Enlarge/ An artist’s depiction of the Parker Solar Probe, along with its subject.
The solar wind swarms with charged particles that can light up auroras, cause satellites to glitch, and damage electrical infrastructure on Earth. Despite its importance, we have a limited understanding of the forces that produce the wind, where it emerges from the Sun, and what accelerates it toward our planet.
Because the solar wind blasts outward with so much power, its immense strength has made it nearly impossible for spacecraft to see through the chaos and determine where it is generated—until now. NASA’s Parker Solar Probe was able to observe the Sun close enough to image the region where the solar wind originates. NASA scientists had previously predicted that it starts close to the surface and then gushes through “holes” in the Sun’s corona, the outer atmosphere, before being ejected into space. What Parker beamed back finally showed they were right.
A hole in the corona
“The fast solar wind that fills the heliosphere originates from deep within regions of open magnetic field on the Sun called ‘coronal holes,’” researchers from the Parker team said in a study recently published in Nature.
So what are “coronal holes”? These especially bright areas in the corona are open areas in the Sun’s magnetic field. Multiple magnetic field lines that reach all the way to the Sun’s surface pass through each hole, some heading toward the Sun, others away from it. When magnetic fields going in opposite directions collide, they break and then connect again in a phenomenon known as magnetic reconnection, spewing out plasma that flows along the field lines.
This is where the Parker discovery comes in. Parker was able to detect flows of the same highly energetic particles in the plasma that flows out of coronal holes. These particles are also found in what is known as the fast solar wind, which is almost twice as fast as slow solar wind, and they hit speeds of about 800 km per second (close to 500 miles/s). Parker’s extraordinary vision could also track the emergence of the solar wind from about 8 million km (13 million miles) away. At that distance, the solar wind has not quite morphed into a chaotic monster yet, so the probe could observe its much more structured beginnings closer to the surface. The fast solar wind particles it glimpsed were so energetic that they were also found to accelerate electromagnetic waves, known as Alfvén waves, which push its particles even further.
What powers the solar wind was debated for decades, as there was controversy over whether it was driven by magnetic reconnection or Alfvén waves. But until Parker’s advanced instruments could detect what was going on deeper within the Sun, there was no way to resolve the argument.
Seeking a connection
The Parker team created simulations of reconnection that matched the probe’s observations. “Reconnection directly heats the ambient coronal plasma sufficiently to drive the bulk outflow and at the same time produces the turbulent velocity bursts that ride this outflow,” the researchers said in their study.
While Parker tried to determine the origins of the solar wind before, it was in the wrong position, focused on a region of the Sun’s far side that was too distant to see what was going on in these “coronal holes.” There was also a chance it wouldn’t capture much activity because it was launched in 2018 during a solar minimum (the period with the least action). Solar maxima (the period with the most action) occurs every 11 years; the next solar maximum will be in 2025, but we haven’t had to wait for the maximum to catch some coronal holes.
Understanding where the solar wind originates should help us predict when it is headed our way and how quickly it will reach our planet. Knowing to plan ahead may enable us to protect satellites, electrical grids, and other sensitive equipment. This is especially important as we approach solar maximum when superfast gusts of solar wind are most likely to hit Earth.
Parker will be able to venture even closer to the Sun in the near future. Its instruments can take the heat up to 6.4 million km (4 million miles) away, twice as close as it approached this time. For now, it continues to stare at the Sun.
Nature, 2023. DOI: 10.1038/s41586-023-05955-3(About DOIs).
Elizabeth Rayne is a creature who writes. Her work has appeared on SYFY WIRE, Space.com, Live Science, Grunge, Den of Geek, and Forbidden Futures. When not writing, she is either shapeshifting, drawing, or cosplaying as a character nobody ever heard of. Follow her on Twitter @quothravenrayne.