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() — A solar mission that has been spiraling closer to the Sun to unlock some of its secrets flew close enough to the surface of our star to make a key discovery.
Data from the Parker Solar Probe revealed the origin of the solar wind, a stream of energized particles flowing from the corona — the Sun’s outer atmosphere — toward Earth.
One of the objectives of the mission, named after the deceased astrophysicist Eugene Parker and launched in 2018, was to determine what the wind looks like when it forms near the Sun and how it escapes the star’s gravity.
As the probe approached about 20.9 million kilometers from the Sun, its instruments detected fine structures in the solar wind where it is generated, near the photosphere—or the solar surface—and captured fleeting details that disappear once the wind is gone. expelled from the crown.
The spacecraft was specially designed to eventually fly 4 million miles above the solar surface and, in late 2021, became the first mission to “touch” the Sun.
A study detailing the solar findings was published Wednesday in the Nature magazine.
Untangling the solar wind
The solar wind is a continuous flow of plasma containing charged particles such as protons and electrons. The long-range phenomenon also includes part of the solar magnetic field and extends well beyond the corona, interacting with planets and the interstellar medium.
There are two types of this wind. The fastest solar wind flows from coronal holes at the Sun’s poles at a top speed of 800 kilometers per second. The slowest solar wind, located in the same plane of the solar system as Earth, flows at a speed of 400 kilometers per second.
The fast solar wind does not usually impact the Earth. But during the solar cycle maximum, an 11-year period during which the Sun’s activity gradually increases, the Sun’s magnetic field reverses. This spin causes coronal holes to appear on the Sun’s surface and release gusts of solar wind directly toward Earth.
Illustration shows Parker Solar Probe approaching the Sun. (JHU Laboratory of Applied Physics/NASA Goddard Space Flight Center)
Understanding the source of the solar wind can help scientists better predict space weather and solar storms that can affect Earth.
Solar storms cause beautiful auroras, but they can also affect Earth’s satellites and power grids.
“Winds carry a lot of information from the Sun to Earth, so understanding the mechanism behind the Sun’s wind is important for practical reasons on Earth,” said study co-author James Drake, a professor of physics at the University of Maryland, College Park, in a statement. “That will affect our ability to understand how the Sun releases energy and generates geomagnetic storms, which are a threat to our communication networks.”
The spacecraft data revealed that coronal holes act like shower heads, where jets appear on the Sun’s surface as bright spots, marking where the photosphere’s magnetic field enters and exits.
As the magnetic fields intersect, moving in opposite directions inside these funnels on the solar surface, they break and reconnect, sending charged particles flying out of the Sun.
“The photosphere is covered by convective cells, like in a boiling pot of water, and the larger-scale flow of convection is called supergranulation,” said the study’s lead author, Stuart D. Bale, a professor of physics at the University of California, Berkeley, in a statement.
“Where these supergranulation cells meet and descend, they drag the magnetic field on their way to this type of descending funnel. The magnetic field gets really strong there because it’s just stuck. It’s kind of like a ball of magnetic field going down a drain. And the spatial separation of those little drains, those funnels, is what we’re seeing now with the solar probe data.”
The Parker Solar Probe detected highly energetic particles traveling 10 to 100 times faster than the solar wind, leading the researchers to believe that the fast solar wind is created by reconnecting magnetic fields.
“The big takeaway is that it is the magnetic reconnection within these funnel structures that provides the power source for the fast solar wind,” Bale said. “Not only does it come from everywhere in a coronal foramen, it is substructured within the coronal foramen of these supergranulation cells. It comes from these little packets of magnetic energy that are associated with convection flows. We believe our results are strong evidence that it is the reconnection that is doing that.”
the sun cycle
The Sun is expected to reach solar maximum in July 2025, so there have been increasing reports of solar flares and northern and southern lights visible in unexpected places. Fortunately, the Parker Solar Probe and a separate mission—Solar Orbiter—are perfectly poised to observe the powerful and dynamic forces of the Sun at play.
But scientists are thankful that the Parker Solar Probe launched before the Sun rose dramatically during the calmer solar minimum, when chaotic activity had no chance of impairing observations.
“There was some consternation at the start of the solar probe mission because we thought we were going to launch this right into the quieter, duller part of the solar cycle,” Bale said. “But I think without that, we never would have understood this. It would have been too messy. I think we’re lucky we launched it at solar minimum.”
