2023-06-08 09:00:02
Although it is our most everyday star, the Sun still keeps many secrets. For example, it is not known for sure why the Sun’s atmosphere (called the corona) is so much hotter than its surface; or how their mysterious 11-year cycles work. The mechanism that drives the solar wind is also unknown, of which there are two types: a ‘slow’ one, which only travels at 400 kilometers per second; and another much faster, which doubles that speed. Until now, all theories could predict speeds of 200 or 300 k/s, but never such high speeds. A new study using data collected by NASA’s Solar Parker Probe has found the source of this elusive phenomenon. The results have just been published in the journal ‘Nature‘.
The spacecraft is the fastest ever built by mankind and the one that will come closest to the Sun. However, it has already flown close enough to detect the fine structure of the solar wind near where it is generated on the surface of our star, revealing details that are lost when the wind blows out of the corona in a uniform explosion of charged particles. According to the study authors, “it’s like watching the jets emanate from the shower head while the water hits you in the face.”
A team led by Stuart D. Bale, professor of physics at the University of California, Berkeley, and James Drake of the University of Maryland-College Park, reports that the Parker Solar Probe has detected streams of high-energy particles that match the supergranulation flowing inside the coronal holes, suggesting that these are the regions where the so-called “fast” solar wind (the one that travels at 800 kilometers/second) originates.
changing coronal foramina
Coronal holes are areas where the Sun’s magnetic field lines emerge from the surface without receding inward, thus forming open field lines that expand outward. These holes are usually at the poles during our star’s quiet periods, so the fast solar wind they generate doesn’t hit Earth. But when the Sun becomes active every 11 years (the next peak of activity will be between late next year and early 2025) as its magnetic field changes, these holes appear all over the surface, generating gusts of solar wind. directed directly at us.
Understanding how and where the solar wind originates will help predict solar storms, which, while usually just the cause of the beautiful northern lights, in their most violent expressions can affect communications, satellites, and even power grids on Earth. Land. they can wreak havoc on satellites and the power grid.
“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,” says Drake. “That will affect our ability to understand how the sun releases energy and generates geomagnetic storms, which are a threat to our communication networks.”
Like a clogged shower head
According to the team’s analysis, coronal holes are like shower heads, with roughly evenly spaced jets emerging from bright spots where magnetic field lines enter and exit the Sun’s surface. The scientists argue that when magnetic fields Oppositely directed intersect in these funnels, which can be about 30,000 kilometers wide, the fields often break and reconnect, spewing charged particles into space.
“The photosphere is covered by convection cells, like in a boiling pot of water, and the larger-scale flow of convection is called supergranulation,” Bale explains. ‘Where these supergranulation cells meet and descend, they drag the magnetic field on their way into this 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.”
Based on the presence of some extremely high-energy particles that the NASA spacecraft has detected, the researchers conclude that wind could only be generated by this process, which is called magnetic reconnection. The Parker Solar Probe was launched in 2018 primarily to resolve two conflicting explanations for the origin of the high-energy particles that make up the solar wind: magnetic reconnection or acceleration by plasma or Alfvén waves.
“The big takeaway is that it is the magnetic reconnection within these funnel structures that provides the power source for the fast solar wind,” says Bale. “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.”
To reach these conclusions, the probe had to get close to 20 million kilometers. “Once you’re below that altitude, there’s much less solar wind evolution and it’s more structured: you see more traces than there was on the Sun,” says Bale, whose team traced these jets back to supergranulation cells in the Sun. photosphere, where magnetic fields are bundled together and channeled toward the Sun.
However, the probe will not be able to get closer to our star more than about 6 million kilometers without frying its instruments. Bale hopes to solidify the team’s conclusions with data from that altitude, even though the sun is now entering solar maximum, when the activity becomes much more chaotic and can obscure the processes scientists are trying to see.
“There was some consternation at the start of the solar probe mission that we were going to launch this right at the quietest, most boring part of the solar cycle,” Bale says. “But I think without that, we never would have understood this. It would have been too complicated. I think we’re lucky we launched it at solar minimum.”
#NASA #spacecraft #close #star #finds #source #enigmatic #solar #wind