It rains on the Sun, and scientists at the University of Hawaiʻi Institute for Astronomy (IfA) have finally uncovered the reason why.

Unlike the water droplets that fall on Earth, solar rain occurs within the Sun’s corona, a region of extremely hot plasma that extends above its surface. This phenomenon involves cooler, denser clumps of plasma that condense high in the corona and then descend back toward the Sun. For years, researchers struggled to understand how this process could happen so rapidly during solar flares.

New explanation
Now, that long-standing mystery has been solved by Luke Benavitz, a first-year graduate student at IfA, and astronomer Jeffrey Reep. Their findings, published in the Astrophysical Journal, provide an essential update to solar models that have puzzled scientists for decades.

“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. “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.”