The sun’s tenuous upper atmosphere, called the corona, is an ever-changing jungle of sizzling plasma, so creating a map showing the strength of the magnetic fields that largely control that behavior has proven quite difficult to achieve.
Thanks to observations taken with a specialized instrument called a coronagraph that blocks the bright disk of the sun, a team of solar physicists has managed to measure the speed and intensity of the waves that ripple through the coronal plasma.
“This is the first time we have mapped the coronal magnetic field on a large scale,” says Steven Tomczyk, a solar physicist at the High Altitude Observatory in Boulder, Colorado, who also designed the coronagraph.
Theorists had shown decades ago that the velocities of coronal waves can be used to infer the strength of the magnetic field. These waves could also help transport heat from the sun’s surface to the corona; but no one had measured them before in the whole crown.
The magnetic field strength of the corona is mainly between 1 and 4 gauss , a few times the strength of the Earth’s magnetic field at the planet’s surface, so mapping is quite a milestone.
“The solar magnetic field is evolving all the time,” says Zihao Yang of Peking University in Beijing. Sometimes the sun releases magnetic energy explosively, sending blasts of plasma that can shoot into space. Those ejections can wreak havoc on satellites or power grids when they hit Earth. Continuous monitoring of coronal magnetism could help predict such bursts.
Researchers are already working on an improved version of the coronagraph, called COSMO , for the Coronal Solar Magnetism Observatory , which would use the same technique repeatedly with the ultimate goal of predicting the behavior of our star. “The goal is to do it regularly, to do it all the time,” say the authors.
Reference: Z. Yang el al., “Global maps of the magnetic field in the solar corona,” Science (2020). science.sciencemag.org/cgi/doi… 1126 / science.abb4462
