The Solar Orbiter spacecraft was zipping through space when a "hole" opened up in the sun's atmosphere near its south pole.
It wasn't really a hole, per se. It was a coronal hole — a spot in the sun's outer atmosphere where the temperature has dropped. These "cool" spots don't glow as bright as the rest of the sun, which makes them look black, like a deep hole, in images.
As Solar Orbiter watched the hole, in March 2022, its powerful extreme-ultraviolet instrument spotted something nobody had seen before: teeny tiny flares erupting everywhere.
Look closely at the edge of the sun in the video footage below. One of the small flares protrudes as a dark line from the solar surface:
Scientists couldn't previously detect these mini flares because they're so small — well, on solar scales.
These bright jets of plasma are each a few hundred kilometers long, and disappear after 20 to 100 seconds. Each one emits as much energy as 3,000 to 4,000 US households consume in a year, solar physicist Lakshmi Pradeep Chitta told Nature.
That's nothing compared to the solar flares that scientists are used to. The biggest type of solar eruption is called an X-class flare, which emits the energy equivalent of one billion hydrogen bombs. That's one billion times more energy than the nano-flares at the other end of the spectrum.
The newly discovered flares have 1,000 times less energy than a nanoflare, which is one-trillionth the energy of an X-flare. So scientists call them "picoflares," in a new study of the findings, published in the journal Science on Thursday.
Because these picoflares were all over the coronal hole, the researchers suspect that they're all over the rest of the sun, too.
Picoflares could be the source of the solar wind that's blasting Earth
Picoflares could unlock one of the sun's biggest secrets: how it produces a powerful stream of electrically charged particles and strong magnetic fields, which constantly blasts Earth.
That stream, called the "solar wind," gets supercharged when coronal holes or big solar flares are pointed at our planet. The resulting inundation can block radio signals on Earth, disable power grids, and even push satellites out of orbit.
Scientists want to understand the solar wind so that they can forecast it better, giving Earth more time to prepare for its impacts.
Seeing the sun up close, at smaller scales, could reveal its secrets
Recent findings from NASA's Parker Solar Probe support the idea that constant, previously imperceptible flares could be fueling the solar wind. Those researchers reported other "small-scale jetting activity."
"Jets, in general, have previously been observed in the solar corona," Chitta, who led the Solar Orbiter study and a team at Max Planck Institute for Solar System Research, told Space.com. "The picoflare jets that we observed are the smallest, and energetically the weakest, type of jets in the solar corona that were not observed before."
It's possible that even smaller, more frequent jets we can't see yet are also fueling the solar wind, the European Space Agency reported.
As the sun gets more active, it's a great time to study solar wind
NASA and the ESA launched Solar Orbiter in 2020, with a goal of studying these winds at their source. Someday, scientists hope to better forecast the space weather that comes from the sun.
Now is a great time to study that question, as the sun's activity is building up to the peak of its 11-year cycle. Flares, coronal holes, and other powerful eruptions on the sun are becoming more common.
"Overall now it's a gold mine," Andrei Zhukov, a solar physicist at the Royal Observatory of Belgium in Brussels, who works with Solar Orbiter and co-authored the new study, told Nature.
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