The Corona Is Unexpectedly Hot – Parker Solar Probe Eliminates One Theory

Eddie Gonzales Jr. – MessageToEagle.com – The sun’s crown-like atmosphere can be 200 times hotter than its surface, despite being farther from the core’s heat source.

By diving into the sun’s corona, NASA’s Parker Solar Probe has ruled out S-shaped bends in the sun’s magnetic field as a cause of the corona’s searing temperatures, according to University of Michigan research.

As Parker Solar Probe files around the sun, it finds abrupt reversals in the direction of the sun’s magnetic fields. These S-shaped bends in the sun’s magnetic field are very common in the solar wind close to the sun, but are absent inside the corona. Image credit: Adriana Manrique Gutierrez, NASA’s Goddard Space Flight Center.

How the corona’s heat seemingly defies physics has stumped scientists for decades, yet it allows the sun’s hot soup of charged particles, or plasma, to move fast enough to escape the sun’s gravitational pull and engulf our solar system as the solar wind.

NASA built the Parker Solar Probe to investigate the corona’s heat source. The spacecraft carries instruments designed by U-M professor Justin Kasper to measure the corona’s plasma density, temperature, and flow.

As it neared the sun, the probe detected hundreds of S-shaped “switchbacks” that briefly reverse the magnetic field’s direction, along with thousands of shallower bends.

Some scientists view switchbacks as potential heat sources for the corona and solar wind. Their S-shaped bends store significant magnetic energy, which likely releases into surrounding plasma as the switchbacks travel and straighten.

NASA sent Parker Solar Probe into the sun to learn how its atmosphere is hotter than its surface. Image credit: Applied Physics Lab and NASA Goddard Space Flight Center.

“That energy has to go somewhere, and it could be contributing to heating the corona and accelerating the solar wind,” Mojtaba Akhavan-Tafti, U-M assistant research scientist of climate and space sciences and engineering and the corresponding author of the study, said in a press release.

But to heat the corona, switchbacks need to move through it, so learning where switchbacks form is critical for understanding their influence on the corona’s temperature. After poring over the data from the Parker Solar Probe’s first 14 laps around the sun, the research team discovered that while the S-shaped bends are common in the solar wind near the sun, they are absent inside the corona.

Scientists still can’t agree on what causes switchbacks. Some think that the magnetic field is bent by turbulence in the solar wind beyond the corona. Others think that switchbacks start their journey at the surface of the sun, when churning magnetic field lines and loops explosively collide and combine into bent shapes.

The study’s results rule out the latter hypothesis. If switchbacks were formed by colliding magnetic fields at the surface of the sun, they ought to be even more common inside the corona. However, Akhavan-Tafti thinks magnetic collisions could still play some indirect role in the origins of switchbacks — and the heating of the corona.

“Our theory could fill the gap between the two schools of thought on S-shaped switchback generation mechanisms,” Akhavan-Tafti said. “While they must be formed outside the corona, there could be a trigger mechanism inside the corona that causes switchbacks to form in the solar wind.”

When magnetic fields collide at the sun’s surface, they vibrate like plucked guitar strings and send waves along the magnetic fields into space. At the same time, the energy from the collisions creates very fast streams of plasma in the solar wind.

Akhavan-Tafti thinks the fast plasma distorts the magnetic waves into switchbacks in the solar wind. If some of those waves dissipate inside the solar atmosphere before becoming switchbacks, they could also play a part in heating the corona.

“The mechanisms that cause the formation of switchbacks, and the switchbacks themselves, could heat both the corona and the solar wind,” he said.

There currently isn’t enough data to favor triggers at the sun’s surface over turbulence in the solar wind as the cause of switchbacks, however.

“Parker Solar Probe’s upcoming trips into the sun, as early as December 24, 2024, will collect more data even closer to the sun. We will use the data to further test our hypothesis,” Akhavan-Tafti said.

Paper: M. Akhavan-Tafti, S. L. Soni. In Situ Mechanisms are Necessary for Switchback Formation. The Astrophysical Journal Letters, 2024; 970 (2): L26 DOI: 10.3847/2041-8213/ad60bc

Written by Eddie Gonzales  Jr. – MessageToEagle.com Staff Writer