A spacecraft has made contact with the sun for the first time. NASA’s Parker Solar Probe has reached the sun’s atmosphere during a visit.
In a news briefing at the American Geophysical Union’s autumn conference on December 14, Nicola Fox, head of NASA’s Heliophysics Science Division in Washington, D.C., declared, “We have finally arrived.” The sun has been touched by humanity.
On April 28, 2021, Parker made one of its near encounters with the sun, leaving interplanetary space and entering solar territory. The probe made the initial measurements of the location of this barrier, also known as the Alfvén critical surface, while it was there. The meeting, which was held online and in New Orleans, as well as in Physical Review Letters on December 14 stated that it was around 13 million kilometers above the surface of the sun.
Solar physicist Justin Kasper of the University of Michigan in Ann Arbor stated at the press conference that “we knew the Alfvén critical surface had to exist.” We just were unaware of its location.
One of Parker’s primary objectives when it began in 2018 was to discover this essential layer. The Alfvén critical surface is significant because it indicates the location where plasma packets might break away from the sun and join the solar wind, the brisk stream of charged particles that continually flows from it.
Satellites from Earth as well as life itself are susceptible to damage from the solar wind and other, more severe types of space weather. In order to comprehend how the wind might affect Earth, scientists seek to determine precisely how it begins.
The reason why the sun’s corona, its thin outer atmosphere, is so much hotter than its surface may also be explained by the Alfvén critical surface (SN: 8/20/17). Temperatures tend to decrease the farthest you are from most heat sources. However, the surface of the sun barely reaches a few thousand degrees while its corona sizzles at over a million degrees.
A form of magnetic wave may convey energy from the solar surface and heat the corona, according to scientist Hannes Alfvén’s 1942 theory. Such waves were finally directly seen in the lower corona in 2009, but they didn’t convey enough energy to account for all the heat there (SN: 3/19/09).
It has been hypothesized by solar physicists that the heating of the corona may be caused by what occurs as those waves advance and collide with the Alfvén critical surface. But up until this point, scientists weren’t sure where this frontier started.
Now that the border has been located, “we’ll be able to directly observe how coronal heating occurs,” Kasper said.
The local magnetic field’s intensity significantly increased when Parker crossed the invisible border, and the quantity of charged particles significantly decreased. Waves of charged particles rush out from the sun and are carried away in the solar wind. Some of those waves, however, curve back toward the sun’s surface below the Alfvén critical surface.
Parker’s observations unexpectedly revealed that the Alfvén critical surface is wrinkled. Solar physicist Craig DeForest of the Southwest Research Institute in Boulder, Colorado, who is a member of the Parker probe team but was not involved in this measurement, said that “it was one of the great unresolved concerns.”
The existence of the Alfvén surface as a surface, he claims, was a topic of discussion among the community. The border was once thought of by scientists as a smooth sphere encircling the sun, similar to a snow globe. Until recently, some believed that it would be so ragged that the spacecraft wouldn’t be able to tell when it passed it.
Both of the pictures proved to be false. According to Kasper, the surface is sufficiently smooth that the crossing was apparent. However, the spacecraft entered and exited the barrier three times during its close approach to the sun in April. The last plunge lasted barely 30 minutes, while the previous one lasted almost five hours.
According to Kasper, “the surface certainly has some structure and warp to it.”
According to DeForest, that structure may have an impact on everything from the way solar eruptions exit the sun to how the solar wind interacts with itself further from the sun. “That has effects that we don’t yet understand, but they’re probably substantial,” he adds. This is really thrilling. It is uncharted territory.
In the next years, Parker, which is still in orbit around the sun, intends to make a number of more near encounters with the sun, eventually coming to within 6 million kilometers of its surface.
According to solar scientist Nour Raouafi of the Johns Hopkins Applied Physics Laboratory in Laurel, Maryland, this should repeatedly push Parker into the solar corona. Both in August and in January, the spacecraft will have another chance to pass the Alfvén critical surface.
It is anticipated that we will continue to breach this limit as we go closer to the sun, according to Raouafi. However, the border might not always be at the same location. He noted that the level of the Alfvén critical surface is anticipated to increase and decrease as the sun’s activity varies, like the corona breathing in and out.
Another thing that researchers want to see for the first time is that.