Unlike the Earth, the Sun does not have a solid surface. But around it is a region of space where it controls the crackling of its plasma; Beyond that, it cedes control. On April 28, 2021, NASA’s Parker Solar Probe crossed those limits, touching plasma and magnetic waves associated with the Sun.
This boundary is known as two thousand surface. Inside, the Sun’s magnetic field has a strong grip on the plasma, controlling its movements. The magnetic field outside this surface is weaker, and the plasma carries a charge, pulling magnetic field lines with it as it flows outward in the form of the solar wind.
The probe actually entered the magnetized atmosphere a total of three times during its eighth pass around the sun, explains Justin Kasper (University of Michigan, BWX Technologies, Inc.), principal investigator for the spacecraft’s particle-detector instruments. Casper led a study on the crossings published on December 14 in Physical Review LettersThe results were announced with other team members at the ongoing meeting of the American Geophysical Union.
Read more about the Parker Solar Probe mission in the November 2020 issue of Sky and telescopeAnd subscribe to support more stories like these.
How do you touch the sun?
The first time Parker crossed the surface of Alvin was the longest; He flew into the atmosphere for five hours. Even as it continued to fly toward the sun, it popped up again, sinking again with greater depth when it came in its closest approach—but for a brief time, it departed that time only half an hour later. Then, on its way out, the spacecraft vaulted again below the surface for a few hours.
“[The Alfvén surface] Casper says. “It’s not hazy – it’s well defined while we’re under it – but the surface has some structure.” So while the probe sees a smooth change in conditions while crossing the boundary, where Boundaries can change. The cause of this wrinkled surface remains an open question, although researchers suspect that crossing over a pseudotransmitter below the corona pushed the boundary outward to enable the first transit.
What is clear is that within the heliosphere, conditions are different from those outside. Parker saw the plasma waves moving back and forth instead of flowing outwards. This difference was visible not only to the SWEAP and FIELDS instruments, which measure particles and electric and magnetic fields, respectively, but also to the probe’s WISPR imager.
WISPR has revealed structures in the solar wind that scientists have never seen from their previous views. And not only did he photograph the structures, he actually flew across them. “Imagine you’re riding the Parker Solar Probe,” says Noor Al-Rawafi (Johns Hopkins Applied Physics Laboratory). “When you see the structures from afar, they look like they are in the same place in space. But if you are traveling through them, some of them may appear to fly over your head, while others pass under your feet.”
“We were flying through the source of the solar wind,” Al-Rawafi says.
The view inside the corona may shed light on the two main scientific objectives of the Parker Solar Probe: the origin of the solar wind and the heat source of the million-degree corona. Analysis to address these goals is ongoing and will soon include the 9th and 10th Parker Corridors. Preliminary analysis indicates that Passage IX also took Parker within the Alfvén surface; The data is still unrelated to the 10th pass, which occurred on November 21.
Sussing Out Switchbacks
From the perspective of the probe insiders, scientists may also find an explanation for Switch operations, “S” shape curves in the magnetic field. Although it has been known to exist since the 1990s, Parker has renewed interest in these structures because they have been ubiquitous in the solar wind.
“Is it forged on the surface of the sun? Or is it formed by some process that causes the field to breach on its way out of the sun?” asks Stuart Bell (University of California, Berkeley), principal investigator on the FIELDS instrument cluster.
While the answers to these questions are not yet known, the new observations show that switching processes occur in discrete spots, and tend to have a higher proportion of helium ions. that connects them to photosphere, the highest level of the Sun, where most of the photons we see come from.
“It just got more interesting,” Bell says. It indicates that the zigzag spots and their helium ions appear to be related magnetic funnel, Regions between giant convective cells in the sun’s boiling plasma. While it’s still too early to rule out any swap asset scenarios, he adds, “We’ll get there!”
Parker Solar Probe will continue to spiral toward the sun, with its next closest approach in February. As it approaches, solar activity also increases, promising additional insights into the future. ‘Humanity has touched the sun, and revolutionary discoveries are just beginning,’ says program scientist Kelly Couric (NASA HQ).
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