[FPSPACE] Fw: ESA: Was Venus Once a Habitable Planet?
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Thu Jun 24 08:18:37 EDT 2010
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From: "AAS Press Officer Dr. Rick Fienberg" <rick.fienberg at aas.org>
Date: Thu, 24 Jun 2010 11:54:50
To: <Rick.Fienberg at aas.org>
Subject: ESA: Was Venus Once a Habitable Planet?
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24 June 2010
Article and images:
WAS VENUS ONCE A HABITABLE PLANET?
ESA's Venus Express is helping planetary scientists investigate
whether Venus once had oceans. If it did, it may even have begun its
existence as a habitable planet similar to Earth.
These days, Earth and Venus seem completely different. Earth is a
lush, clement world teeming with life, whilst Venus is hellish, its
surface roasting at temperatures higher than those of a kitchen oven.
But underneath it all the two planets share a number of striking
similarities. They are nearly identical in size and now, thanks to
ESA's Venus Express orbiter, planetary scientists are seeing other
"The basic composition of Venus and Earth is very similar," says Hakan
Svedhem, ESA Venus Express Project Scientist. Just how similar
planetary scientists from around the world will be discussing in
Aussois, France, where they are gathering this week for a conference.
One difference stands out: Venus has very little water. Were the
contents of Earth's oceans to be spread evenly across the world, they
would create a layer 3 km deep. If you were to condense the amount of
water vapor in Venus's atmosphere onto its surface, it would create a
global puddle just 3 cm deep.
Yet there is another similarity here. Billions of years ago, Venus
probably had much more water. Venus Express has certainly confirmed
that the planet has lost a large quantity of water into space.
It happens because ultraviolet radiation from the Sun streams into
Venus's atmosphere and breaks up the water molecules into atoms: two
hydrogens and one oxygen. These then escape to space.
Venus Express has measured the rate of this escape and confirmed that
roughly twice as much hydrogen is escaping as oxygen. It is therefore
believed that water is the source of these escaping ions. It has also
shown that a heavy form of hydrogen, called deuterium, is
progressively enriched in the upper echelons of Venus's atmosphere,
because the heavier hydrogen will find it less easy to escape the
"Everything points to there being large amounts of water on Venus in
the past," says Colin Wilson, Oxford University, UK. But that does not
necessarily mean there were oceans on the planet's surface.
Eric Chassefiere, Universite Paris-Sud, France, has developed a
computer model that suggests the water was largely atmospheric and
existed only during the very earliest times, when the surface of the
planet was completely molten. As the water molecules were broken into
atoms by sunlight and escaped into space, the subsequent drop in
temperature probably triggered the solidification of the surface. In
other words: no oceans.
Although it is difficult to test this hypothesis it is a key question.
If Venus ever did possess surface water, the planet may possibly have
had an early habitable phase.
Even if true, Chassefiere's model does not preclude the chance that
colliding comets brought additional water to Venus after the surface
crystallized, and these created bodies of standing water in which life
may have been able to form.
There are many open questions. "Much more extensive modeling of the
magma ocean-atmosphere system and of its evolution is required to
better understand the evolution of the young Venus," says Chassefiere.
When creating those computer models, the data provided by Venus
Express will prove crucial.
ESA PIO Source:
ESA Communication and Knowledge Department
+31 71 56 56799
markus.bauer at esa.int
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