[meteorite-list] First Detection of Organic Molecules in Extrasolar Planetary Atmosphere

From: Sterling K. Webb <sterling_k_webb_at_meteoritecentral.com>
Date: Wed, 19 Mar 2008 15:45:08 -0500
Message-ID: <3e0301c88a02$1eeb1670$1247e146_at_ATARIENGINE>

http://www.telegraph.co.uk/earth/main.jhtml?xml=/earth/2008/03/19/scialien119.xml

Milestone in hunt for extraterrestrial life
By Roger Highfield, Science Editor

Astronomers have found organic chemicals on
a planet outside our solar system for the
first time, a milestone in the hunt for
extraterrestrial life.

Researchers also identified water in the
searing hot atmosphere of the alien planet,
which orbits a distant star more than 60
light years away.

Roger Highfield explains the significance of
the discovery of methane on the alien planet
The planet is too close to its parent star and
so is too hot for conditions to be favourable
for life as we understand it.

But the ability of scientists to analyse its
atmosphere and detect simple carbon-based
molecules is a crucial step in efforts to
find planets which may harbour extraterrestrial
life.

The feat is reported today in Nature with possibly
the best understood alien planet of all the 270
detected so far, called HD 189733b, which was
discovered in 2005 in the constellation Vulpecula.

The achievement demonstrates the ability to detect
organic molecules in "Goldilocks zones" around
planets, so named because they are just right
for liquid water to be present.

The planet - of a type often referred to as a
'hot Jupiter' - is like our own Jupiter, made of
gas, but orbits much closer to its sun.

The reason we know so much about this alien world
is that, seen from our own Earth, it transits its
star, passing in front of it during each
2.2-day-long orbit. As the light from the parent
star passes through the atmosphere around the
limb of the giant extrasolar planet, the gases
in the atmosphere stamp their unique signature
on the starlight from HD 189733.

By using spectroscopy, which splits light into its
components, scientists can see the "fingerprints"
of various chemicals.

Previous studies have predicted that methane and
water would be present in the atmosphere, just
like on Jupiter, but until now no definitive evidence
has been found.

Using light analysed by the Hubble Space Telescope,
Dr Mark Swain of the Jet Propulsion Laboratory and
the California Institute of Technology, Pasadena,
and colleagues confirm the presence of methane.
They also report in the journal Nature they have
found the signature of water, but carbon monoxide,
originally expected to be abundant in the upper
atmosphere, was not identifiable.

"I am excited about our observations of methane
because they represent a "dress rehearsal" for
our ultimate goal of studying organic molecules
on planets where life might exist," he tells the
Telegraph. "With this observation there is no
question whether there is water or not -- water
is present", he adds.

"These measurements are an important step to
our ultimate goal of determining the conditions,
such as temperature, pressure, winds, clouds,
and so on, and the chemistry on planets where
life could exist."

Team member Dr Giovanna Tinetti from the University
College London adds: "We haven't found life on
another planet yet, but this in an exciting step
towards showing that we can detect these signature
molecules."

On Earth, methane is produced by a variety of sources:
natural sources such as termites, the oceans and wetland
environments, but also from cows, livestock and manmade
sources like waste landfills and as a by-product of
energy generation. But she adds: "The planet's atmosphere
is far too hot for even the hardiest life to survive -
at least the kind of life we know from Earth. It's highly
unlikely that cows could survive here!"

Prof Adam Showman of the University of Arizona, Tucson,
says that despite its low abundance, the methane provides
telling clues about planetary formation, evolution, weather,
photochemistry and - in the case of Earth where oxygen
is also present - life.

"These are exciting times for studies of extrasolar planets.
Thirteen years after the discovery of the first extrasolar
planet around a Sun-like star, we are finally moving beyond
simply discovering such planets to truly characterising
them as worlds."

Considered suggestive of life, methane can also be made
by non-biological processes. However, under the right
circumstances methane can play a key role in prebiotic
chemistry - the chemical reactions considered necessary
to form life as we know it.

The father of Gaia theory, the independent British scientist
James Lovelock proposed that the simultaneous presence of
oxygen and methane would be a convincing indication of life.

The reason that it is a "biosignature" is that methane is
turned by oxygen into carbon dioxide, so the fact that
methane is seen on Earth means that the methane is
continually produced, by bacteria in the guts of humans
for example.

But there is no sign of oxygen on this alien world. Unless
molecular oxygen is constantly replenished by photosynthesis,
it is quickly consumed in chemical reactions, in the
atmosphere, on land and in seawater.

So the presence of a large amount of oxygen in an extrasolar
planet's atmosphere would be a sign that it might host an
ecosystem like Earth's, where cyanobacteria did not start
starting cranking out oxygen until around 2.5 billion years
ago and it was not until about 600 million years ago when
the atmospheric oxygen level rose to a fraction of modern
levels.

The HD 189733b planet, orbiting close to its parent star,
has an atmospheric temperature of roughly 700?C. Measurements
of the way light varies as the planet passes in front of
its parent star indicates that HD 189733b has neither
Earth-sized moons nor any discernable Saturn-like ring system.

Like most planets that are very close to their parent
stars, HD 189733b has one side always facing its star
in perpetual daytime while the other is permanently dark.
The cooler, night side of HD 189733b faces us when the
planet is in front of its star and the hotter day side
rotates into view just before the planet disappears
behind its host.

Earlier work suggests that it is a sweltering 940?C on
the day side, and even the permanently dark side is a
surprisingly hot 700 ?C in the upper atmosphere, probably
because powerful winds whip round the globe at about
eight times the speed of sound on Earth, spreading out
the heat. In the lower atmosphere, temperatures are
even higher.
Received on Wed 19 Mar 2008 04:45:08 PM PDT


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