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There's something special about a good space telescope. Think about it: Engineers spend years building and designing it, scientists make their careers analyzing its data, and the rest of us get to come together and marvel at how cool our universe is.

These are pretty amazing machines. But like the humans who build them, space telescopes have a lifespan. They get old and don't work as well (also like us) and eventually, the time comes to call it a day and let another mission take over.

And so yesterday — January 30, 2020 — we had to say goodbye to NASA's Spitzer Space Telescope, which finally gets to retire after spending more than 16 years revolutionizing infrared astronomy. When looking into space, you'll see things different depending on what wavelengths of light you use. The most energetic stuff out there, like black holes, pumps out high-energy light with short wavelengths, so it's best observed by tuning your telescope to detect gamma and X-rays.

At the other end of the spectrum, all of space glows dimly in long-wavelength light. So to study that background radiation, you'll need something like a radio or microwave telescope. But a ton of the universe lives in the in-between:.

It's full of objects too small or cold to produce shorter wavelengths, and too big or warm to be seen well in the longest. Things like planets and ancient galaxies (what astronomers call “the cold, the old, and the dusty”) those are best observed in infrared. Because while many of them don't give off much visible light, they do give off some heat, which is basically what infrared light is.

That's the kind of light Spitzer specialized in. And we built it to be really good at detecting it. The telescope had things like reflective materials and liquid helium, which helped keep its instruments as cold as -267 degrees Celsius — only about three degrees warmer than the background temperature of the universe.

Since colder objects emit less infrared light, that meant Spitzer wouldn't accidentally wash out its own observation with its intrinsic glow. So at the beginning of its mission, it was able to detect the faintest emissions from really cold objects and unreasonably far away objects — like super old galaxies. In 2009, Spitzer's coolant did run out as planned.

But after that, it entered its “warm phase” and kept working at a cozy temperature of about -244 degrees Celsius. Over those two phases and its 16 years, Spitzer gave us tons of insight into the universe and led to some exciting discoveries. We've covered some of them before, like the oldest galaxy ever seen, and the discovery of 5 of the 7 TRAPPIST-1 exoplanets.

That's a planetary system around 40 light-years from here. But there's been a bunch of other cool stuff, too. Like, in 2009, Spitzer discovered that Saturn has a giant ring we didn't know about because it's basically invisible to us.

Its dust particles are so sparse that we can't see them with visible-light telescopes. We can only see their infrared glow. It's called the Phoebe ring, because the moon Phoebe orbits inside it and probably provides a lot of the ring's material.

And it is ridiculously big. From Earth, most of Saturn's rings are really only visible with a telescope. But if the Phoebe ring shined in visible light instead of infrared, you could see it with the naked eye, stretching out wider than two full moons!

This finding didn't just change our view of Saturn, either. It also answered a question we'd been trying to answer for 300 years:. What's going on with Iapetus?

Iapetus is one of Saturn's moons near the Phoebe ring, and it's odd because its leading side is way darker than its other half. The astronomer Cassini noticed this way back in the 1600s, but nobody knew why it happened until we found the Phoebe ring. After that, scientists proposed the moon's coloring is probably because it's gathering dark Phoebe ring material as it orbits, like a car grill gathering bug corpses on the highway.

Of course, Spitzer's impact wasn't just local:. It also gave us an unprecedented view of our galaxy with things like an incredible, 360-degree map of the Milky Way. Finalized in 2014 with over ten years of data, GLIMPSE360 shows a stretch of sky containing about half the stars in the galaxy, which is way more than we can see in visible light.

This is because, in addition to all the stars and stuff out there, there's a bunch of gas that blocks visible light but lets some infrared light through because of its longer wavelength. In fact, this map lets us see clear through to the other side of the Milky Way, and that's allowed astronomers to map out the boundaries of our galaxy with far more accuracy. The data from this map was full of surprises, too:.

It revealed new regions of star formation, and found a lot more carbon in the galactic dust than we'd previously thought. That helps us estimate how many stars are making carbon, dying, and releasing it out into the void. And considering that all life we know of requires carbon… knowing how much life-making material is out there is probably important.

As a whole, the map represents an incredible ten years of science, capturing more than two million of Spitzer's photos in a single image. And it sets us up for the future! Since it will also have some infrared capabilities, the James Webb Space Telescope will be, in some ways, Spitzer's successor.

So when it launches next year, fingers crossed, astronomers will look to the Spitzer map to find the most interesting and fruitful targets. It's always hard to say goodbye to missions, and this time is no exception. But even though Spitzer has gone dark and will spend the future just floating through space, its data will light our way for years to come.

This episode of SciShow Space News is brought to you by the one, the only, SR Foxley, who's this week's President of Space. SR Foxley is one of our patrons on Patreon, and those patrons help us keep diving into the news every week — along with everything else we do on this channel. So thanks for being here, SR!

If you want to learn more about our patron community (including things like our Discord server) you can head over to Patreon.com/SciShow. Our patrons make everything happen around here, and we don't know what we would do without them. [OUTRO ♫].