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The International Ultraviolet Explorer was the first of its kind, giving us glimpses into phenomena like supernovas and Halley's comet. So why do we hear so little about it?"

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Sources:

https://www.esa.int/Science_Exploration/Space_Science/IUE_overview
https://science.nasa.gov/missions/iue
http://adsabs.harvard.edu/full/1998ESASP.413...37H
https://sci.esa.int/web/iue/-/31290-science-results
https://swift.gsfc.nasa.gov/about_swift/uvot_desc.html
https://asd.gsfc.nasa.gov/archive/mwmw/mmw_across.html
https://www.nasa.gov/feature/goddard/2018/astronomers-release-most-complete-UV-survey-of-nearby-galaxies
https://sci.esa.int/web/iue/-/31297-archive
https://www.nytimes.com/1986/12/04/us/orbiting-observatory-sights-ice-blast-on-halley-s-comet.html
https://www.latimes.com/archives/la-xpm-1986-12-07-mn-1459-story.html
https://www.eso.org/sci/publications/messenger/archive/no.15-dec78/messenger-no15-27-31.pdf
[intro].

There are a few names that reverberate  in the pantheon of famous space missions, like Hubble, Voyager 1 & 2, and the Space  Shuttle Missions, from Enterprise to Endeavor. But another name you might want  to start including in that list is the International Ultraviolet Explorer, or IUE.

It launched in 1978 to study  the ultraviolet universe, and it was so effective and reliable that  it worked 24 hours a day, 7 days a week, for almost 19 years. The IUE had unprecedented  flexibility for a space telescope, and that allowed it to make  some major discoveries — including capturing the biggest,  closest supernova in centuries. Many popular telescopes study  the universe in visible light, but that really only gives us one perspective.

Astronomical phenomena can  emit multiple types of light, and each can teach us something different. For instance, cooler stars tend  to glow mostly in infrared. But younger, hotter, and more massive  stars tend to peak in the ultraviolet.

Supernovas also shine really brightly in UV. So, if you could observe that ultraviolet light, you could learn more about how  stars form, develop, and die. Unfortunately, our atmosphere is really  good at absorbing ultraviolet light.

And while that’s great for our skin, it  also makes it hard to study UV from Earth. So if you want to see this side of the universe,  you have to send your instruments to space. We started doing this in the late 1940s, and had flown several UV missions  by the late ‘60s and early ‘70s.

But none of them rivaled the  International Ultraviolet Explorer. NASA, the European Space Agency, and the UK all collaborated on the mission, and in 1978 they launched it  into a special kind of orbit. It was a geosynchronous orbit, meaning it traveled fast enough  to keep up with Earth’s rotation.   So it always floated above the same spot — in this case, the Atlantic Ocean.

And that was huge. In fact, the IUE was the  first astronomical research   satellite to be placed in this kind of orbit, because they’re not easy to get to. With how the math works out,  if you want your satellite to take a long time orbiting Earth, you  have to get it farther from the planet.

So, here, to get an orbit 24 hours long, your satellite has to be  some 30,000 kilometers away. That’s almost 90 times farther  than the Space Station! And it means you need a lot of fuel,  and that your satellite has  to be light and compact.

But the payoff was worth it. Because of this orbit, the IUE was  always in sight of ground stations on both sides of the ocean, in the US and Spain. That meant someone could  operate it 24 hours a day.

And that allowed observations  to be made in real-time, which was a new and exciting  ability for a space telescope. Most other telescopes are in orbits  where they move relative to the ground. So they have windows of time where astronomers  can download their data and give commands, and other windows where the  telescopes are busy observing things.

During those times, they can’t be disturbed, even if there’s something really  interesting happening elsewhere in the sky. But IUE could be in constant  communication with the ground, so if another telescope spotted something cool,   it could follow up with UV  observations within an hour or two. Like if, say, a star exploded in the  brightest supernova in almost 400 years.

That happened in 1987. And because we  could point the IUE toward it so quickly, we got to catch a supernova exploding for  the first time with a modern telescope. Because of this, we learned that the  culprit was an exploding blue supergiant — not one of the more common red ones,  like scientists might have guessed.

And further analyses of the explosion’s  light, plus some help from other satellites,   also confirmed an idea  scientists had held for a while: that supernovas, with all their  intense pressures and temperatures, are responsible for creating most  of the heavy elements on Earth! And that’s really only the tip  of the iceberg with this mission. Like, earlier, in 1986, IUE  studied the famous Halley’s comet along with a fleet of other telescopes.

And its ultraviolet perspective caught a bunch  of carbon dioxide ions flying off the comet. To explain this, researchers  proposed that comets like this don’t have homogeneous internal structures:. Instead, they might have occasional,  internal pockets of volatile compounds.

And when those compounds heat up  as the comet approaches the Sun, they might explode outward. The pocket in Halley’s comet  didn’t realize a lot of material — the IUE only detected about three cubic  meters’ worth. So overall, the comet is fine!

But in other cases, the lead researcher  here proposed that this mechanism could be enough to destroy a comet altogether. Over its years in operation, the IUE  took more than 100,000 observations of almost 10,000 objects, including  stars, comets, and galaxies. They’ve taught us how much stuff there  is in the space between galaxies, that Jupiter has auroras, and how fast  comets lose water as they approach the Sun.

It’s a varied list, because UV light  lets you study that many phenomena! And for most of its lifetime, the IUE was our only  way to observe ultraviolet light in the universe. So, maybe unsurprisingly, thousands of research papers and more than 250  PhD projects have used data from the telescope, making it foundational to an  entire generation of astronomers.

Eventually, though, the  telescope started to wear out. And with budget constraints and broken parts  leading to increasingly complicated operations, the team decided to end the  mission in September 1996. Today, it’s been succeeded by things like the UV  cameras on the Hubble and the Swift satellites.

But overall, the IUE really laid the  foundation for both modern UV astronomy and for long-lived international collaborations. So the next time you’re listing off your  favorite missions, consider this one, too. And if you really want to show  your love for this mission — hey, we made a pin!

The IUE is our pin of the month  for January, so all month long, you can order one of these to attach to  your favorite jean jacket, hat, backpack, or whatever else! Besides just being beautiful to look at,  they’re also an excellent conversation-starter. If you want one, you can head  over to DFTBA.com/SciShow any time between now and February 1st.

Thanks! [ outro ].