Astronomers have detected “Plasma Rain” pours over the solar surface, and it explains why the sun’s outer atmosphere is hotter than the other stars.
NASA revealed coronal rain in a smaller kind of magnetic loop on the sun, according to a statement this rain contains large droplets of hot plasma that fall from the sun’s outer atmosphere down toward the star’s surface.
Compared to rain on Earth, the plasma rain on the sun is millions of degrees Fahrenheit hotter. Also, it is electrically charged gas and doesn’t pool like water on Earth. But the plasma traces the magnetic field lines, or loops, that emerge from the sun’s surface.
In addition, the researchers found that plasma, where the magnetic loops attach to the sun’s surface, is superheated, reaching over 1.8 million degrees Fahrenheit (1 million degrees Celsius). This superhot plasma expands up the loop and gathers at the structure’s peak. As the plasma cools, it condenses, and gravity pulls it back down the loop, creating coronal rain, according to the statement.
Previously, researchers had been searching for signs of rain in larger, closed-magnetic-loop features known as helmet streamers, which extend miles from the sun’s surface. Researchers targeted these because the streamers believed to be one source of the slow solar wind.
Therefore, the researchers’ find The Astrophysical Journal Letters, shed light on the source of the slow solar wind, as well as the heating process of the corona.
“If a loop has coronal rain on it, that means that the bottom 10% of it, or less, is where coronal heating is happening,” Emily Mason, co-author of the study and a graduate student at The Catholic University of America in Washington, D.C., said in the statement.
The researchers identified raining loops that were about 30,000 miles (48,000 kilometers) high — a mere 2% the height of some of the helmet streamers the team originally sought, according to the statement.
“We still don’t know exactly what’s heating the corona, but we know it has to happen in this layer,” Mason said.
The new findings also identified a possible link between the smaller magnetic loops and slow solar wind. Specifically, the team’s observations show that coronal rain can also develop on open magnetic field lines, rather than only closed loops, as researchers had previously thought. One end of these open magnetic field lines lead out into space, where plasma could escape into the solar wind, according to the statement.
The researchers plan to study the smaller magnetic loop structures further using NASA’s Parker Solar Probe, which launched in 2018 and has already traveled closer to the sun than any other spacecraft.