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The composite picture shows fingerprints of water vapour (labelled H2O) in widely differing infrared wavebands, as registered by two instruments of ESA's space telescope ISO when it was trained on the elderly star W Hydrae. In a high-resolution spectrum from the Short Wavelength Spectrometer (SWS) the main water feature is the strong emission at wavelengths around 38 microns. The Long Wavelength Spectrometer (LWS) picked up a large number of strong water-vapour emissions at wavelengths from 122 to 183 microns.

The two spectra are overlaid on an image taken with the camera ISOCAM at wavelengths of 7 and 15 microns. It shows the dark star-forming cloud called Rho Ophiuchi, partially opened to view by the penetrating power of ISO's infrared "eyes".

ISO's spectrometers have detected water in the vicinity of newly forming stars as well as near dying stars. Indeed ISO is finding water throughout the Galaxy -- in our own backyard in comets like Hale-Bopp and on the outer planets, and in far-flung clouds towards the centre of the Milky Way.