The Case for Alien Life

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.

Curiosity found in the ancient clay many of the elements needed for life: carbon, hydrogen, oxygen, nitrogen, and phosphorus. We don't know whether bacteria, let alone Earth-like plants and animals, once teemed in Yellowknife Bay, but they could have. The rover was just the newest scout in humanity's decades-long exploration of Mars, an effort that currently includes the dogged 10-year-old Opportunity rover and three orbiters in space. But Yellowknife Bay is the first site ever observed, on Mars or anywhere else, that clearly could have supported extraterrestrial life.

Generations of scientists and science-fiction fans (often, those are the same people) have thought we'd find life strewn throughout the stars?if not civilizations, at least bacterial mats, or tentacled beasts on ocean floors, or something. But for decades the evidence was thin. Now, in 2013, the data is on the side of the believers. It has been provided by increasingly sophisticated probes, space telescopes, and rovers. Planets were once thought to be rare; by the time the Kepler space telescope ran into severe mechanical problems in May, it had proved that alien worlds actually number in the billions. Scientists imagined the universe to be parched; new studies show that it's filled with watery planets. And, surprise: Life isn't some delicate thing, like a pasty tourist stuck beneath a beach umbrella; it's now known to be more like a hardy soldier, able to infiltrate the harshest environments.

The exciting exobiological news keeps coming: In April, astronomers identified a trio of planets that appear capable of supporting Earth-like life. They orbit their stars' habitable zones, the just-right distance where water neither freezes nor boils, but collects in sloshy, life-friendly oceans. One of the worlds, dubbed Kepler-62e, even shows signs of a humid atmosphere strewn with clouds. More such discoveries will come.

Louisa Preston, an astrobiologist at Open University in the U.K., investigates the telltale signs of biology that could help us locate life in space. "It's now predicted that there are 17 billion Earth-like planets in our galaxy alone," Preston says. "And since our galaxy is one of hundreds of billions in the universe, the chances of finding life are increasing exponentially." Here are three reasons, in detail and based on current research, why we are much more likely to find life than to discover we are alone.

Source: http://www.popularmechanics.com/science/space/deep/the-case-for-alien-life-15756398?src=rss

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