In hot pursuit of cold stars

The mysterious, middle stages of star formation, which are shrouded from the astronomer because they happen inside a huge dust cloud, will be revealed by the European Space Agency's Infrared Space Observatory, which is due for launch next week.

ISO will explore the invisible, cold parts of the universe by detecting infrared radiation - heat. Such a mission has only been done once before, by a satellite which catalogued the infrared sky 12 years ago.

Instead of just scanning the heavens, ISO will seek out specific objects for study. These include areas of star formation, primitive galaxies and Saturn's hazy moon, Titan, which may have an atmosphere similar to the earth's billions of years ago.

David Southwood, head of ESA's science programme committee, said: "My feeling is that it is going to find all sorts of things that stimulate ideas on how things form because it's looking at cold material. It will be understanding where things come from."

The big challenge of the project has been to avoid picking up the infrared that radiates from objects such as the earth, the sun and even the telescope itself. The telescope will be kept in a giant thermos flask, at three degrees above absolute zero.

Its interior has been made dark, a feat that was "much more difficult to achieve than is apparant at first sight," said Peter Clegg, principal investigator for one of the four instruments attached to the telescope and professor of astrophysics at Queen Mary and Westfield College.