The sun likes to remind us that Earth is merely one part of a joined system. It has ultraviolet rays that can burn our skin and eyes and even drive extinction. Its light can disappear altogether during a solar eclipse and it hurls twisty and tangled solar flares and coronal mass ejections full of plasma at us. Despite our cosmic connection with the sun, there are still numerous scientific mysteries to unravel about this critical star, particularly its magnetic field.
“The sun is not just off in some void of space that we’re not connected to,” Sarah Gibson, a heliophysicist at the National Science Foundation National Center for Atmospheric Research (NCAR) in Colorado, tells Popular Science. “The aurora is actually showing us that direct connection. We’re connected to what’s going on the sun through light, and ultimately, through magnetic fields.”
Now, for the first time, scientists have taken nearly daily measurements of the sun’s coronal magnetic field. This critical spot had only been observed in irregular increments and this new observation offers a more dynamic view of this solar region. With it, we could learn more about what drives intense solar storms that can impact fundamental technologies here on Earth. The findings are detailed in a study published October 3 in the journal Science.
[Related: Why is the sun’s corona 200 times hotter than its surface?]
What is the solar magnetic field?
The solar magnetic field is the primary driver of solar storms and flares. As society grows increasingly reliant on technology, this space weather poses threats to power grids, communication systems, and in-space technologies like GPS and satellites.
“We need to understand space weather. We need to predict space weather. The big gap in our knowledge is that we don’t have measurements of the magnetic field in the sun’s atmosphere, its corona,” says Gibson, who is a co-author of this new study. “That’s the part you see during a solar eclipse. The magnetic field controls the shape of that atmosphere, and it controls where the plasma, where the ‘stuff’ is.”
Measuring the magnetism of this region typically requires large, expensive equipment that has only been able to study small parts of the corona. However, a combination of coronal seismology and new observation methods now make it possible for researchers to produce consistent and comprehensive views of the magnetic field of the global corona.
“Global mapping of the coronal magnetic field has been a big missing part in the study of the Sun,” Zihao Yang, a study co-author from Peking University in China and a postdoctoral fellow at NCAR, said in a statement. “This research is helping us fill a crucial gap in our understanding of coronal magnetic fields, which are the source of the energy for storms that can impact Earth.”
A tale of two instruments
Scientists have been able to routinely measure the magnetic field on the sun’s surface called the photosphere. Measuring the much dimmer coronal magnetic field has been more difficult, limiting a deeper understanding of the three-dimensional structure and evolution of the magnetic field of the corona.
Large telescopes like the NSF’s Daniel K. Inouye Solar Telescope (DKIST) can measure the three-dimensional coronal magnetic fields in depth. With a huge aperture that measures 13-feet in diameter, DKIST is the world’s largest solar telescope. It recently demonstrated its ability for making detailed observations of the coronal magnetic field. However, DKIST can’t map the sun all at once.
[Related: See hot plasma bubble on the sun’s surface in powerful closeup images.]
To try to get more holistic mapping, the team turned to the Upgraded Coronal Multi-channel Polarimeter (UCoMP). UCoMP is better-suited to give scientists a more global picture of the coronal magnetic field, but in a lower resolution and in a two-dimensional projection.
Like an eclipse, UCoMP can block out parts of the sun. It uses a disc called a coronagraph to enable scientists to measure the sun’s atmosphere. UCoMP has a much smaller aperture compared to DKIST–about 7 inches–but it can take a wider view that makes it possible for scientists to study the entire sun on most days.
The team applied a method called coronal seismology to track magnetohydrodynamic (MHD) transverse waves in the UCoMP data. From the MHD waves, they could create a two-dimensional map of the strength and direction of the coronal magnetic field.
During the UCoMP study, the team produced 114 magnetic field maps between February and October 2022, about one almost every other day.
“We are entering a new era of solar physics research where we can routinely measure the coronal magnetic field,” said Yang.
Using DKIST’s and UCoMP’s measurements together offers a more holistic view of the coronal magnetic field.
Getting the picture
This research method also generated the first measurements of the coronal magnetic field in the sun’s polar regions. These poles have never been directly observed because the curve of the sun near the poles keeps it beyond our view from Earth.
While the team didn’t directly view the sun’s poles, they took measurements of the magnetism emitting from them for the first time. The improved data quality provided by UCoMP and the sun nearing its solar maximum helped them obtain this first of their kind measurements. The generally weak emissions from the polar region have been much stronger, which makes it easier to obtain coronal magnetic field results in the polar regions.
[Related: Rare quadruple solar flare event captured by NASA.]
The team will continue to research the magnetic fields, namely capturing the third dimension of the magnetic field. Getting a 3D view is particularly important for understanding how the corona is energized leading up to a solar eruption.
“It’s the first time we’ve ever seen the global coronal magnetic field, but it’s still kind of seeing like a 2D version of a 3D thing,” says Gibson.”
Eventually, the combination of a large telescope and a global field of view is needed to measure all of the three-dimensional twists behind solar eruptions. The proposed Coronal Solar Magnetism Observatory (COSMO), a solar refracting telescope almost five feet in diameter that is currently undergoing its final design study.
