With data from the Sun’s closest path to date, the ESA/NASA Solar Orbiter spacecraft has found compelling evidence about the origin of magnetic switches, and suggests how its physical formation mechanism could help accelerate the solar wind.
The Solar Orbiter has made the first remote sensing observations that correspond to a magnetic phenomenon called solar inversion – sudden and large deviations in the magnetic field of the solar wind. The new observation provides a complete view of the structure, and in this case confirms that it has an S-shaped character, as expected. Moreover, the global perspective provided by Solar Orbiter data suggests that these rapidly changing magnetic fields could have their origin near the surface of the Sun.
While a number of spacecraft have flown through these puzzling regions before, the in-situ data only allows measurements at one point and time. Thus, the switching structure and shape must be inferred from the plasma and magnetic field properties measured at one point.
When the German-American Helios 1 and 2 spacecraft flew close to the Sun in the mid-1970s, both probes recorded sudden reversals of the Sun’s magnetic field. These mysterious reversals have always been sudden and temporary, lasting from a few seconds to a number of hours before the magnetic field returns to its original direction.
These magnetic structures were also examined at much greater distances from the Sun by the Ulysses spacecraft in the late 1990s. Rather than the radius of Earth’s orbit from the Sun, where the Helios missions made their closest pass, Ulysses mostly worked outside of Earth’s orbit.
Their number skyrocketed with the arrival of NASA’s Parker Solar Probe in 2018. This clearly indicates that sudden magnetic field reversals are more numerous near the Sun, and led to the suggestion that they were caused by S-shaped kinks in the magnetic field. This baffling behavior has earned this phenomenon the name switch operations. A number of ideas have been proposed on how to form these.
On March 25, 2022, the Solar Orbiter was just a day away from a pass close to the sun – which put it in the orbit of the planet Mercury – and its Metis instrument was taking data. Metis blocks the bright glare of light from the sun’s surface and takes pictures of the sun’s outer atmosphere, known as the corona. Particles in the corona are electrically charged and follow the Sun’s magnetic field lines in space. The electrically charged particles themselves are called plasmas.
At approximately 20:39 UTC, Metis recorded an image of the solar corona that showed a distorted S-shaped distortion in the coronal plasma. For Daniele Teloni, National Institute of Astrophysics-Astrophysical Observatory in Turin, Italy, it looked suspiciously like a reflection of solar energy.
Comparing an image of Metis, taken in visible light, with a simultaneous image captured by the Solar Orbiter (EUI)’s Extreme Ultraviolet Imager (EUI) instrument, he saw that filter switching was occurring over an active region cataloged as AR 12972. Active regions are associated with sunspots and magnetic activity. Further analysis of Metis data showed that the velocity of the plasma over this region was very slow, as would be expected from an active region that had not yet released its stored energy.
Daniel immediately thought that this was similar to a generating mechanism for switching processes proposed by Professor Gary Zank, University of Alabama in Huntsville, USA. The theory looked at the way different magnetic regions near the surface of the Sun interact with each other.
Near the Sun, and especially above the active regions, there are open and closed magnetic field lines. The closed lines are magnetic rings that curve in the solar atmosphere before bending and disappearing again into the sun. Very little plasma can escape into space above these field lines, so the speed of the solar wind tends to be slow here. Open field lines are the opposite, they emanate from the Sun and connect to the solar system’s interplanetary magnetic field. They are magnetic highways along which plasma can flow freely, and they lead to fast solar winds.
Daniel and Gary demonstrated that switching processes occur when there is an interaction between the region of open field lines and the region of closed field lines. When field lines cluster together, they can reconnect in more stable configurations. Instead of breaking the whip, this releases energy and releases an S-shaped turbulence traveling into space, which a passing spacecraft will record as bouncing.
According to Gary Zank, who has proposed one of the theories about the origin of transpositions, “The first picture of Metis shown by Daniel almost immediately suggested to me the cartoon we drew in developing the mathematical model of regression. Of course, the first picture was just a snapshot, and we had to temper our enthusiasm. We even used Metis’ excellent coverage to extract temporal information and perform a more detailed spectroscopic analysis of the images themselves. The results proved to be absolutely stunning!”
Together with a team of other researchers, they built a computer model of the behavior, and found that their results bear a striking similarity to the Metis image, especially after they included calculations of how the structure elongated as it propagated outward through the solar corona. .
Daniel says, who The results are published in a paper In The Astrophysical Journal Letters.
In understanding switching processes, solar physicists may also take a step toward understanding the details of how the solar wind accelerates and heats away from the sun. This is because when spacecraft fly through the switch points, they often register a localized acceleration of the solar wind.
“The next step is to try to statistically correlate the shifts observed at the site with their source regions on the Sun,” Danielle says. In other words, to fly a spacecraft through the magnetic reversal and be able to see what happened on the surface of the Sun. This is exactly the kind of correlation science the Solar Orbiter is designed to do, but it doesn’t necessarily mean that the Solar Orbiter needs to fly through the switch. It could be another spacecraft, like the Parker Solar Probe. As long as the on-site and remote sensing data are in sync, Danielle can make the correlation.
“This is exactly the kind of result we were hoping for with the Solar Orbiter,” says Daniel Muller, ESA Solar Orbiter Project Scientist. “With each orbit, we get more data from our group of ten instruments. Based on results like these, we’ll fine-tune the planned observations of the Solar Orbiter’s upcoming solar encounter to understand how the Sun relates to the solar system’s broader magnetic environment. This was the first pass Solar Orbiter is very close to the Sun, so we expect more exciting results in the future.”
solar orbit The corridor near the sun – Once again inside Mercury’s orbit at a distance of 0.29 times the distance between the Earth and the Sun – it will take place on October 13. Earlier this month, on September 4, the Solar Orbiter made a gravitational-assisted flyby of Venus to adjust its orbit around the Sun; Subsequent Venus flybys will begin to raise the inclination of the spacecraft’s orbit to reach higher latitudes — more polar — than the Sun.
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