The Spitzer Space Telescope, formerly known as the Space Infrared Telescope Facility, is an infrared telescope that studies the early universe, young galaxies and forming stars, and is used to detect dust disks around stars. It is considered an important signpost of planetary formation.
The mission is the fourth and final observatory under NASA's Great Observatories program, which also includes the Hubble Space Telescope, Chandra X-Ray Observatory and Compton Gamma Ray Observatory.
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Spitzer was launched into solar orbit on August 25, 2003, it was initially scheduled for a minimum 2.5-year primary mission. But the space telescope has lasted far beyond its expected lifetime.
In recent years, often more than half of Spitzer's observation time is used for studies of exoplanets or searches for exoplanets. It played a key role in one of the most significant exoplanet discoveries in history: the detection of seven, roughly Earth-size planets orbiting a single star.
Spitzer has logged over 106,000 hours of observation time. Thousands of scientists around the world have utilised Spitzer data in their studies, and Spitzer data is cited in more than 8,000 published papers.
Spitzer's primary mission ended up lasting 5.5 years, during which time the spacecraft operated in a cold phase, with a supply of liquid helium cooling three onboard instruments to just above absolute zero.
The cooling system reduced excess heat from the instruments themselves that could contaminate their observations. This gave Spitzer very high sensitivity for "cold" objects.
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In July 2009, after Spitzer's helium supply ran out, the spacecraft entered a so-called warm phase.
Spitzer's main instrument is the Infrared Array Camera (IRAC). It consists of four cameras, two of which continue to operate in the warm phase with the same sensitivity they maintained during the cold phase.