Mullard Space Science Laboratory

P R E S S  R E L E A S E

25 May 2004
REF: VT2004-1


The transit of Venus across the face of the Sun on 8 June is relevant for three aspects of work at UCL's Mullard Space Science Laboratory. First, MSSL are working on an experiment for the European Space Agency's Venus Express mission flying to Venus next year. Second, they are using this transit to demonstrate a method of discovering Earth-sized planets around other stars, for use on future space missions. Third, they study the Sun from spacecraft continuously - and some of these spacecraft will see the transit on the day.

The laboratory will host an event for invited local schools on the morning of 8 June, where it will be possible to view the spectacle live and in safety, and relevant work will be highlighted.

The rare transit offers a remarkable link between the past, present and future. In the past, one of the transits (in 1761) provided the first hint that Venus may have an atmosphere. In the present, we now know that Venus has an atmosphere of 90 times the pressure of Earth's atmosphere - equivalent to the pressure hundreds of metres under Earth's ocean surface. In the future, spacecraft will explore Venus to study some of the remaining puzzles about the planet, and others will use the transit technique for planet hunting around other Sun-like stars.

Europe's Venus Express mission, for launch in November 2005, will reach our sister planet 5 months later. It will be making important new measurements on the atmosphere, the surface and the escape of atmosphere to space. This will tell us more about Earth's hellish twin - where the clouds are made of sulphuric acid, the surface temperature is 460 degrees Celsius and a runaway greenhouse effect has been active for billions of years.

Venus Express will use newly-discovered 'windows' in infrared light to probe the atmosphere under the clouds, and the surface. This will help to explain why the thick Venus atmosphere rotates so quickly above the slowly rotating surface, producing the chevron-shaped clouds seen in pictures from earlier spacecraft. Used with another new instrument, a ground-penetrating radar, the anticipated, but never detected, volcanism should be seen if it is still active on the surface.

The Venus Express instrument MSSL are working on is ASPERA, which will measure in detail, for the first time, how the outer parts of the Venus atmosphere are stripped away by the solar wind and lost to space. Similar to Mars, Venus has no magnetic field to protect its atmosphere from this effect. In contrast, our Earth has a magnetic shield which protects us from the solar wind and from cosmic rays.

Dr Andrew Coates, co-investigator on Venus (and Mars) Express, says 'In Venus case, it is thought that the stripping of the atmosphere may be constantly replenished by volcanism; in Mars case, the atmosphere has been mostly scavenged away to space or frozen under the surface. By comparing planetary environments in this way, we will discover more about our own.'

MSSL scientists will be simulating an extrasolar planet transit - using technology developed for use in space-based extrasolar planet hunting. A detector, designed for use on ESA's Eddington mission, will be used on 8 June.

Dr Dave Walton, who will perform the experiment, says 'This will be a unique experiment using this special detector to measure the very small decrease in brightness, dipping by less than a tenth of one percent, during the transit. This will be an interesting test of the technique for future space missions.'

The event will also be seen by the SOHO and TRACE spacecraft, used to study the Sun. Images should be available on the day.


Notes to Editors:

1. The Mullard Space Science Laboratory, situated at Holmbury St Mary, is the Department of Space and Climate Physics of University College London. About 120 people work on space science and space engineering. The Laboratory plays key roles in many missions of space exploration. Over 250 instruments have been launched into space to date, to study astrophysics, solar and stellar physics, plasma and planetary physics and climate physics.

2. Venus Express is a mission of the European Space Agency's Science Programme

C O N T A C T S:

Mullard Space Science Laboratory
University College London
Holmbury St. Mary, Dorking
Surrey, RH5 6NT

MSSL switchboard: 01483 204100
MSSL website:

Schools event: Tracey Poole
Venus Express: Andrew Coates and Dhiren Kataria
Eddington experiment: Dave Walton