Say goodnight, Spitzer. Farewell to a groundbreaking space telescope.

The mission was only supposed to last for 2 1/2 years. But, more than 16 years later, NASA’s Spitzer Space Telescope has far exceeded expectations. 

Since launching in August 2003, Spitzer has facilitated discoveries that its designers never imagined. Peering at the universe in the infrared, the space telescope has unveiled stellar nurseries, spotted the most distant galaxies, and revealed the contents of exoplanet atmospheres. But on Thursday, Jan. 30, engineers are signaling to Spitzer to power down, as NASA shifts resources toward the impending launch of its successor, the James Webb Space Telescope.

With wavelengths longer than those of visible light, infrared radiation is invisible to the naked eye, but not to Spitzer. As such, the space telescope scanned parts of the cosmos that were long obscured from view.

When it came to infrared astronomy, Spitzer did it all. It was sort of like a Swiss Army knife of telescopes. It looked past the visible at everything near and very, very far. It examined the cold side of the cosmos, and thus opened the door to a whole new view of the universe and its origins. Spitzer’s story is one of what happens when we probe deeper, looking beyond the visible.

“Spitzer Space Telescope has unveiled the infrared universe,” Farisa Morales, an astronomer at NASA's Jet Propulsion Laboratory, said during a NASA event celebrating Spitzer last week. “It has allowed us to see what our human eyes could not see.”

NASA

Towering pillars of dust are aglow with the light of embryonic stars (white/yellow) in this Spitzer Space Telescope image of a region dubbed "Mountains of Creation."

Spitzer was part of a team of four space telescopes, including the Hubble Space Telescope, Compton Gamma Ray Observatory, and Chandra X-ray Observatory. Together, they were dubbed NASA’s Great Observatories. The idea was that each one would study a different part of the electromagnetic spectrum, and together they would give scientists a much more complete view of the cosmos.

“The visible is really a tiny fraction of the signals that we could detect. Of course it’s the signal we’re most familiar with, but it’s a very small part of the electromagnetic spectrum,” says Pauline Barmby, an astrophysicist at Western University in Ontario. 

Different kinds of astronomical phenomena radiate across parts of the electromagnetic spectrum. Infrared radiation often comes from “the cold, the old, and the dusty,” as Spitzer scientists like to say. 

Not all objects in space glow hot enough to give off visible light, but all objects in space do emit infrared radiation. So Spitzer homed in on some colder objects – like nebula and brown dwarfs – to see what optical astronomy had been missing. Like night vision goggles, the space telescope also peers through dust for heat signatures of objects obscured from optical view. 

If you’ve ever looked at the Milky Way in a truly dark, clear night sky, you know that there’s a lot of dust and gas blocking the visible light of many stars. So Spitzer also turned its infrared “eyes” on our own galaxy. It snapped enough pictures for scientists to stitch together one of the most extensive maps of the Milky Way.

Because Spitzer could glimpse what was invisible to optical telescopes, it also revealed some surprises. For example, Spitzer data revealed that Saturn’s rings are even more extensive than previously thought. The space telescope spotted a wispy ring around the planet that hadn’t been detected before – and it’s huge. It’s about 170 times wider and 20 times thicker than the diameter of Saturn. 

NASA

Scientists using the Spitzer Space Telescope and ground-based telescopes discovered that there are seven Earth-size planets in the TRAPPIST-1 star system. Under the right atmospheric conditions, all seven could have liquid water – key to life as we know it – but the chances are highest with the three in the habitable zone.

“[Spitzer has] done so much. It’s done some things that we sort of expected based on the design,” says Sean Carey, manager of the Spitzer Science Center at the California Institute of Technology. “And then we took off and just crushed the original science goals.”

One of Spitzer’s greatest legacies wasn’t in the original plan. When the space telescope launched, exoplanet science was just getting going. But, as Spitzer was built to add a new lens on the most intriguing parts of the cosmos, gathering data on exoplanets quickly became part of its repertoire. 

It turned out, infrared astronomy was particularly useful for studying exoplanets. Spitzer was the first to capture light directly from an exoplanet, opening the door to much more intensive study of the distant worlds.

One of the most famous exoplanet discoveries of the last decade – the TRAPPIST-1 system, where seven Earth-size planets orbit a single star just 40 light years away – is also a feather in Spitzer’s cap. After optical telescopes spotted a few planets orbiting that star, researchers realized that it was a job for an infrared observatory because it is quite cooler than the sun. Spitzer observed the TRAPPIST-1 system for more than 500 hours to count its planets. 

“This little facility that was never designed to study planets beyond our solar system, it totally changed the paradigm for that field in just a few short years,” says Nikole Lewis, an astrophysicist at Cornell University and a member of the Spitzer oversight committee.

Now the Spitzer-trained astronomers are gearing up to take infrared observations to the next level. The much-awaited James Webb Space Telescope is currently planned to launch next year and will build on Spitzer’s legacy.

At about 1,000 times more powerful than Spitzer, says Amber Straughn, an astrophysicist at NASA and deputy project scientist for James Webb Space Telescope science communications, James Webb will bring the most distant galaxies into much sharper resolution. The goal, she adds, is to use James Webb to find the very first galaxies formed after the Big Bang – and, of course, to get a better look at exoplanets, too.

For many scientists connected to Spitzer, this is the end of an era, personally.

“It’s like this companion that has been with me for a big fraction of my career,” says Dr. Barmby. “I think we are all feeling a little bit melancholy, when we’re not in a panic to write our plans to use James Webb.”