Little by little (or perhaps not so little by little), science is answering questions and solving mysteries about the universe, at least as far as we know. It rains on the sun, that’s the news, but it’s not water. The real chaos lies in the extreme phenomena occurring on its surface and in its atmosphere, phenomena so extreme they defy intuition. One of the most enigmatic is solar rain, a phenomenon in which the sun itself seems to “weep” molten plasma; a phenomenon that has baffled scientists for decades. Now, a team from the University of Hawaii has solved the mystery, and the answer is completely changing our understanding of the atmosphere.
Tens of thousands of degrees, compared to the millions of degrees in the surrounding plasma
To provide some context, this ‘solar storm,’ or rather coronal rain, occurs in the corona, the Sun’s outermost and hottest layer. This discovery, which might seem like a minor detail, forces us to rethink how we understand solar physics and how we model the eruptions that give rise to this phenomenon. The fact is that in these layers of the Sun, masses of denser and relatively “cooler” plasma condense and fall back toward the solar surface, creating bright arcs and loops. Consequently, some areas begin to cool rapidly and form filaments of denser, cooler material that, losing support, fall back toward the surface at high speed. And although we speak of ‘cool,’ the reality is that we’re talking about tens of thousands of degrees, compared to the millions of degrees in the surrounding plasma.
To understand these kinds of phenomena, we need to consider the surrounding context. Scientists realized that solar models predicted this cooling and condensation process should take hours, or even days. However, observations showed that rain formed in a matter of minutes during solar flares. In theory, the plasma should remain hot or cool uniformly, without generating the condensation necessary for plasma droplets to form. The problem is that pre-established models assumed the chemical composition of the corona was static and uniform, a simplification that has undoubtedly led to much worse calculations of the phenomena occurring within the star.
“The lack of rain could be due to an oversimplification in the physics of coronal loop models…”
In fact, in relation to the above, the very article in which this data was published points out that “the lack of rain could be due to an oversimplification in the physics of coronal loop models, with the use of homogeneous and static spatial abundances.” The breakthrough in the research came when scientists introduced into their simulations a factor that had previously been overlooked: the abundance of chemical elements varies in space and time, not statically. The static landscape, or the lack thereof, was the turning point.
The idea is that the composition of the solar atmosphere is dynamic
In summary, the rapid cooling causes a drop in pressure. That is, the change in the amount of certain elements, such as iron, is enough to generate plasma showers that were previously unexplained. Therefore, scientists discovered that at higher density, the cooling becomes even more efficient, resulting in ‘thermal leakage’. The results also show that these changes directly affect radiation. Thus, this model has successfully simulated the formation of rain on the Sun.
Ultimately, the most important takeaway from this study is understanding that the Sun’s atmosphere is not chemically stable; it is constantly changing. The idea that the composition of the solar atmosphere is dynamic, not static, opens up a vast field of research for understanding exactly how energy moves through the star. Therefore, “spacetime abundances are fundamental to understanding plasma cooling in the solar atmosphere and can directly cause coronal rain,” the scientists explain.