The enormous success of IRAS stimulated both the European Space Agency (ESA) and NASA to develop new space infrared observatories that would follow up the wealth of discoveries about the infrared universe made with IRAS.

Early in February 1983, the European Space Agency met to select a new medium-sized astronomy space mission. Peter Clegg was able to place on the table at the meeting the first scan around the sky from IRAS, and its quality was sufficient to convince the European Space Agency to select the Infrared Space Observatory (ISO). The idea for a European infrared space observatory had been first proposed in 1979. ISO was finally launched in November 1995 with a planned life of 18 months (Figure 10.1). In fact, its helium coolant lasted until April 1998, almost a year longer than expected.

ISO had a camera, ISOCAM, led by Catherine Cesarsky and a spectrometer, SWS, led by Thijs de Graauw, working at the near- and mid-infrared wavelengths (3–20 microns); and a camera, ISOPHOT, led by Dietrich Lemke and a spectrometer, LWS, led by Peter Clegg, working at far-infrared (40–160 micron) wavelengths. The two cameras also had smaller low-resolution spectrometers as part of their capability. The spectrometers of ISO were especially powerful in unravelling the nature of the dust around stars and in interstellar space, and in probing young stars in the process of formation.