|ISO was the world's first space observatory able to see the sky in infrared light. This pioneering position allowed ISO to unveil a new 'face' of the Universe, its infrared face. This has changed radically our view of the Universe. ISO operated between November 1995 and May 1998, and made 30 000 scientific observations.
Infrared light is invisible to the human eye and to optical telescopes, which are sensitive to the same light the human eye can see. Moreover, the Earth's atmosphere prevents most infrared radiation from reaching the ground, so a space telescope is needed to detect it. For these reasons, the infrared universe was very poorly known until ISO. All objects emit infrared radiation. The sky therefore looks very different when seen in the infrared. ISO could see objects and processes that are too cold or too dusty, or both, to appear when you look through optical telescopes, such as clouds in which stars are being born.
ISO's results impact most fields of astronomical research, from comets to cosmology. One of ISO's greatest achievements was the discovery that the water molecule is very common in many regions on the Universe, even in distant galaxies. Astronomers from all over the world continue to make frequent discoveries by studing the observations stored in the ISO data archive.