A European satellite has detected a reservoir of ice in the dusty outer reaches of a planetary system forming around a nearby ten-million-year-old star.

Michiel Hogerheijde of the Leiden Observatory in the Netherlands and his colleagues analysed data from the Herschel Space Observatory. From these, they identified a thin layer of water vapour that implies the existence of water ice — several thousand Earth oceans' worth — locked in the ice-coated grains of the circumstellar dust disk.

The measured spin characteristics of the hydrogen atoms in the water vapour, which may indicate the location of ice formation, differ from those of watery comets in our Solar System. This suggests that substantial mixing of ice occurs across a planetary disk, which comets then collect during the early stages of planet formation. Comets are thought to be responsible for delivering water to inner-Solar-System planets such as Earth.

Science 334, 338–340 (2011)