- There could be life on the planet Venus, US scientists
have concluded in a report in the journal Astrobiology.
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- The existence of life on the planet's oven-hot surface
is unimaginable.
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- But microbes could survive and reproduce, experts say,
floating in the thick, cloudy atmosphere, protected by a sunscreen of sulphur
compounds.
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- Scientists have even submitted a proposal for a Nasa
space mission to sample the clouds and attempt to return any presumed Venusians
to Earth.
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- "Venus is really a hellish place," said Professor
Andrew Ingersoll, of the California Institute of Technology.
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- "If you could get through the sulphuric acid clouds
down to the surface of Venus you'd find it was hotter than an oven. You
could melt lead at the surface of Venus and there'd be no water."
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- But it was not always like that. Earth and Venus are
in many ways sister planets.
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- "Current theories suggest that Venus and the Earth
may have started out alike. There might have been a lot of water on Venus
and there might have been a lot of carbon dioxide on Earth," Professor
Ingersoll explained.
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- But all that was to change. On Earth, life in the oceans
took in carbon dioxide and turned it into limestone. On Venus, 30% closer
to the Sun, any oceans boiled away and the water vapour added to the runaway
greenhouse effect.
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- Venus became our planet's ugly sister. Its make-over,
which occurred billions of years ago, has left a surface where the pressure
is crushing.
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- Arrested development
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- But, according to Louis Irwin of the University of Texas
at El Paso, the changes on Venus may have been slow. "It may well
have been Earth-like long enough for life to either emerge or be transported
there," he said.
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- Once established, life would have adapted to every environment,
just as it did on Earth.
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- Two years ago, Austrian scientists discovered bacteria
living and reproducing within clouds on Earth. The same could have been
true on Venus. Then, as the surface became hot and dry, the clouds might
have become life's only refuge.
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- The Venusian clouds are high in the atmosphere, where
the temperature and pressure are quite Earth-like. There is even water
present, though it is in the form of concentrated sulphuric acid.
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- But we now know of organisms that thrive in very acidic
environments on Earth.
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- "If you think about what life needs in a broad sense
then the clouds of Venus might actually be a habitat where something could
live," explained David Grinspoon, of the South West Research Institute
in Colorado.
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- Another problem could be UV radiation from the Sun. But
Dirk Shulze-Makuch, also at El Paso, thinks Venusian bacteria could make
use of a natural chemical sunscreen there.
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- "When we looked at the composition of the atmosphere,
we thought that sulphur compounds are actually an ideal sun block for microbes."
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- David Grinspoon speculates that the organisms might even
have evolved ways of making use of the UV, much like Earth plants use visible
light for photosynthesis.
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- "One lifeform's deadly radiation may be another
lifeform's lunch," he added.
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- But will we ever know if there is truth behind the speculation?
Louis Irwin and his colleagues have a proposal in with the US space agency,
Nasa.
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- "We would send a probe to Venus that would drop
probably a collector tethered to a balloon-like floating spacecraft, it
would collect samples of the cloud droplets and then blast off from the
Venusian atmosphere for return eventually to Earth."
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- And what are the chances of finding live Venusians? David
Grinspoon is in no doubt: "If they're there, I think we will find
them eventually."
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- © BBC MMIV
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- http://news.bbc.co.uk/1/hi/sci/tech/3746583.stm
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