UH researchers crack solar rain mystery

It rains on the Sun, and thanks to researchers at the University of Hawaiʻi Institute for Astronomy (IfA), we finally know why.

Unlike water that falls from the sky on Earth, solar rain happens in the Sun’s corona, a region of super-hot plasma above its surface. This rain consists of cooler, denser blobs of plasma that fall back down after forming high in the coronae. For decades, scientists struggled to explain how this rain forms so quickly during solar flares.

New explanation

That mystery was cracked by Luke Benavitz, a first-year graduate student at IfA, and IfA astronomer Jeffrey Reep. Their work, recently published in the Astrophysical Journal, adds a missing piece to decades of solar models.

“At present, models assume that the distribution of various elements in the corona is constant throughout space and time, which clearly isn’t the case,” said Benavitz in a UH news release. “It’s exciting to see that when we allow elements like iron to change with time, the models finally match what we actually observe on the Sun. It makes the physics come alive in a way that feels real.”

Why it matters

The new finding means solar scientists can better model how the Sun behaves during flares, insights that could one day help predict space weather that affects our daily lives. 

Earlier models required heating over hours or days to explain coronal rain; however, solar flares can happen in just minutes. The IfA team’s work shows that shifting elemental abundances can explain how rain can quickly form.

“This discovery matters because it helps us understand how the Sun really works,” said Reep. “We can’t directly see the heating process, so we use cooling as a proxy. But if our models haven’t treated abundances properly, the cooling time has likely been overestimated. We might need to go back to the drawing board on coronal heating, so there’s a lot of new and exciting work to be done.”

Fresh insights

This research opens the door to a much wider range of questions. Scientists now know that elemental abundances in the Sun’s atmosphere should change over time, which challenges long-standing models that assumed they were fixed. This means the discovery reaches far beyond coronal rain, pushing researchers to rethink how the Sun’s outer layers behave and how energy moves through its atmosphere.