First detection of interstellar O₂

Astrochemists have long argued that the Life molecules water (H₂O) and oxygen (O₂) are highly abundant in the dense interstellar medium. The level of abundance was assumed so high that these molecules would actually dominate the energy balance of molecular clouds. Whether this is indeed the case is an important issue also for astrophysicists, as it would control the time evolution of the clouds, eventually leading to new generations of stars and planetary systems.

An international consortium of scientists from Sweden, Canada, France and Finland decided that this was so important that they would test the theory. Unfortunately, it is not an easy task, as the molecules one likes to observe from distant objects are also present in large numbers in our own atmosphere. Telescopes therefore need be placed in space. The Odin satellite is such an observatory in orbit around the Earth, especially built for the detection of H₂O and O₂.

Since its launch five years ago, Odin has observed prominent interstellar clouds in the search for these molecules. Given the very optimistic theoretical predictions, it came as a bad surprise that there was not a trace of oxygen. Also the amount of water found in the clouds was much less than had been anticipated. Theorists have since tried to explain these odd, unexpected findings.

It therefore comes as a great relief that the IR-group at Stockholm Observatory announces that using Odin they have finally seen the long searched for O₂. This discovery is immensely important as it will lead to new, invaluable insight into the complex development of interstellar clouds forming stars and planets.