The mystery of solar rain solved: the plasma downpour that falls in minutes

Real precipitation occurs on the Sun, but not water: They are incandescent currents of plasma that descend guided by the magnetic field. This phenomenon, known as solar rain, had been puzzling researchers for years due to its rapidity during eruptions.

A team from the University of Hawaii has put order into the puzzle with a work published in The Astrophysical JournalWhere They demonstrate that the chemical composition of the solar corona does not remain fixed., and that detail completely changes the tempo of plasma cooling and condensation.

What is solar rain and why it was surprising

Unlike terrestrial rain, the solar version occurs in the corona, the outermost and very hot layer of the Sun's atmosphere, where small regions of plasma cool abruptly, increase in density, and fall into lower layers at high speed. The puzzling thing was that, instead of taking hours as predicted by classical models, Plasma “droplets” appeared within minutes during eruptions.

Observations with solar probes and telescopes had confirmed this accelerated behavior, but calculations did not reproduce it. The reason, the authors now explain, It is that it was assumed from the start to be homogeneous and invariable in its mixture of elements, a simplification that took its toll when simulating reality.

The missing piece: a crown with changing chemistry

The key breakthrough comes in allowing the abundance of elements varies in space and time within the simulations. By introducing changes in the proportion of elements of low first ionization energy —like iron or silicon—, The model reveals that these areas act as extremely efficient radiators. when they are concentrated at the apex of the coronal loops.

That local excess of heavy elements facilitates a much faster loss of energy through radiation than estimated, which causes the plasma to cool and condense suddenly. According to the team, led by Luke Fushimi Benavitz Along with Jeffrey W. Reep, adjusting the coronal chemistry was the “switch” that allowed the simulation to reproduce what is seen in telescopes.

Step by step: from flash to plasma cascade

It all starts with an eruption that impulsively heats the chromosphere., the layer located under the crown. That heat drives the so-called chromospheric evaporation: dense material rises and fills the magnetic loops of the corona with plasma more similar in composition to that of the photosphere.

Once at the top, the flow concentrates elements such as iron and silicon at the highest point of the loopThis accumulation, due to its great capacity to radiate energy, induces very localized cooling. The pressure drops, the nearby environment provides more plasma, The density increases and thermal instability is triggered, which accelerates the process.: The material condenses and coronal showers begin within minutes.

This chain of events—eruption, evaporation, enrichment in heavy elements, explosive cooling, and collapse—finally fits with the sequences recorded by instruments dedicated to monitoring solar activity. For the authors, It is not an anecdotal byproduct, but a essential dynamic process of the Sun's atmosphere.

Implications for space weather prediction

Understanding when and where these plasma showers form is not just a theoretical triumph. By linking solar showers to the chemistry and dynamics of magnetic loops, The new model offers clues for fine-tuning space weather alerts, essential for protecting satellites, communications, navigation and power grids.

Simulations more faithful to the real behavior of the crown allow better anticipation of the effects of eruptions and coronal mass ejections. In practice, having more precise warning windows can make the difference between a manageable disruption and a costly interruption of critical services.

What's next in solar physics

The study opens the door to mapping, in more detail, how the abundances of elements in the corona evolve over time and how they couple to the changes in the magnetic fieldThe team proposes combining models and observations to track these variations at different scales.

Instruments such as the Solar Dynamics Observatory and missions that are getting closer and closer to the Sun, such as the Parker Solar Probe, can provide real-time data with which to verify and refine these simulations. The goal is Build a unified framework that connects eruptions, coronal chemistry, and plasma fallout with predictive capability.

With this paper signed by Luke Fushimi Benavitz, Jeffrey W. Reep, Lucas A. Tarr, and Andy SH To en The Astrophysical Journal, the community has a coherent explanation for why solar showers emerge so quickly during eruptions. A less uniform corona than previously thought turns out to be the key to understanding that fiery downpour that falls on our star.