- An international space probe will launch Thursday morning
to take the closest look yet at the core of a comet, and may shed light
on the origin of life on Earth.
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- A series of recent studies have suggested that comets
may have brought water and amino acids -- the building blocks of life --
to Earth billions of years ago. But that's all theoretical. Scientists
don't yet have direct proof that comets really carry these materials. Only
a couple of probes have ever seen comets up close.
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- Rosetta, the European Space Agency craft scheduled to
lift off Thursday from a launching pad in French Guyana, could dramatically
augment the available evidence. If it works as planned, Rosetta will be
the first probe to land on a comet's surface. The samples it takes from
the soil and atmosphere of comet 67P/Churyumov-Gerasimenko should determine
whether these interplanetary streakers contain the chemical precursors
to bacteria, plants and people.
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- "One of the fundamental outstanding questions about
comets is, 'Do they contribute to life in the solar system?'" said
Claudia Alexander, a project scientist at NASA's Jet Propulsion Laboratory.
She's overseeing NASA's contribution to the Rosetta mission -- three sensors
to look for organic matter, among other things. "Comets may be the
seeds from which life may have come."
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- Interplanetary dust particles carrying 300 tons of organic
material hit the Earth annually, said William Irvine, an astronomy professor
at the University of Massachusetts at Amherst. That may seem like a lot,
but it's a drizzle compared with the hailstorm 4.5 billion years ago when
the planet was young. Earth then was endlessly bombarded with asteroids
and comets, without much of an atmosphere to protect the planet.
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- Scientists know that at least some of these rocks contained
amino acids, said Michael Mumma, director of astrobiology at NASA's Goddard
Space Flight Center. Some meteors found largely unchanged from that period
-- like the so-called "Orgueil meteorite" -- contain traces of
at least two different amino acids. Others have been found with up to 70
of the molecules.
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- This influx of amino acids, and likely water, before
life began on Earth has lead some researchers to believe that these interplanetary
visitors might have helped spawn life here. Other scientists take a more
traditional view, theorizing that some sort of electrical discharge must
have struck the planet's primordial soup, giving rise to living things.
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- Findng amino acids on Churyumov-Gerasimenko won't settle
this dispute. But it will bolster the case that life here may have received
an alien push to start.
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- The Rosetta mission will do more than look at life-on-Earth
issues, however. It's also supposed to provide insights into how the solar
system itself was created.
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- The evolutionary history of comets has preserved their
matter exactly as they were before the sun began to burn, Gerhard Schwehm,
ESA's planetary science chief, said on the space agency's website. So looking
at comet Churyumov-Gerasimenko is like looking at an icy artifact from
the solar system's most primitive proto-history.
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- But getting there won't be easy. Recent mishaps with
probes to Mars have shown how tricky orbiting and landing on another planet
can be. And while the comet doesn't have the relatively thick atmosphere
and heavy gravitational pull of Mars, rendezvousing with a comet has its
own set of quirks.
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- Already, the mission had been delayed a year after an
Arianne-5 rocket (the probe's launch vehicle) failed. That caused the ESA
to change Rosetta's dance partner, comet 46P/Wirtanen, to a rock with a
different size and shape.
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- To gain enough speed to be able to make it to its new
destination, the 3-ton Rosetta probe will have to do a cosmic loop the
loop -- circling the Earth three times, and Mars once, to build up the
velocity for its comet encounter. Once Rosetta gets there, nobody's sure
what it will find. As Schwehm notes, scientists are half guessing what
the comet's shape and surface will be like.
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- "We'll have to learn a lot when we get there --
spin, axis, rotation period -- to get (Rosetta) into the proper orbit,"
he said. To give it time to make the calculations, Rosetta will start braking
about four months before it gets to Churyumov-Gerasimenko, slowing its
kilometer-per-second speed tenfold.
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- Once it starts circling the comet's 4-kilometer nucleus,
Rosetta will have about three months to figure out how to gets its cube-shaped,
100-kilogram lander onto the surface. The key is to be gentle. Because
the comet has very little gravitational pull, the lander could just "bounce
off and disappear" if it comes down too hard, Schwehm said. "The
impact will be less than a meter per second. That's like if you walk fast,
and hit a wall."
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- To make sure that even that tiny contact doesn't send
the lander reeling, it will fire a harpoon into the surface to anchor itself.
Then, the lander will deploy acoustic, X-ray and electrical sensors --
complementing the orbiter's ultraviolet, infrared and microwave instruments.
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- And the hunt for life's essential elements will be under
way.
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