Spitzer Space Telescope

The Spitzer Space Telescope launched on August 25, 2003, completing NASA’s quartet of Great Observatories. Cooled to just a few degrees above absolute zero and placed in an Earth-trailing orbit around the Sun, Spitzer saw the universe in infrared — the light of cool stars, warm dust, and galaxies whose visible light had been stretched by billions of years of cosmic expansion.

Spitzer traced the structure of stellar nurseries, discovered Saturn’s enormous outer ring, and became an unexpected exoplanet powerhouse: its measurements helped reveal that the TRAPPIST-1 system holds seven Earth-sized planets. It observed for more than 16 years, far outliving its cryogen, before being retired in January 2020.