NASA's Spitzer Space Telescope which was initially scheduled for 2.5-year primary mission has completed 15 years of space exploration.
Launched into a solar orbit in 2003, Spitzer has illuminated some of the oldest galaxies in the universe, revealed a new ring around Saturn, and peered through shrouds of dust to study newborn stars and black holes.
It assisted in the discovery of planets beyond our solar system, including the detection of seven Earth-size planets orbiting the star TRAPPIST-1, among other accomplishments.
"In its 15 years of operations, Spitzer has opened our eyes to new ways of viewing the universe," said Paul Hertz, director of the Astrophysics Division at NASA Headquarters in the US.
"Spitzer's discoveries extend from our own planetary backyard, to planets around other stars, to the far reaches of the universe. And by working in collaboration with NASA's other Great Observatories, Spitzer has helped scientists gain a more complete picture of many cosmic phenomena," he said.
With its infrared vision and high sensitivity, Spitzer has contributed to the study of some of the most distant galaxies in the known universe.
The light from some of those galaxies travelled for 13.4 billion years to reach Earth. As a result, scientists see these galaxies as they were less than 400 million years after the birth of the universe.
In recent years, scientists have utilised Spitzer to study exoplanets, or planets orbiting stars other than our Sun, although this was not something the telescope's designers anticipated.
Spitzer also 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.
The TRAPPIST-1 planetary system was unlike any alien solar system ever discovered, with three of its seven planets located in the "habitable zone," where the temperature might be right for liquid water to exist on the planets' surfaces.
Their discovery was an enticing step in the search for life elsewhere in the universe.
"The study of extrasolar planets was still in its infancy when Spitzer launched, but in recent years, often more than half of Spitzer's observation time is used for studies of exoplanets or searches for exoplanets," said Lisa Storrie-Lombardi, Spitzer's project manager at JPL.
"Spitzer is very good at characterising exoplanets, even though it wasn't designed to do that," said Storrie-Lombardi.
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.
In July 2009, after Spitzer's helium supply ran out, the spacecraft entered a so-called "warm phase."
Spitzer's main instrument, called the Infrared Array Camera (IRAC), has four cameras, two of which continue to operate in the warm phase with the same sensitivity they maintained during the cold phase.