Paris, May 16 : Scientists have detected a key molecule in the atmosphere of Venus, a detection that gives them an important new tool to unlock the workings of the planet's dense atmosphere.

Hydroxyl, the molecule that was detected by the Venus Express, is an important but difficult-to-detect molecule.

Made up of a hydrogen and oxygen atom each, hydroxyl has been found in the upper reaches of the Venusian atmosphere, some 100 km above the surface, by Venus Express's Visible and Infrared Thermal Imaging Spectrometer, VIRTIS.

The elusive molecule was detected by turning the spacecraft away from the planet and looking along the faintly visible layer of atmosphere surrounding the planet's disc. The instrument detected the hydroxyl molecules by measuring the amount of infrared light that they give off.

The band of atmosphere in which the glowing hydroxyl molecules are located is very narrow; it is only about 10 km wide.

By looking at the limb of the planet, Venus Express looked along this faint atmospheric layer, increasing the signal strength by about 50.

Hydroxyl is thought to be important for any planet's atmosphere because it is highly reactive.

On Earth, it has a key role in purging pollutants from the atmosphere and is thought to help stabilise the carbon dioxide in the martian atmosphere, preventing it from converting to carbon monoxide.

On Mars, it is also thought to play a vital role in sterilising the soil, making the top layers hostile to microbial life.

The reactive molecule has been seen around comets, but the method of production there is thought to be completely different from the way it forms in planetary atmospheres.

"Because the Venusian atmosphere had not been studied extensively before Venus Express arrived on the scene, we have not been able to confirm much of what our models tell us by observing what is actually happening," said Giuseppe Piccioni, one of the Principal Investigators of the VIRTIS experiment.

"This detection will help us refine our models and learn much more," he added.

On Earth, the glow of hydroxyl in the atmosphere has been shown to be closely linked to the abundance of ozone.

From this study, the same is thought to be true at Venus. Now, scientists can set about estimating the amount of ozone in the planet's atmosphere.

Venus Express has shown that the amount of hydroxyl at Venus is highly variable. It can change by 50% from one orbit to the next and this may be caused by differing amounts of ozone in the atmosphere.

"Venus Express has already shown us that Venus is much more Earth-like than once thought. The detection of hydroxyl brings it a step closer," said Piccioni.