Climate and Evolution of Venus (Forwarded)

ESA News
http://www.esa.int

28 November 2007

Climate and Evolution

Today, Venus is a hellish place of high temperatures and crushing air
pressure. Venus Express is showing that this was not always the case.
Instead, some time in the past, Venus was probably much more Earth-like and
contained large quantities of water.

Planetary scientists have long wondered just how Earth-like Venus is or
might have been. Until the 1960s, astronomers speculated that Venus might be
a tropical forest planet. This view changed when microwave observations
began to suggest an extremely hot surface. The Russian and American
spacecraft of the 1960s and 70s confirmed that Venus possesses surface
temperatures of over 400 C and surface pressure a hundred times that of
Earth.

The winds in Venus' atmosphere are severe, blowing at speeds of up to, and
over, a 100 m/s. Yet, as fierce as they are, not even the winds from the
giant south polar vortex extend all the way down to the planet's surface.

Venus Express can see down to about 45-50 km above the surface in the south
polar region. Feeding this data into computer models suggests that the
vortex cannot penetrate into the lower atmosphere because of the great
density of gas there. "It is difficult to move around such a heavy mass of
atmosphere. We do not expect big winds at the surface of Venus," says
Giuseppe Piccioni, IASF-Istituto Nazionale di Astrofisica, Italy.

How did Venus turn out like this?

Geologists say that the present is a clue to the past and the same is true
for atmospheric physics. Venus Express has revealed an atmospheric process
that points to a catastrophic event in Venus' history.

"Venus has suffered a radical climate disaster but we don't yet know how,
why and when," says David Grinspoon, a Venus Express interdisciplinary
scientist from the Denver Museum of Nature and Science, Colorado, USA.

The disaster was the loss of Venus' water. If you could condense all of the
water vapour in Venus' atmosphere, it would create a thin covering of water
just 3-cm thick. For comparison, if Earth were a smooth ball, all of the
water in the oceans and atmosphere would create a covering 3-km deep.

Venus may once have had this much water as well but it has been gradually
stripped off into space by the collision of energetic particles from the
Sun. Today, Venus Express has shown that the last remnants of the process
are still taking place with the escape of hydrogen and oxygen from the top
of the atmosphere.

"We now know that Venus was once more Earth-like," says Grinspoon, "We
cannot tell the full story yet, but the data we are getting shows that Venus
Express will reveal the history of water on Venus.

Venus has no seasons because its rotation axis is already perpendicular to
its orbit. It rotates just once in 243 Earth days and has a very massive
atmosphere. This is chiefly composed of carbon dioxide with clouds primarily
of sulphuric acid droplets.

It sounds nothing like Earth, and yet, thanks to Venus Express, planetary
scientists now know that it can be explained in the same framework, but with
Venus being driven in a different direction.

"The three most important parameters that determine a planet's 'behaviour'
are its distance from the Sun, its surface pressure and its rotation rate,"
says Fred Taylor, a Venus Express interdisciplinary scientist from the
University of Oxford, UK. So, although Venus is similar in size to Earth, it
is drastically different in the three parameters that drive its behaviour.

There is another large unknown in the evolution of the atmosphe the
amount of lightning on the planet. Lightning drives the chemistry of an
atmosphere by breaking molecules into fragments that can then join other
fragments in unexpected ways. Nitric oxide formed in this manner is present
in sufficient quantities to be detected from Earth.

"There may be as much lightning on Venus as there is on Earth," says Chris
Russell at the University of California at Los Angeles, who was part of the
magnetometer team that searched for, and found, lightning on Venus.

Throughout its extended mission, Venus Express will continue collecting
vital data to better understand the evolution of this fascinating planet.

Notes for editors:

This article is making reference to the following papers, appearing in the
29 November 2007 issue of the scientific journal Natu

'A warm layer in Venus' cryosphere and high-altitude measurements of HF,
HCL, H2O and HDO, by J-L.Bertaux et al.

'Venus loses its water through the plasma wake', by S.Barabash et al.

'South-polar features on Venus similar to those near the north pole', by
G.Piccioni et al.

'Lightning on Venus inferred from whistler-mode waves in the ionosphere', by
C.T.Russell et al.

For more information

David Grinspoon, Venus Express Interdisciplinary Scientist
Denver Museum of Nature & Science, Colorado, US
Email: David.Grinspoon @ dmns.org

Chris Russel, MAG co-Investigator
Institute of Geophysics and Planetary Physics, Univ. of California, US
Email: Ctrussel @ igpp.ucla.edu

Fred Taylor, Venus Express interdisciplinary scientist
University of Oxford, UK
Email: Fwt @ atm.ox.ac.uk

Jean-Loup Bertaux, SPICAV/SOIR Principal Investigator
Service d'Aeronomie du CNRS
Email : Jean-Loup.Bertaux @ aerov.jussieu.fr

Giuseppe Piccioni, VIRTIS co-Principal Investigator
IASF-Istituto Nazionale di Astrofisica, Italy
Email: Giuseppe.Piccioni @ iasf-roma.inaf.it

Stanislav Barabash, ASPERA Principal Investigator
Swedish Institute of Space Physics, Kiruna, Sweden
Email: Stas @ irf.se

Hakan Svedhem, ESA's Venus Express Project Scientist
Email: Hakan.Svedhem @ esa.int

[NOTE: Images supporting this release are available at
http://www.esa.int/SPECIALS/Venus_Ex...K373R8F_1.html ]