The Sun's Puzzling Heating Problem Is Closer to Being Solved

At 10,000 degrees Fahrenheit, the sun's surface seems like it would be one of the hottest places in our solar system. But in the outermost layer of its atmosphere called the corona, temperatures can reach 100 times higher. Why? That's a mystery that has puzzled scientists for decades. It's known as the coronal heating problem.

Using a supercomputer, astrophysicists have been able to reconcile two of the major theories for the corona's extreme heat and show they match up neatly with observations taken by NASA's Parker Solar Probe, a tiny robot that recently became the first spacecraft to "touch the sun."

Their study, published Thursday in the journal Nature Astronomy, uses a six-dimensional simulation of a small patch of the sun's corona to analyze how particles are heated up and how they interact with the mammoth furnace's magnetic fields. 

"What is nice about our result is that it links together two previous theories that had each been very well studied," said Jonathan Squire, an astrophysicist at the University of Otago in New Zealand. The theories revolve around "turbulence," which heats up the corona by transferring energy from close to the sun outward, and a type of magnetic wave known as "ion cyclotron waves." The theories both have holes that don't line up with observations made by spacecraft and telescopes. They struggle to explain how the corona can get so hot on their own.

So Squire and his co-authors basically shrugged their shoulders and asked: "Well, why don't we have both?"

The computer simulations they performed show that turbulence drives the ion cyclotron waves, "which effectively keeps the "good bits" of both of the theories individually," according to Squire.

Though the team didn't directly use data from NASA's Solar Probe in this paper, it did provide a point of comparison and its data seemed to match what the sun simulation spat out, giving the researchers confidence in their simulations. This doesn't necessarily mean the "coronal heating problem" is solved, but Squire said the team has made important progress in understanding the phenomenon.

He points out that "there may be multiple different mechanisms operating in different parts of the sun" and different mechanisms could be heating the corona in different ways. 

While all this seems like a problem that's 100 million miles away from home, the corona -- and the solar wind that blasts out of the sun -- can wreak havoc on Earth. They send particles blazing across space that can cause geomagnetic storms, messing with our planet's magnetic field and disrupting satellites.

In early February, a batch of recently launched SpaceX Starlink satellites were doomed after a geomagnetic storm hit them just after launch, preventing the broadband satellites from reaching their desired orbit. They eventually came crashing back to Earth, burning up in the atmosphere.

Squire said the reason those storms are so violent must be related to the ways in which the corona and solar wind heats up. Indirectly, turbulence and ion cyclotron waves might one day take out your internet -- unless we can see them coming.

"In order to have better predictions for space weather and geomagnetic storms," Squire said, "we have to understand more about how the corona works."