A team of more than 1,000 astronomers and college students just took a step closer to solving one of the long-lasting mysteries of astronomy: Why is the sun’s outer layer, known as the corona, so ridiculously hot? The solar surface is 10,000°F, but a thousand miles up, the sun’s corona flares hundreds of times hotter. It’s like walking across the room to escape an overzealous space heater, but you feel warmer far away from the source instead of cooler, totally contrary to expectations.

The research team used hundreds of observations of solar flares—huge ejections of hot plasma from our star’s surface—to determine what’s heating up the sun’s corona, in results published May 9 in The Astrophysical Journal. What’s really striking about this result, though, is how they did it: with the help of hundreds of undergrads taking physics classes at the University of Colorado, totaling a whopping 56,000 hours of work over multiple years.

Lead author James Paul Mason, research scientist and engineer at the Johns Hopkins Applied Physics Laboratory, calls this a “win-win-win scenario.” He adds, “We were able to harness a ton of brainpower and apply it to a real scientific challenge, the students got to learn firsthand what the scientific process looks like.”

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The classroom project began in 2020, when University of Colorado physics professor Heather Lewandowski found herself teaching a class on experimental physics, which suddenly had to pivot online due to the COVID-19 pandemic—quite the challenge, especially for a hands-on science course. Luckily, Mason had an idea for a solar flare project that needed a lot of hands, and Lewandowski, who usually researches a totally different topic in quantum mechanics, saw that as an opportunity for her students. 

“The question of why the sun’s corona is so much hotter than the ‘surface’ of the sun is one of the main outstanding questions in solar physics,” says Lewandowski. There are two leading explanations for this dilemma, known as the coronal heating problem. One theory suggests that waves in the sun’s mega-sized magnetic field push heat into the corona. The other claims that small, unseen solar flares called nanoflares heat it up, like using a thousand matches instead of one big blow torch. 

Nanoflares are too small for our telescopes to spot, but by studying the sizes of other larger flares, scientists can estimate the prevalence of these little radiation bursts. And, although artificial intelligence is improving every day, automated programs can’t yet do the kind of analysis that Mason and Lewandowski needed. Groups of students in Lewandowski’s class each used data on a different solar flare, getting into nitty-gritty detail to measure how much energy each one dumped into the corona. Together, their results suggest nanoflares might not be powerful enough to heat up the corona to the wild temperatures we see.

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The scientific result is only half of the news, though. Lewandowski and Mason pioneered a new way to bring real research into the classroom, giving students a way to not only learn about science, but do it themselves. This type of large-scale student research effort is more common in biology and chemistry, but was pretty much unheard of in physics—until now. “The students participated in all aspects of the research from literature review, meetings with the principal investigator, a proposal phase, data analysis, and peer review of their analysis,” says Lewandowski. The involvement of many students, and their work in groups, is also a reminder that “science is inherently a collaborative endeavor,” she adds.

“I hope that we inspire some professors out there to try this with their classes,” says Mason. “I’m excited to see what kinds of results they’re able to achieve.”