Mysteries of Venus revealed at wavelengths invisible to human eyes

December 04, 2008

New images taken by instruments on board ESA's Venus Express provide a unique insight into the windy atmosphere of our neighbouring planet and reveal that global patterns at the Venus cloud tops are the result of variable temperatures and cloud heights.

Using the spacecraft's ultraviolet and infrared cameras, the Venus Express team, including UK scientists, have been able to compare what the planet looks like at different wavelengths, allowing them to study the physical conditions and dynamics of the planet's atmosphere. These results appear today (4th December) in the journal Nature.

Professor Fred Taylor, one of the Venus Express scientists, from Oxford University and funded by the UK's Science and Technology Facilities Council, said, "The features seen on Venus in ultraviolet light have been a puzzle to astronomers for nearly a century. These new images have revealed the structure in the clouds that produces them and shows how they result from complex meteorological behaviour. We can now study in much greater detail and try to understand the origin of features such as the large hurricane-like vortex over the north and south poles. Like many things on Venus, including global warming, this feature has similarities to atmospheric and environmental process on Earth, but the Venus version is much more extreme."

Observations made with the ultraviolet camera show numerous high-contrast features. The cause is the uneven distribution of a mysterious chemical in the atmosphere that absorbs ultraviolet light, creating bright and dark zones. But the exact chemical species that creates the high-contrast zones still remains elusive. Most simple candidates have been ruled out, and a complex compound of sulphur is now the favourite. It will probably take measurements inside the clouds to identify it, but we do know that Venus' atmosphere is loaded with sulphur from volcanic eruptions on the surface below.

The ultraviolet images also reveal the structure of the clouds and the dynamical conditions in the atmosphere, whereas the infrared data provides information on the temperature and altitude of the cloud tops.

Professor Keith Mason, Chief Executive of the Science and Technology Facilities Council, said "These new images provide us with a wealth of information about the atmospheric conditions of this fascinating neighbour planet. We can now study Venus in greater detail to understand more about its complex processes. "

With data from Venus Express, scientists have learnt that the equatorial areas on Venus that appear dark in ultraviolet light are regions of relatively high temperature, where intense convection brings up the mysterious dark material from below. In contrast, the bright regions at mid-latitudes are areas where the temperature in the atmosphere decreases with depth, which prevents air from rising. The effect is most extreme in a wide belt around each pole, nicknamed the 'cold collar', which appears darkest, hence coldest, in infrared measurements, but as a bright band in the ultraviolet images.

Observations in the infrared have been used to map the altitude of the cloud tops. Surprisingly, the clouds in both the dark tropics and the bright mid-latitudes are located at about the same height of about 72 km above the surface. At 60 degrees of latitude, the cloud tops start to sink, reaching a minimum of about 64 km at the 'eye' of a huge hurricane-like vortex at the pole, which measures about 2000 km across and rotates around the pole in about 2.5 days.
-end-
Notes for editors

Images

1. Venus in the ultraviolet
http://www.stfc.ac.uk/resources/image/venus1.jpg

Venus Monitoring Camera image taken in the ultraviolet (0.365 micrometres), from a distance of about 30000 km.

It shows numerous high-contrast features, caused by an unknown chemical in the clouds that absorbs ultraviolet light, creating the bright and dark zones.

With data from Venus Express, scientists have learnt that the equatorial areas on Venus that appear dark in ultraviolet light are regions of relatively high temperature, where intense convection brings up dark material from below. In contrast, the bright regions at mid-latitudes are areas where the temperature in the atmosphere decreases with depth. The temperature reaches a minimum at the cloud tops suppressing vertical mixing. This annulus of cold air, nicknamed the 'cold collar', appears as a bright band in the ultraviolet images.

Credits: ESA/MPS/DLR/IDA.

2. Venus in the ultraviolet and the infrared
http://www.stfc.ac.uk/resources/image/venus2.jpg

Using Venus Express, it is possible to compare what the planet looks like at different wavelengths, giving scientists a powerful tool with which to study this planet's turbulent atmosphere.

The lower left shows a map of temperature inversion at the venusian cloud tops, derived from the Visible and Infrared Thermal Imaging Spectrometer, VIRTIS, on the planet's night-side. The darker the region, the colder the cloud tops. To the upper right is an ultraviolet image of the venusian day side, captured by the Venus Monitoring Camera, VMC, simultaneously with the night-side infrared image.

The ultraviolet reveals the structure of the clouds and the dynamical conditions in the atmosphere, whereas the infrared provides information on the temperature and altitude of the cloud tops.

Credits: VMC: ESA/MPS/DLR/IDA VIRTIS: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA.

3. Altimetry of the cloud tops
http://www.stfc.ac.uk/resources/image/venus3.jpg

A Venus Monitoring Camera ultraviolet image with a superimposed colour mosaic, showing the altitude of the cloud tops. The colour mosaic was derived from simultaneous pressure measurements by the Visible and Infrared Thermal Imaging Spectrometer.

Credits: VMC: ESA/MPS/DLR/IDA VIRTIS: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA.

4. Venus's southern hemisphere
http://www.stfc.ac.uk/resources/image/venus4a.jpg
http://www.stfc.ac.uk/resources/image/venus4b.jpg
http://www.stfc.ac.uk/resources/image/venus4c.jpg

In this mosaic, infrared images taken at a wavelength of 5 micrometres (in red) are overlaid on ultraviolet images, taken at 0.365 micrometres.

The bright areas in the infrared images track the temperatures at the cloud tops. The oval feature that stands out in these images is the giant eye of a hurricane, or the polar vortex, at the planet's south pole. Its centre is displaced from the south pole and the structure measures about 2000 km across, rotating around the pole in about 2.5 days. The atmosphere rotates anticlockwise in the figure.

Credits: VMC: ESA/MPS/DLR/IDA VIRTIS: ESA/VIRTIS/INAF-IASF/Obs. de Paris-LESIA.

Contacts

Julia Short
STFC Press Office
Tel: +44 (0)1793 442 012
Mob: +44 (0)777 027 6721
Email: julia.short@stfc.ac.uk

Professor Fredric Taylor
University of Oxford
Email: fwt@atm.ox.ac.uk

Links

Venus express mission on the ESA website
http://sci.esa.int/science-e/www/area/index.cfm?fareaid=64

UK scientists play key roles in Venus Express with teams from University of Oxford, UCL's Mullard Space Science Laboratory, University of Sheffield, Imperial College London, the Science and Technology Facility Council's Rutherford Appleton Laboratory and University of Aberystwyth contributing to the hardware and science operations. UK industry have fundamental roles in the mission with EADS Astrium the prime contractor for the spacecraft and SciSys Ltd providing mission control software commanding of Venus Express and the monitoring of its onboard state.

Science and Technology Facilities Council

The Science and Technology Facilities Council ensures the UK retains its leading place on the world stage by delivering world-class science; accessing and hosting international facilities; developing innovative technologies; and increasing the socio-economic impact of its research through effective knowledge exchange partnerships.

The Council has a broad science portfolio including Astronomy, Particle Physics, Particle Astrophysics, Nuclear Physics, Space Science, Synchrotron Radiation, Neutron Sources and High Power Lasers. In addition the Council manages and operates three internationally renowned laboratories: The Council gives researchers access to world-class facilities and funds the UK membership of international bodies such as the European Laboratory for Particle Physics (CERN), the Institute Laue Langevin (ILL), European Synchrotron Radiation Facility (ESRF), the European organisation for Astronomical Research in the Southern Hemisphere (ESO) and the European Space Agency (ESA). It also contributes money for the UK telescopes overseas on La Palma, Hawaii, Australia and in Chile, and the MERLIN/VLBI National Facility, which includes the Lovell Telescope at Jodrell Bank Observatory.

The Council distributes public money from the Government to support scientific research. Between 2008 and 2009 we will invest approximately £787 million.

The Council is a partner in the UK space programme, coordinated by the British National Space Centre.

Science and Technology Facilities Council

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