Robert Hurt, a visualization scientist working for the Spitzer Space Center, is taking the decommission of NASA’s Spitzer Space Telescope a bit more personally than most.

“Aside from being on the precipice of an emotional breakdown after the loss of something that’s as dear to me as a family member, I'm doing well,” he says.

Even those of us who haven’t spent our careers creating images of the universe from Spitzer data can appreciate the loss. On January 30, NASA’s Spitzer Space Telescope concluded 16 years of infrared observations that allowed scientists to reveal some of the most hidden regions of our universe. With a primary mission of only two-and-a-half years, Spitzer’s small size and efficiency propelled the telescope to exceed scientists’ expectations, revolutionizing our understanding of exoplanets, the composition of planetary systems, and even the earliest star formations.

NGC 1333
NGC 1333 shows the birth of a dense group of stars. Because of the region’s dusty clouds, visible light is obscured and prevents a clear picture. But with Spitzer, scientists use infrared to see through the dust. This gives researchers a better understanding of how sun-like stars begin their lives. “You see a progression of stock stellar ages from young stars, which are well formed and in their teenage years … and then at the other extreme of the sequence, you see stellar infants, which just got out of the crib,” Werner says. “You can imagine a sequence where each generation of stars interacts with the dense cloud of dust and gas, which they're forming to trigger the formation of the next generation of stars.” NASA/JPL-Caltech/R. A. Gutermuth (Harvard-Smithsonian CfA)

But now, as Spitzer’s batteries reach the end of their lives, the telescope is experiencing communication barriers and cooling difficulties. The Spitzer team at NASA and the California Institute of Technology has no choice but to bid the spacecraft farewell.

“Spitzer has fundamentally changed astronomy textbooks,” says Sean Carey, manager of Spitzer’s Science Center at Caltech. “It’s told us so much about the universe in so many different aspects.”

Spitzer, one of NASA’s four “Great Observatories,” launched on August 25, 2003. The telescope cost around $720 million, making it the least expensive of the four Great Observatories launched by NASA in the 1990s and early 2000s. The others include the Hubble Space Telescope, the Compton Gamma Ray Observatory, and the Chandra X-ray Observatory.

Center of Milky Way
Located 26,000 light-years away from Earth, this photo captures the core of the Milky Way galaxy. “Because there's so much dust between us and the center, it was very hard to determine where the center of our galaxy was,” Hurt says. “If our eyes saw those wavelengths of light, you know, 5,000 years ago, we would have had a much better instinct for where we were relative to the rest of everything in our galaxy.” The middle white spot is the center of the galaxy, which marks a supermassive black hole. NASA/JPL-Caltech/S. Stolovy (Spitzer Science Center/Caltech)

Spitzer is unique among these space telescopes because it operates in an orbit revolving around the sun and trailing behind Earth, rather than orbiting our planet. Its distance from Earth and the moon prevents an excess of interference of infrared radiation, the type of light that Spitzer observes, Carey says.

But as Spitzer continues to lag behind Earth, falling farther and farther away, more effort is needed to keep its power running. Eventually, the spacecraft will be on the opposite side of the sun, preventing all forms of communication.

The telescope’s infrared observations are unique from the other Great Observatories, which operate in visible and ultraviolet light (Hubble), X-rays (Chandra), and gamma rays (Compton). Because our sky filters out infrared light, astronomers relied on Spitzer in space to capture the deep corners of the universe. Infrared allows scientists to see objects that are too cold to emit much visible light, as well as regions blocked by dust clouds.

Planetary Nebula
The Helix Nebula is one of only a few dead-star systems where comet survivors are found. These remains are located 700 light-years away and are part of a class of objects called planetary nebulae—leftovers of stars that once resembled the sun. From Spitzer’s infrared view, the white dwarf is seen as a tiny white dot in the middle of the picture. Spitzer also discovered a dusty disk, the bright red circle in the center, which was probably gathered by comets after the death of their star. NASA/JPL-Caltech/K. Su (Univ. of Arizona)

Spitzer’s ability to see cold and distant objects made it handy for tracing the history of the universe. Some of the most distant objects astronomers study can only be seen in infrared due to a phenomenon called redshift. As the universe expands, and light from objects like stars and galaxies travels toward us, those waves of light are stretched, or “redshifted,” into the longer wavelengths of the electromagnetic spectrum, often arriving at Earth (or Spitzer) as infrared light.

“In visible light, we only saw the tip of the iceberg. We only saw the part where the stars had already formed,” Hurt says. “But with Spitzer, we can see the backbone behind all of that.”

As expected, the telescope’s cryogen tanks depleted in 2009, ending Spitzer’s initial five-year “cold phase” which had all three of its science instruments functioning. An extended mission, or “warm phase,” continued to open up windows on the universe as one of the telescope’s cameras endured without cryogenic cooling.

Sombrero Galaxy
Both Spitzer and Hubble worked together to create this image of Messier 104, also known as the Sombrero galaxy. But with only Spitzer’s infrared view, the galaxy, 28 million light-years away, looks less like a sombrero and more like a “bulls’ eye.” Using Spitzer, scientists were able to observe a bright, smooth ring of dust in red. Also, Spitzer detected infrared emission from both the ring and the center of the galaxy, where a black hole lives. Data suggest that the black hole is perhaps a billion times bigger than our sun. Infrared: NASA/JPL-Caltech/R. Kennicutt (University of Arizona) and the SINGS Team

Spitzer was never designed to research exoplanets, or planets that orbit other stars. But because of the telescope’s infrared capabilities, scientists have been able to carry out some of the first significant studies probing the atmospheres of exoplanets, says Michael Werner, a project scientist for the Spitzer Space Telescope at NASA’s Jet Propulsion Laboratory (JPL).

Most notably, in 2017, Spitzer discovered four of the seven planets in the TRAPPIST-1 system, a red dwarf star 40 light-years away. The star is orbited by more Earth-size planets than any other known, and these planets shined at the perfect wavelengths for Spitzer to detect.

Located 12 million light-years away in the Ursa Major constellation, Messier 82's core is a place of rapid stellar birth. By using Spitzer’s three sensitive instruments, scientists can see that the galaxy is surrounded by a huge, hidden cloud of smoky dust. “You can trace the explosion through the infrared emission, which lies above and below the plane of this galaxy,” Werner says. “We see it edge on and it almost looks like the galaxy is on fire.” NASA/JPL-Caltech/C. Engelbracht (University of Arizona)

But the TRAPPIST-1 discovery merely skimmed the surface of Spitzer’s potential. The telescope imaged entire galaxies and star-forming regions, and helped create a groundbreaking 360-degree panorama of the Milky Way galaxy. Spitzer has pioneered the study of hot Jupiters—gas giant exoplanets that orbit close to their stars—and in 2009, found a hidden ring around Saturn. Spitzer measured the mass of stars in distant galaxies, as well as the size of stellar nurseries, where stars are born, and the leftovers from stellar explosions. The telescope’s data has led to over 7,800 published papers, Carey says, a number that will continue to increase even after its decommission.

This image was captured after Spitzer ran out of cryogenic coolant, marking the end of its cold mission. The Orion nebula is often home to colonies of young, hot stars. “Given that Spitzer observes in multiple bands of infrared light … you can completely change the way the nebula looks,” Hurt says. “Every time we look at it … we see something different in the data.” The bright spots in the middle are called the Trapezium cluster, which are the hottest stars in the region. Spitzer keeps track of the young stars and records data as they change. NASA/JPL-Caltech/J. Stauffer (SSC/Caltech)

In 2021, NASA plans to launch the James Webb Space Telescope, a space telescope that will serve as Spitzer’s successor. “People using Webb will be looking at the Spitzer data as a source of targets that they can follow up on right away,” Werner says.

While Webb will be more sensitive, allowing for detailed measurements of the chemical composition and habitability of planets around TRAPPIST-1, it will be bigger and thus less nimble than Spitzer, Carey says. Webb will lack the ability map large fields of the sky efficiently, and while the new telescope will study known objects in unprecedented detail, it won’t be as efficient as discovering unknown and rare objects across the universe.

“When it [Spitzer] stops, there’s going to be a hole in my life and a hole in my heart,” Werner says. “But those holes will be filled in by not only the great scientific results in Spitzer, but by my knowledge and satisfaction in having played a central role in enabling this remarkable facility.”

“There are going to be a lot of tears, and no small number of them will be coming from me,” Hurt says.

“It's been an honor and a privilege,” Carey says. “I just hope that maybe I'll be able to do something as interesting throughout the rest of my career. I'm not sure though. … At some point you peak, and I might have peaked.”

Messier 81 is located 12 million light-years away. It’s visible through binoculars or a small telescope. “What we've done with Spitzer is take images in different parts of the spectrum, which are sensitive to different structures, or processes within the galaxy,” Werner says. “And as we go out into the infrared, we start to see regions where new stars are forming, spread out on those spiral arms like ornaments on a Christmas tree.” NASA/JPL-Caltech
 Swan Nebula
Called the Omega Nebula or the Swan Nebula, this star-making cloud is located 6,000 light-years away from Earth. “These central stars give off intense flows of expanding gas, which rush like river against dense piles of material, carving out the deep pocket at the center of the picture,” according to NASA. NASA/JPL-Caltech/M. Povich (Univ. of Wisconsin)

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