Astronomers decided to search for the fingerprint in the light coming from two regions in the galactic centre. These regions were selected because light emitted from there passes through several cold clouds on its way to Earth. Cold water is also very abundant Moneti and his colleagues used data stored in the ISO Archive, and were lucky. They detected the presence of both water vapour and solid ices in the cold regions. Now for the first time they can estimate the global amount of water available in these places and its relative abundance as compared with other molecules.
Water turns out to be very abundant.
Its average temperature is that of the cloud, -263 degrees C. Astronomers estimate that there are millions of cold clouds in the Milky Way. The fact that cold and warm clouds have the same amount of water is surprising, because some hypotheses suggested that the molecule was best preserved by processes happening exclusively in warm clouds. This ISO finding therefore gives new insights into the question of how water is formed and preserved in space. Although the process is not yet fully understood, a simplified description is that part of the ice remains unprocessed and ends up in comets, while the rest turns into vapour and is used, together with the original water vapour, to make planetary atmospheres and gaseous planets. It is not yet clear how the water contained in the gas and in the grains contributes to form planetary atmospheres, but it is clear that a lot of processing occurs in the planets.