As NASA’s Spitzer telescope’s mission ends, here’s a look back at its discoveries

For more than 16 years, the orbiting observatory has revealed wonders of the cosmos

Spitzer galaxy image

In a region 890 light-years across, hundreds of thousands of stars gather around dust clouds in the center of the Milky Way galaxy in this 2006 infrared image from the Spitzer Space Telescope.

JPL-Caltech/NASA, S. Stolovy, SSC

After 16 years and five months in space, NASA’s Spitzer Space Telescope is signing off.

On January 30, engineers will instruct the telescope to power down, bringing an end to one of NASA’s premier orbiting observatories. The telescope’s infrared vision witnessed the births and deaths of stars, charted the Milky Way, found worlds orbiting other suns, spied on comets and planets in our solar system and sought out galaxies in the farthest reaches of the cosmos.

Much of the universe hides behind dust that blocks visible starlight from reaching our eyes. Spitzer’s goal was to knock down those walls. Its detectors are sensitive to infrared light that can penetrate clouds of dust and reveal what lurks beyond. 

“We’re lifting the cosmic veil on the universe,” said former mission manager Suzanne Dodd, a spacecraft operations expert at the Jet Propulsion Laboratory in Pasadena, Calif., at a January 22 NASA TV broadcast reflecting on Spitzer’s accomplishments.

Spitzer launched on August 25, 2003, into an orbit where it trails Earth around the sun (SN: 12/17/03). Named in honor of the late astrophysicist Lyman Spitzer Jr., who in 1946 first proposed putting telescopes in space, the mission originally was planned to operate for just 2½ years. After nearly six years, the telescope ran out of liquid helium needed to keep its instruments ultracold. Spitzer soldiered on, running some of its instruments at a slightly degraded capacity.

“I never had any conception that we would go for 16 years,” said mission scientist Michael Werner, also at JPL, during the same broadcast.

But every day, Spitzer gets farther from home, as a result of the orbit that the satellite is on. At nearly 270 million kilometers from Earth, “it’s becoming more difficult to communicate with the telescope,” said Paul Hertz, director of NASA’s astrophysics division. The space agency also wants to free up resources for its next infrared observatory, the James Webb Space Telescope, scheduled to launch in 2021, Hertz said.

As Spitzer’s mission comes to a close, here’s a look back at some of its images and accomplishments, presented roughly by increasing distance from Earth.

A new ring for Saturn

Saturn already is famous for its gleaming rings. But in 2009, Spitzer first spied the feeble infrared glow of a much larger, tenuous ring encircling the planet (SN: 10/6/09). The ring is 40 times as thick as Saturn and spans a distance over 200 times as wide as the planet itself. The hula hoop of dust appears to be fed by debris knocked off of the moon Phoebe by a steady rain of interplanetary rocks.

Saturn ring
A nearly invisible ring (illustrated) around Saturn was found by the faint infrared light it emits. The infrared image of the planet (shown to scale) was taken at the W.M. Keck Observatory in Hawaii.JPL-Caltech/NASA, R. Hurt/SSC

A septet of Earth-sized worlds

Nearly 40 light-years away, seven Earth-sized planets orbit a dim red star dubbed TRAPPIST-1 — and Spitzer found most of them (SN: 2/22/17). In 2017, astronomers announced that data from Spitzer (with help from observatories on the ground) confirmed two suspected planets and uncovered five more, three of which may be warm enough for liquid water, considered essential for life.

“It’s the best characterized solar system outside of our own,” Werner said.

The TRAPPIST-1 system was not Spitzer’s first foray into exoplanet research. In 2005, the telescope made the first detection of infrared light from planets orbiting other stars. Two years later, astronomers used Spitzer data to create the first temperature map of an entire exoplanet’s atmosphere.

TRAPPIST-1 system illustration
The seven planets of the TRAPPIST-1 system (illustrated) would all fit inside the orbit of Mercury. The coloring marks the habitable zones of the two planetary systems — red is too hot, blue is too cold, and green is just right.JPL-Caltech/NASA
TRAPPIST-1 system illustration
The seven planets of the TRAPPIST-1 system (illustrated) would all fit inside the orbit of Mercury. The coloring marks the habitable zones of the two planetary systems — red is too hot, blue is too cold, and green is just right.JPL-Caltech/NASA

Catching a shooting star      

The star Zeta Ophiuchi, about 370 light-years from Earth, is rocketing through space at nearly 90,000 kilometers per hour. In 2012, Spitzer snapped a series of pictures to create a composite image of this speedy star. Like a boat plowing through water, the star is creating a “bow shock” in the surrounding dust. But unlike a boat, this bow shock is carved out by stellar winds — a steady stream of charged particles from Zeta Ophiuchi — colliding with gas and dust roughly half a light-year ahead of the star.

Zeta Ophiuchi
Winds from the speeding star Zeta Ophiuchi (center) are forming a bow shock in a filament of dust (red) half a light year ahead of the star in this composite image from Spitzer.JPL-Caltech/NASA

Witnessing the birth of stars

Stars are born in dusty cocoons that hide many details of their formation from astronomers — unless they have an infrared telescope. Spitzer allowed researchers to peer through the dust and into the hearts of stellar nurseries throughout the galaxy. At roughly 400 light-years from Earth, the nebula Rho Ophiuchi is one of the closest of these nurseries. With Spitzer, researchers could spy on several hundred stars emerging from the cloud of gas and dust (SN: 2/13/08). Some are still enshrouded in dust, out of which planets may form, while other slightly older stars have shed their dusty cloaks.

Newborn stars
Newborn stars peek out of a veil of dust in this composite image from Spitzer. Color reflects the temperature: Red stars are cooler and still surrounded by dust, while blue stars are warmer and have blown the dust away.JPL-Caltech/NASA, Harvard-Smithsonian Center for Astrophysics

Mapping our galaxy

Much of our galaxy is hidden behind thick lanes of interstellar dust. But that dust was no match for Spitzer, which astronomers used to create an expansive 360-degree infrared map of the Milky Way’s disk (SN: 5/5/14). Known as GLIMPSE360, or the Galactic Legacy Mid-Plane Survey Extraordinaire, the project required over 4,000 hours of telescope time spread across 10 years. With some coverage provided by NASA’s WISE telescope, another infrared observatory in space, the survey has allowed researchers to map out the center of the galaxy, chart its outer limits, trace the Milky Way’s spiral arms and better understand how often the galaxy churns out new stars.

Milky Way infrared map
The center of the galaxy glows bright in this sliver of a 360-degree infrared map of the Milky Way obtained from Spitzer. Blue stars are relatively close to Earth, while red areas mark dusty regions of star formation. The blue haze is light from old stars too far to see individually.JPL-Caltech/NASA, GLIMPSE team

The sombrero’s secret past

When viewed in visible light, the Sombrero galaxy presents a dark outer ring of dust to observers on Earth. In infrared images, the dust lights up the galaxy’s disk, allowing researchers to probe structural details that might otherwise remain hidden. Spitzer images of Sombrero, which lies about 28 million light-years away, revealed that the disk is slightly warped, suggesting a close encounter with another galaxy at some point in the past.

Sombrero galaxy
Dust lanes (red and green) glow with infrared light in this composite image of the Sombrero galaxy from the Spitzer and Hubble space telescopes.Infrared: JPL-Caltech/NASA, R. Kennicutt/Univ. of Ariz., and the SINGS Team; Optical: NASA, Hubble Space Telescope, Hubble Heritage Team

Later analysis of the Spitzer images showed that this galaxy appears to be a hybrid, blending characteristics of disklike galaxies and round elliptical galaxies. One explanation is that perhaps Sombrero might once have been an elliptical galaxy — full of old stars — that got inundated by gas from intergalactic space. The gas, locked in orbit around the galaxy’s center, might have spun out into a flat disk where a new generation of stars was born.

Gazing back in time

In 2005, astronomers were looking for missing quasars, blazing cores of galaxies powered by voracious supermassive black holes. While some quasars had been cataloged, there didn’t appear to be enough to account for a cosmic glow of X-ray light that quasars likely produced. Turns out, they were just hiding. Spitzer images uncovered a cache of quasars lurking within dust-enshrouded centers of galaxies whose light took roughly 10 billion years to reach Earth.

galaxy 10 billion light-years away
The yellow blob in this Spitzer image is a galaxy, roughly 10 billion light-years away, that hosts a dust-enshrouded quasar. The blue and green blobs are galaxies without quasars.JPL-Caltech/NASA, A. Martinez-Sansigre, Oxford Univ.

More recently, astronomers turned Spitzer’s gaze even farther away — and further back in time. In 2011, researchers used Spitzer — along with 11 other telescopes on the ground and in space — to discover the most distant protocluster of galaxies known at the time. Seen as it was just a billion years after the Big Bang, the gathering shows galaxies coming together to form the gargantuan clusters that exist today. And in 2016, astronomers combined the powers of Spitzer and the Hubble Space Telescope to identify what is still the most distant known galaxy. Dubbed GN-z11, its light left the galaxy when the universe, which has been around for 13.8 billion years, was only 400 million years old.

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