The Mystery of the Green Interloper -Did Comets Deliver the Building Blocks for Life?

Ags1 (1) A pale green interloper among the stars of Cassiopeia, Comet Hartley 2 glows like an escapee from Krypton at the center of this exposure. In 2007 the comet became the primary target for a NASA spacecraft called Deep Impact. That probe's first mission had been to launch a projectile into comet Temple 1 in 2005, kicking up a plume of ice and dust so that astronomers could study the comet's composition.  After that mission ended, the Deep Impact "mothership" still had enough fuel for followup experiments, so NASA redirected the probe for an encounter with comet Hartley 2.

Now called EPOXI, for Extrasolar Planet Observation and Deep Impact Extended Investigation, the spacecraft is closing in on Hartley 2 and is due to make a flyby on November 4. The craft will dive within 600 miles (965 kilometers) of the comet's surface, getting close-up images of its craters and sources of dust and gas plumes.

Based on the large differences seen between previous comets visited by robotic probes—including comets Halley, Wild 2, Borrelly, and Temple 1. "The mission may answer whether comet Hartley 2 has a family resemblance to one of these, or if it is also unique," said Anthony Cook, an astronomer at the Griffith Observatory in California . "Its composition is also of interest, as it is suspected that at least some comets may have formed outside of the solar system."

Comet 103P/Hartley 2, a small periodic comet, was discovered in 1986 by Malcolm Hartley, an Australian astronomer. It orbits the sun about every 6.5 years, and on Oct. 20, the comet will make its closest approach to Earth since its discovery. In this case, "close" means 11 million miles, or 17.7 million kilometers. A moonless sky will make for promising viewing conditions in the northeastern skies, especially just before dawn.

The fact that life appeared soon after the termination of the heavy bombardment about 3.8 billion years ago suggests that it seems reasonable that incoming comets and asteroids delivered the compounds essential for life.

The 2005 Deep Impact mission to Comet Tempel 1 discovered a mixture of organic and clay particles inside the comet that show it is overwhelmingly likely that life began in space, according to resaerch by Cardiff University scientists, professor Chandra Wickramasinghe and colleagues at the University’s Center for Astrobiology.

One theory for the origins of life proposes that clay particles acted as a catalyst, converting simple organic molecules into more complex structures. The 2004 Stardust Mission to Comet Wild 2 found a range of complex hydrocarbon molecules – potential building blocks for life.

The Cardiff team proposes the controversial theory that radioactive elements can keep water in liquid form in comet interiors for millions of years, making them potentially ideal “incubators” for early life. They also point out that the billions of comets in our solar system and across the galaxy contain far more clay than the early Earth did. The researchers calculate the odds of life starting on Earth rather than inside a comet at one trillion trillion (10 to the power of 24) to one against.

Professor Wickramasinghe said: “The findings of the comet missions, which surprised many, strengthen the argument for panspermia. We now have a mechanism for how it could have happened. All the necessary elements – clay, organic molecules and water – are there. The longer time scale and the greater mass of comets make it overwhelmingly more likely that life began in space than on earth.”

In his essay, Extraterrestrials: A Modern View, University of Washington professor Guillermo Gonzalez wrote: "The kind of origin of life theory a scientist holds seems to depend on his/her field of specialty: oceanographers like to think it began in a deep sea thermal vent, biochemists like Stanley Miller prefer a warm tidal pool on the Earth's surface, astronomers insist that comets played an essential role by delivering complex molecules, and scientists who write science fiction part time imagine that the Earth was "seeded" by interstellar microbes."

Posted by Casey Kazan via Cardiff University
Comet probes reveal evidence of origin of life, scientists claim
Casey Kazan via National Geographic and http://nssphoenix.wordpress.com/2010/07/01/comet-hartley-2/

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