Venus: Earth's twin planet? (Forwarded)

ESA News
http://www.esa.int

28 November 2007

Venus: Earth's twin planet?

ESA's Venus Express has revealed Venus as never before. For the first time,
scientists are able to investigate from the top of its atmosphere, down
nearly to the surface. They have shown it to be a planet of surprises that
may once have been more Earth-like, and still is, to a certain extent.

The latest results from the mission were presented today at a press
conference held at ESA headquarters in Paris, and will appear in the 29
November issue of the scientific journal Nature.

Permanently covered in clouds, Venus has been a mystery for centuries.
Although it is the planet nearest to Earth, it has proved extraordinarily
difficult to study because of its curtain of clouds that obscures our view
of its surface.

"It is really surprising how un-Earth-like Venus is now," says Fred Taylor,
a Venus Express interdisciplinary scientist, University of Oxford, UK. Venus
has approximately the same mass as the Earth yet it is a hellish place where
surface temperatures are over 400 C and the surface pressure is a hundred
times that on Earth.

The key to understanding Venus lies in its atmosphere. It is much thicker
than Earth's and intercepts most of the Sun's energy before it can reach the
surface. That's where Venus Express comes in.

"Today's results focus on the different science themes Venus Express is
covering," says Dmitri Titov, Venus Express science coordinator from the
Max-Planck-Institute for Solar System Research, Germany. "An important first
set of results concerns the complex dynamics and structure of Venus's
atmosphere, studied with a whole suite of instruments."

Titov added, "The spacecraft has revealed the structure and movements of the
atmosphere, from its upper reaches to just above the surface, and has
obtained the best global map of atmospheric temperatures to date. This is
already improving our understanding of the global dynamics and the
meteorology of Venus."

"It is worthwhile mentioning the amazing 3D images of the south polar
vortex, the fine details of clouds some very Earth-like and hazes, precise
wind measurements, and the nicest views ever of the phenomena that make
Venus glow in space at infrared wavelengths," added Hakan Svedhem, ESA's
project scientist for Venus Express.

A second set of results concerns both the atmosphere's composition and its
chemistry. Venus Express has taken compositional profiles of the atmosphere
around the planet, and unambiguously confirmed the presence of lightning
which can have a strong effect on the composition of the atmosphere itself.

The challenge for scientists now is to match those readings of the
atmosphere's composition with known gases, because they behave differently
in the extraordinarily high-pressure environment on Venus than they do on
Earth or Mars. "We are only at the beginning of this work," says Titov, "but
we know new surprises are waiting for us."

A third set of results is about the processes by which the atmosphere of
Venus is escaping into space. This is driven by the solar wind -- a stream
of electrically charged particles given out by the Sun. As the solar
particles collide with electrically charged particles near Venus, they
energise the gases, stripping them forever from the planet.

Venus Express has provided giant leaps in the understanding of all these
phenomena, and found how Venus loses water due its interaction with the
solar wind. New measurements of heavy water in the atmosphere are also
providing new clues on the history of water on the planet and its overall
climate evolution.

However, not all mysteries are solved yet. One key answer that scientists
would still like to know is just how active the volcanoes of Venus are. "The
contribution of volcanoes to the atmosphere could be enormous. Not knowing
leaves a huge hole in our understanding of the climate," says Taylor.

For a planet that was once thought to resemble Earth, to one that was
thought to be completely dissimilar, the tables have turned again. Thanks to
Venus Express, Taylor now describes Venus as "Earth's twin, but separated at
birth."

Notes for editors:

Venus Express has now completed its nominal mission. This involved watching
the planet for two venusian days, which, because Venus rotates so slowly,
lasted approximately 500 Earth days.

Venus Express will now start its extended mission to watch the planet for
two more venusian days. One of the things that it will be doing is to look
for the telltale infrared radiation from lava flows, but the analysis is
proving difficult. In 2010, a Japanese mission, Venus Climate Orbiter also
called Planet-C, will arrive at Venus and this will allow scientists to
compare results from the two spacecraft.

More than 250 scientists and engineers across Europe are involved in the
Venus Express mission, supported by their institutes and national space
agencies. The mission also sees the contribution of scientists from Russia
and Japan, as well as from NASA, which sponsors 15 American Venus Express
scientists and provides support to the radio science investigation via its
Deep Space Network antennas.

The contents of this article are reflected in 'Venus as a more Earth-like
planet', to be published in tomorrow's issue of Nature. The paper is by H.
Svedhem, D. Titov, F. Taylor and O. Witasse.

The latest Venus Express results that will all appear in the 29 November
2007 issue of Nature are as follows:

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

'The structure of Venus' middle atmosphere and Ionosphere' by M. Patzold, B.
Hausler et al.

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

'Morphology and dynamics of the upper cloud layer of Venus' by W.
Markiewicz, D. Titov et al.

'A dynamic upper atmosphere of Venus as revealed by VIRTIS on Venus Express'
P. Drossart, G. Piccioni et al.

'Venus loses its water through the plasma wake' by S. Barabash, A. Fedorov
et al. 'Little or no solar wind enters Venus' atmosphere at solar minimum'
by T. Zhang, M. Delva, et al.

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


For more information:

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

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

Dmitri Titov, Venus Express science coordinator, Max-Planck-Institute for
Solar System Research, Germany
Email: Titov @ mps.mpg.de

[NOTE: Images supporting this release are available at
http://www.esa.int/SPECIALS/Venus_Ex...N373R8F_1.html ]