[ INTRO] One of the perks of being an astronomer is getting to use amazing technology  in even more amazing places.

Some of the world’s most important observatories are located on remote islands,  high deserts, and even Antarctica. And there’s one telescope whose “WOW”  factor might just overshadow the rest.

The Stratospheric Observatory  for Infrared Astronomy, or SOFIA, features a telescope larger than Hubble mounted inside a Boeing 747SP  aircraft. It’s a telescope that flies. But after twelve years of science,  its mission has come to an end.

So let’s look back to see why  something like this ever existed, what it contributed to our  understanding of the cosmos, and what finally did it in. As an infrared telescope, SOFIA observed the universe through a super  handy part of the electromagnetic spectrum. For example, it’s used to study things  that are a lot cooler than stars, like planets and asteroids.

They aren’t hot enough to radiate  much of their own visible light, but they do shine in invisible  infrared wavelengths. And infrared light can do  what visible light can’t. It can pass through the huge clouds  of dust that litter the galaxy, enabling astronomers to see  what’s hiding behind them.

But infrared astronomy does  have one giant drawback: most of its wavelengths, and  especially the longest ones, get absorbed by molecules in Earth’s atmosphere. Like water vapor and carbon dioxide. So while there are some ground-based telescopes that study the universe in infrared,  astronomers usually want to get these telescopes as far above the atmosphere as possible.

The obvious place to go is into space, but it’s hard to overstate just  how expensive space telescopes are to build, launch, and operate. But what if there’s a way to split the difference? What if you mount your telescope inside a plane?

It’s such a clever idea that SOFIA  wasn’t even the first attempt. Its predecessor, the Kuiper Airborne Observatory, operated from 1975 to 1995. But when SOFIA started its  preliminary science mission   in 2010, it took the concept to the next level.

Developed by NASA and the German Aerospace Center, SOFIA could cruise up to an  altitude of 13.7 kilometers, above more than 99% of the  atmosphere’s water vapor. And from that height, SOFIA was able to  make some groundbreaking discoveries. It made the first observation of helium hydride, which scientists believe may have been the  first molecule to form after the Big Bang.

And it helped uncover how even more  complex molecules may have emerged… like the building blocks of life. Stellar nurseries like the Iris Nebula are  home to baby stars in a sea of gas, dust, and complex organic molecules. And as they form, those stars emit  a lot of ultraviolet radiation.

So the question astronomers had  was whether all that UV light was in the process of breaking these organic  molecules down, or helping to build them up. By using infrared light to track  where different organic compounds were located in the Iris Nebula, SOFIA showed  that it was actually a little bit of both. The closer these compounds are to a star,  where the UV radiation is more intense, the bigger they tend to be.

So while some smaller organic molecules  are probably getting destroyed, this result suggests the ultraviolet  light from these baby stars is also helping them combine  into larger compounds. And one day, those could go on to  jumpstart the evolution of life. SOFIA also helped reveal  the lives of galaxies, too.

It turns out, magnetic fields can play  an important role in feeding or starving the supermassive black hole  at the center of a galaxy. When SOFIA studied the core  of a galaxy dubbed Cygnus A, it found powerful magnetic fields trapping  matter near its central supermassive black hole. That allowed the black hole’s  gravity to continuously draw that matter into its proverbial mouth,  resulting in an active galactic nucleus.

As all that available matter spirals downward, it heats up so much the resulting light  can outshine all the stars in the galaxy. But when SOFIA set its sights on the black  hole in the center of our own galaxy, it observed the opposite effect. Instead  of providing a never-ending feast, the magnetic field appears to be directing  material away from our supermassive black hole, putting it just out of reach in a stable orbit.

But not all of SOFIA’s discoveries are so cosmic. The observatory has made some big  contributions closer to home, too. Like in 2020, SOFIA confirmed that  the Moon’s surface contains water… outside the craters where sunlight can’t reach.

There were a few other studies  that hinted this was true. Basically, there was one particular wavelength of infrared  light that looked like it was being absorbed, which would happen if there were water  molecules there to do the absorbing. But that light could also be absorbed  by compounds with hydroxide in them.

That’s O-H. Not H2O. So the  results were inconclusive.

SOFIA was able to draw that conclusion because  it had access to longer infrared wavelengths, allowing it to look for a signal that water  molecules emit, but hydroxide compounds don't. So, with all of those discoveries, why is SOFIA being retired well before  the end of its initial 20-year mission? Every ten years, the astronomical community  convenes to write a report for NASA that lays out a roadmap for  the next decade of exploration.

And the 2020 version of that report  claimed that SOFIA’s unique abilities did not align with the research questions  they wanted to focus on answering. In addition, SOFIA supposedly hadn’t   produced enough scientific papers  given what it cost to operate. Which is a huge bummer, because now  there are no telescopes in operation   that can study the universe in the far infrared.

Not even the mighty James Webb  Space Telescope can do that. Despite the outcome, SOFIA is a  monument to scientific ingenuity. If you’ve ever tried to take a good  photo out the window of an airplane,   you understand the challenges the project faced.

It might not have worked out as  well as scientists had hoped, but it was a heck of a cool idea. So thanks to SOFIA for all of the discoveries. Thanks to all the engineers, scientists,  and flight crew that kept SOFIA running   over all these years.

And thanks to all of our  patrons, who help keep this channel running. If you’d like to learn how  you can support SciShow Space, head on over to patreon.com/scishowspace. [ outro ]