ESA title
Science & Exploration

ISO factsheet

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ESA / Science & Exploration / Space Science

Probing the cool and hidden Universe

Name ISO stands for the Infrared Space Observatory.

Description In its time, the Infrared Space Observatory (ISO) was the most sensitive infrared satellite ever launched. ISO made particularly important studies of the dusty regions of the Universe, where visible light telescopes can see nothing. The wealth of data collected by ISO still produces important science results.

Launch 17 November 1995 (Ariane 44P launcher at Kourou, French Guiana).

Status Completed (1998).

Journey ISO's highly elliptical orbit around the Earth took almost 24 hours. For almost 17 hours per day, ISO was outside the radiation belts surrounding Earth. Scientists could operate all ISO's detectors during this time.

Notes On average, ISO performed 45 observations per revolution (a period of almost 24 hours) - an observation every 32 minutes.

Infrared radiation is primarily 'heat', or thermal radiation. Even 'cold' ice cubes, emit infrared radiation. For this reason, ISO, which operates at wavelengths from 2.5 to 240 microns, could observe objects that remain hidden for optical telescopes, such as cool objects that are unable to emit in visible light.

ISO has observed many galaxies which are half as old as the Universe by staring through a window in the dust of our own Milky Way Galaxy, called the Lockman Hole.

Observing the cool Universe requires cool instruments that can work at temperatures close to absolute zero, -273°C. ISO used a coolant to maintain a low temperature.

In April 1998, ISO ran out of the coolant needed to keep its detectors working. ISO was switched off in May 1998. Prior to this, scientists changed its orbit to make the satellite eventually burn up in the Earth's atmosphere (possibly in 2014).

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