Friday, August 2, 2013

The Case for Alien Life

Only one planet has been proven to support life: our own. But with at least 11 billion Earth-sized words in our galaxy orbiting in their stars' habitable zones, plus new evidence of strange kinds of life that thrive in extreme environments, the odds that we are not alone are improving.


On Feb. 9, 2013, NASA's Curiosity rover found something on Mars that set a milestone in the search for alien life. Packed with instruments, the rover was an SUV-size speck crawling across the floor of the Gale Crater, whose distant walls climbed 15,000 feet in the thin air. The rover had been lowered to the ground six months earlier by means of a complex, jet-propelled sky crane. Now, almost 221 million miles from home but just a quarter-mile from its landing site, Curiosity was exploring a shallow depression called Yellowknife Bay. The machine trundled up to an outcropping of bedrock, which lay dry and cracked beneath a yellow sky. It drilled into the rock and within minutes pulled a fine gray powder from the narrow borehole. Curiosity scooped up the dust and tasted it.

The sample contained smectite clay, which on Earth is found in alluvial plains and regions washed by monsoons. Today, Mars is a largely arid world whipped by global dust storms, where temperatures can swing 170 F in a day. Three billion years ago, it seems, a river of sweet water cascaded over the rim of Gale Crater and emptied into a lake in Yellowknife Bay. The sky was probably bluer then, and cloudier, and the terrain hadn't yet rusted from gray to red. Mount Sharp, which rises 18,000 feet above the crater floor, may have been capped in ice and snow.

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