Researchers at the University of Hawaiʻi Institute for Astronomy have solved the mystery of why solar rain forms so quickly during solar flares. Their work reveals that changing elemental abundances, like iron, enable the rapid cooling of plasma in the Sun's corona. This breakthrough could enhance predictions of space weather impacts on Earth.
Solar rain, consisting of cooler, heavier blobs of plasma, occurs in the Sun's corona—the outermost layer of intensely hot plasma—where these blobs condense high above the surface and plunge back down. For years, scientists puzzled over how this phenomenon forms rapidly during solar flares, as earlier models predicted the necessary heating and cooling would take hours or days, not minutes.
Luke Benavitz, a first-year graduate student at the University of Hawaiʻi Institute for Astronomy (IfA), along with IfA astronomer Jeffrey Reep and colleagues Lucas A. Tarr and Andy S.H. To, addressed this gap in their study published in the Astrophysical Journal in 2025. Titled 'Spatiotemporal Low First Ionization Potential Abundance: A Catalyst for Coronal Condensation,' the paper (volume 992, issue 1, article 4; DOI: 10.3847/1538-4357/ae019d) shows that time-varying elemental abundances explain the quick formation.
"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," Benavitz said. "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."
This discovery overturns decades-old assumptions of constant atmospheric composition, prompting a reevaluation of solar heating processes. "This discovery matters because it helps us understand how the Sun really works," Reep explained. "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."
The findings provide better tools for simulating solar flares, potentially improving forecasts of space weather events that affect Earth's technology and communications.