success rate for a planet that historically had been a bit of a graveyard of failed missions. Currently, six ships--five American and one European--are at work on Mars, and a handful of others sleep peacefully on the surface or orbit silently above, their missions completed and their systems exhausted. While a lot of the work the spacecraft do is the quiet business of spelunking and air-sampling that thrills mostly space geeks, in recent weeks the news from Mars has been compelling.

On Sept. 29, NASA announced that a laser instrument aboard the Phoenix lander, which touched down north of Mars' arctic circle last May, had spotted snow falling through the planet's frigid sky. Martian snowfall isn't like earthly snowfall; this descended from some 2.4 miles (4 km) up and appeared to vaporize before it reached the surface. Still, the picture that Phoenix is painting is of a meteorologically dynamic world, one not only with occasional flurries but also with clouds and fog forming at night in addition to the famed Martian winds.

Two 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.

But 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.

Earlier in September, NASA announced that Opportunity would wander farther than it ever had in the search for more data. The rover is embarking on a long trek to a crater roughly 7 miles (12 km) away. That's about the total amount of ground it has covered since it arrived. Even if it follows a beeline route, its slow speed and the starts and stops it must make along the way limit it to about 110 yd. (100 m) per day--meaning it will need two years to get where it's going. Still, the trip should be easier than it once would have been, thanks to a sister ship, the Mars Reconnaissance Orbiter, which arrived in 2006 and can provide eye-in-the-sky guidance.

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