Europe's first mission to Venus is set for launch later this month. Credit: ESA

Get set for a revival of interest in Earth's wayward twin. The European Space Agency (ESA) plans to launch Venus Express next week — the first visit to the planet in more than a decade. The focus of the €220-million (US$265-million) mission will be the planet's thick atmosphere, which some think could host exotic life forms that use ultraviolet instead of visible light.

Venus Express will begin its journey from Kazakhstan on a Soyuz–Fregat rocket; the month-long launch window opens on 26 October. ESA developed the mission — its first to Venus — in less than four years, after asking the science community for ideas on adapting its Mars Express spacecraft for another purpose.

The craft uses cameras and spectrometers adapted from Mars Express and Rosetta, an upcoming comet mission. These will build up a three-dimensional profile of Venus's carbon dioxide-rich atmosphere, which traps heat and drives temperatures on the surface to a searing 450 °C. Past missions, including the 1978 Pioneer Venus orbiter and the Magellan surface-mapper of the 1990s, have hinted at active volcanism and lightning on the planet; Venus Express will investigate these observations further.

The mission may also help to determine what is absorbing ultraviolet radiation in the planet's clouds. David Grinspoon of the Southwest Research Institute in Boulder, Colorado, and others speculate that life may have evolved that thrives in acidic environments and photosynthesizes ultraviolet light. Rather than living on the hot surface, such organisms might reside in long-lived clouds, where temperatures and pressures are more Earth-like.

Grinspoon has been modelling the history of Venus's atmosphere, and his preliminary results indicate that the planet's early ocean could have persisted for as long as 2 billion years. Life could have adapted to the clouds when the surface water disappeared, he suggests.

Grinspoon calls this a kind of “thought experiment”, and does not claim there is evidence for life on Venus today. Nor does he believe that terrestrial microbes stowing away on Venus Express risk contaminating the planet. Current international guidelines for planetary protection require sterilization for Mars-bound spacecraft, but not for those headed for hot and acidic Venus.

Still, NASA has asked the US National Academy of Sciences, based in Washington DC, to revisit the subject of planetary protection for Venus. Thirty years have passed since it last looked at the question, says NASA planetary-protection officer John Rummel. At present, the agency is mulling over ideas for sample-return missions to Venus, and the academy has recommended that a lander be sent to the planet in the next decade.

In the meantime, Japan plans to launch its Venus Climate Orbiter in 2008, and two Mercury-bound spacecraft — MESSENGER and BepiColombo — will study Venus during brief fly-bys.