'Bittersweet day.' NASA says farewell to its Spitzer Space Telescope

After staring past the dusty veils of the cosmos for 16 years, NASA's Spitzer Space Telescope will shut its proverbial eyes Thursday after mission officials at Jet Propulsion Laboratory send the observatory its final command.

The spacecraft probed some of the earliest-known galaxies in the universe and identified rocky, Earth-sized planets orbiting a nearby star. It has also uncovered hundreds of stellar nurseries, cool stars and objects shrouded by interstellar dust.

Spitzer was one of NASA's four Great Observatories, each tasked with sketching out a view of the universe in a different band of the electromagnetic spectrum. Together, they painted a richer portrait of the cosmos.

For instance, while the Hubble Space Telescope was built to scan the skies primarily for visible and ultraviolet light, Spitzer peered into much