[meteorite-list] Venus Express: A New Episode of Active Volcanism on Venus?

From: Ron Baalke <baalke_at_meteoritecentral.com>
Date: Mon, 3 Dec 2012 09:59:53 -0800 (PST)
Message-ID: <201212031759.qB3Hxrte023975_at_zagami.jpl.nasa.gov>

http://sci.esa.int/science-e/www/object/index.cfm?fobjectid=51185

A new episode of active volcanism on Venus?
Euoprean Space Agency
02 Dec 2012

For decades, planetary scientists have debated whether Venus possesses
active volcanoes. The latest twist to the tale is provided by data sent
back from ESA's Venus Express orbiter, revealing unexplained major
changes in the amount of sulphur dioxide gas above the planet's dense
cloud layer.

Since Earth and Venus are similar in size and mass, and both planets
formed around the same time and in the same region of the Solar System,
one might expect them to virtual twins. However, Venus is enveloped by a
thick blanket of clouds, composed mainly of sulphuric acid droplets.
Hurricane force winds at the cloud tops sweep around the planet in only
four days - a phenomenon known as super-rotation.

Beneath the clouds, the carbon-dioxide-rich atmosphere has a density 90
times greater than on Earth. This suffocating atmosphere acts like a
greenhouse, trapping solar heat and causing the surface temperature to
soar to around 460 degrees Celsius.

Although it is the closest planet to Earth and it has been visited by
numerous spacecraft, Venus retains many mysteries. One enduring question
is whether there are any active volcanoes.

Radar imagery has revealed more than 1000 volcanic structures and
evidence of possible periodic resurfacing of the planet by floods of
lava. By studying emission of infrared radiation from lava flows around
a volcanic mountain, Venus Express has also found indirect evidence that
volcanism has taken place within the last 2.5 million years. However, no
definitive proof of current volcanic eruptions has yet been found, and
the debate continues to rage.

The latest contribution to the investigation into active Venusian
volcanism comes from the SPICAV-UV spectrometer on board Venus Express,
which has been in orbit around the planet since 2006. By studying the
SPICAV data, a team of scientists from France and Russia has discovered
an unusual change in the amount of sulphur dioxide (SO_2 ) gas in the
upper atmosphere.

The SPICAV data show that the concentration of SO_2 above the main cloud
deck increased slightly to about 1000 parts per billion by volume (ppbv)
between 2006 and 2007, but then steadily decreased over the next five
years, reaching only 100 ppbv by 2012. This is very reminiscent of a
pattern observed by Pioneer Venus during the 1980s, the only other
multi-year dataset of SO_2 measurements.

Since Venus does not experience any seasons, the authors of the paper in
Nature Geoscience suggest two possible explanations: periods of active
volcanism, or long-term variability in the general circulation of the
atmosphere.

"Sulphur dioxide is a key indicator of the processes taking place in
the upper atmosphere of Venus," said Emmanuel Marcq, of LATMOS,
Universit?? de Versailles-Saint-Quentin, France, the lead author of the
paper.

"SO_2 is known to be an important, and constant, constituent of the
lower atmosphere of Venus. A steady supply of SO_2 to high levels is
provided by air rising from the hot, lower atmosphere. When it gets
above the clouds, SO_2 is rapidly destroyed by solar UV light, so it has
a very short life, less than half a day, in the upper atmosphere of Venus."

"This means that the only explanation for a marked rise and fall in
SO_2 concentration at an altitude of 70 km is an enhanced injection of
enriched gas from lower levels, beneath the clouds."

Although SO_2 is an important constituent of volcanic outgassing, the
authors of the paper suggest that the increase observed by Venus Express
may be the result of a plume of heated gases rising to high altitudes,
rather than a direct injection of SO_2 .

"An explosive volcanic eruption, rather like a more powerful version of
the 1991 Mt. Pinatubo eruption on Earth, could act like a piston,
blasting a column of gas up to these levels," said co-author Jean-Loup
Bertaux, Principal Investigator for Venus Express SPICAV instrument that
made the detections. "This extra convection could carry SO_2 above the
clouds and temporarily increase its concentration."

On the other hand, the amount of SO_2 in the lower atmosphere has
remained remarkably stable at very high levels over more than a decade,
and there has been no evidence of an increase in thermal emission from
the planet's surface to coincide with the changes observed by SPICAV.
This opens up the possibility that the increased levels of SO_2 above
the clouds could have been caused by a change in the global atmospheric
circulation which increased the movement of gases from the lower to
upper atmosphere.

"During periods of scarce SO_2 , there is usually a greater amount
above the poles of Venus than near the equator," said Emmanuel Marcq.
"However, this distribution pattern was reversed in our 2006-2007 data
when SO_2 was abundant. This suggests that there may have been stronger
advection (upwelling) near the equator of air from the lower, SO_2
-enriched regions of the atmosphere until 2007. Over the same period of
time, the mean UV brightness of the cloud tops also declined.

"It is possible that long-term variations occur in the atmospheric
circulation, resulting in injections of SO_2 from lower levels and
changes in cloud chemistry, revealed by observations of UV absorption."

"The atmospheric circulation of the planet is not yet fully
understood," said Jean-Loup Bertaux, "but we believe there may be two
simple Hadley cells in which air rises at the equator, spreads out at
cloud level towards the poles, then sinks toward the surface, before
flowing back to the equator.

"Whichever explanation is correct, it seems that the shift in SO_2
concentrations between the poles and equator, as well as the periodic
rise and fall at high altitudes, are consistent with fluctuations in the
SO_2 supply from the lower atmosphere at low latitudes."

"There are very few opportunities to search for evidence of active
volcanism on Venus," said Hakan Svedhem, ESA's project scientist for
Venus Express. "Since there are no other spacecraft studying Venus at
the present time, Venus Express is the only means to find evidence for
such activity. Although it is not yet possible to explain the results,
the SPICAV data are very intriguing and show once again the similarities
in the physical processes that occur on the terrestrial planets."

Notes for editors

The results presented in this article are reported in "Variations of
sulphur dioxide at the cloud top of Venus's dynamic atmosphere" by
Emmanuel Marcq, Jean-Loup Bertaux, Franck Montmessin and Denis Belyaev,
published in the 3 December issue of Nature Geoscience.

Europe's first mission to Venus, Venus Express was launched from
Baikonur Cosmodrome on 9 November 2005 on a Soyuz-Fregat launcher. It
was inserted into Venus orbit on 11 April 2006. Venus Express orbits the
planet in a 24 h period polar orbit. Its payload includes a combination
of spectrometers, spectro-imagers, and imagers covering a wavelength
range from ultraviolet to thermal infrared, a plasma analyser and a
magnetometer.

Venus Express was designed to be the first spacecraft to perform a
global investigation of the Venusian atmosphere and of the plasma
environment. Venus Express reused designs from Mars Express and also
employed spare instruments from Mars Express and Rosetta. The "Express"
in its name denotes the accelerated pace with which it went through the
process from design to launch, taking less than four years.


Contacts

Emmanuel Marcq
Laboratoire Atmosph??res, Milieux, Observations Spatiales (LATMOS)
Universit?? de Versailles-Saint-Quentin, France
E-mail : Emmanuel.Marcq at latmos.ipsl.fr
Phone: +33-1-80-28-52-83

Jean-Loup Bertaux
Laboratoire Atmosph??res, Milieux, Observations Spatiales (LATMOS)
Universit?? de Versailles-Saint-Quentin, France
E-mail: jean-loup.bertaux at latmos.ipsl.fr
Phone: +33-1-80-28-50-62, +33-6-80-73-08-70

Hakan Svedhem
ESA Venus Express Project Scientist
Research and Scientific Support Department
Science and Robotic Exploration Directorate
ESA, The Netherlands
E-mail: H.Svedhem at esa.int
Phone: +31-71-565-3370
Received on Mon 03 Dec 2012 12:59:53 PM PST