The restless atmosphere of Venus (Forwarded)

ESA News
http://www.esa.int

28 November 2007

The restless atmosphere of Venus

Venus Express has studied the true extent of Venus' restless atmosphere.
This includes the planet's glow, its highly variable south polar vortex and
the dynamic upper atmosphere, different from what is seen on any other rocky
planet of the Solar System.

Venus' faint glow of light coming from molecules in the atmosphere is
providing scientists a detailed look into its physical and chemical
processes.

The first triumph for Venus Express was to uncover the planet's dramatic
south polar vortex in unprecedented, fine detail. The vortex powerfully
drives the cloud dynamics at all altitudes. "It plays an important role in
balancing the atmosphere," says Giuseppe Piccioni, VIRTIS co-Principal
Investigator at IASF-Istituto Nazionale di Astrofisica, Italy, who used the
Visible and Infrared Thermal Imaging Spectrometer (VIRTIS) instrument on
Venus Express to discover and study the structure.

Planetary scientists believe that the double hurricane-like feature is
formed when warm air from the equatorial regions of Venus rises into the
atmosphere and travels down towards the pole of the planet. Once there, it
begins to cool and sink, spiralling down to create the vortex.

Venus Express has also revealed new details about the turbulent region known
as the 'sub-solar' region. This is the part of the planet that faces the
Sun, which changes slowly as Venus rotates. It is the area of Venus that
absorbs most of the incoming heat from the Sun, making it a crucial location
for the atmospheric dynamics.

As the heat streams into the atmosphere, the gas breaks up into rolling
pockets known as convection cells. "It is as if the whole region is
boiling," says Wojtech Markiewicz, VMC Principal Investigator at the
Max-Planck-Institute for Solar System Research, Germany, drawing an analogy
to the way milk boils in a pan.

Previous observations had hinted that the convection cells might be as large
as 200 km across, but this was difficult to explain using conventional
atmospheric physics. Venus Express observations clearly show that the cells
are much smaller, about 2030 km. At this size, the cells are probably
confined to the mid-atmosphere, leaving a stable atmospheric layer below.

Venus has a high-altitude haze layer composed of brightly reflecting aerosol
particles and a new mystery has been revealed. On 13 January 2007, under the
gaze of Venus Express's instruments, two thirds of the planet's southern
hemisphere suddenly brightened as something triggered the aerosols to form
at a furious rate. As yet, no one knows what started this amazing
transformation. The feature disappeared just as quickly a few days later
when the aerosols had coagulated and the haze had cleared up.

Venus Express has also seen the glow from molecules of oxygen and carbon
dioxide in the atmosphere of the planet. In the case of carbon dioxide, the
'airglow' is produced when the molecule absorbs and then re-emits a photon
from the Sun. This happens quite quickly and the glow from carbon dioxide is
confined to the day-side and low-pressure altitudes of the planet.

In contrast, the faint glow from oxygen has been detected from night side of
the planet. This indicates a different mechanism at play. Indeed, the oxygen
glows when two stray oxygen atoms join together, releasing some energy. Both
types of emission tell scientists about the conditions in the atmosphere.

"The airglow allows us to constrain models of the atmosphere," says Pierre
Drossart, Observatoire de Paris, France, and the VIRTIS co-Principal
Investigator. Already, the Venus Express results have allowed planetary
scientists to adjust the temperatures in the atmosphere in their computer
models to more realistic values.

Most importantly, Venus Express is monitoring changes in the airglow that
occur across the planet and at different times. This is providing planetary
scientists with an unprecedented level of detail and, as Drossart says,
"Science is made of the details."

Venus Express is certainly providing them.

Notes for editors:

The findings will appear in 29 November issue of the scientific journal
Nature, in the following papers:

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

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

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

Findings related to the study of the upper atmosphere will appear in the
article:

'The distribution of the 02 infrared nightglow observed with VIRTIS on board
Venus Exppress', by J-C. Gerard et al., accepted for publication in the
Geophysical Research Letters.

For more information:

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

Pierre Drossart, VIRTIS co-Principal Investigator
Observatoire de Paris, France
Email : pierre.drossart @ obspm.fr

Wojtech Markiewicz, VMC Principal Investigator
Max-Planck-Institute for Solar System Research, Germany
Email: markiewicz @ mps.mpg.de

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...F373R8F_1.html ]