For the primary time, a spacecraft has made contact with the solar. During a latest flyby, NASA’s Parker Solar Probe entered the solar’s environment.
“We have finally arrived,” Nicola Fox, director of NASA’s Heliophysics Science Division in Washington, D.C., stated December 14 in a information briefing on the fall assembly of the American Geophysical Union. “Humanity has touched the sun.”
Parker left interplanetary area and crossed into photo voltaic territory on April 28, 2021, throughout one in every of its shut encounters with the solar. While there, the probe took the primary measurements of precisely the place this boundary, referred to as the Alfvén essential floor, lies. It was about 13 million kilometers above the solar’s floor, physicists reported on the assembly, held on-line and in New Orleans, and in Physical Review Letters on December 14.
“We knew the Alfvén critical surface had to exist,” photo voltaic physicist Justin Kasper of the University of Michigan in Ann Arbor stated on the information briefing. “We just didn’t know where it was.”
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Finding this significant layer was one in every of Parker’s most important objectives when it launched in 2018 (SN: 7/5/18). The Alfvén essential floor is necessary as a result of it marks the place packets of plasma can separate from the solar and grow to be a part of the photo voltaic wind, the speedy stream of charged particles that continually emanates from the solar (SN: 8/18/17). The photo voltaic wind and different, extra dramatic types of area climate can wreak havoc on Earth’s satellites and even on life (SN: 2/26/21). Scientists need to pinpoint precisely how the wind will get began to higher perceive the way it can affect Earth.
The Alfvén essential floor additionally might maintain the important thing to one of many largest photo voltaic mysteries: why the solar’s corona, its wispy outer environment, is a lot hotter than the solar’s floor (SN: 8/20/17). With most warmth sources, temperatures drop as you progress farther away. But the solar’s corona sizzles at greater than one million levels Celsius, whereas the floor is only some thousand levels.
In 1942, physicist Hannes Alfvén proposed an answer to the thriller: A sort of magnetic wave would possibly carry vitality from the photo voltaic floor and warmth up the corona. It took till 2009 to straight observe such waves, within the decrease corona, however they didn’t carry sufficient vitality there to elucidate all the warmth (SN: 3/19/09). Solar physicists have suspected that what occurs as these waves climb larger and meet the Alfvén essential floor would possibly play a task in heating the corona. But till now, scientists didn’t know the place this frontier started.
With the boundary recognized, “we’ll now be able to witness directly how coronal heating happens,” Kasper stated.
As Parker crossed the invisible boundary, its devices recorded a marked improve within the power of the native magnetic subject and a drop within the density of charged materials. Out within the photo voltaic wind, waves of charged particles gush away from the solar. But under the Alfvén essential floor, a few of these waves bend again towards the floor of the solar.
Surprisingly, Parker’s measurements confirmed that the Alfvén essential floor is wrinkly. “That was one of the big outstanding questions,” says photo voltaic physicist Craig DeForest of the Southwest Research Institute in Boulder, Colo., who’s a member of the Parker probe staff however was not a part of this measurement.
“There was some debate in the community about whether the Alfvén surface would exist as a surface at all,” he says. Decades in the past, scientists imagined the boundary as a clean sphere surrounding the solar like a snow globe. More just lately, some thought it could be so ragged that it wouldn’t be obvious when the spacecraft crossed it.
Neither of these photographs turned out to be appropriate. The floor is clean sufficient that the second of crossing was noticeable, Kasper stated. But in the course of the spacecraft’s shut strategy to the solar in April, it crossed out and in of the boundary 3 times. The first dip lasted about 5 hours, the final solely half an hour.
“The surface clearly has some structure and warp to it,” Kasper stated.
That construction may affect every little thing from the best way photo voltaic eruptions go away the solar to the best way the photo voltaic wind interacts with itself farther out from the solar, DeForest says. “That has consequences that we don’t know yet, but are likely to be profound,” he says. “This is very exciting. It’s terra incognita.”
Parker remains to be orbiting the solar and planning to make a number of extra shut approaches over the following few years, finally getting inside 6 million kilometers of the photo voltaic floor. That ought to convey Parker into the photo voltaic corona repeatedly, photo voltaic physicist Nour Raouafi of the Johns Hopkins Applied Physics Laboratory in Laurel, Md., stated within the information briefing. The spacecraft might have made one other journey previous the Alfvén essential floor in August and may have one other alternative in January.
“The expectation is that as we fly closer and closer to the sun, we’ll keep crossing this boundary,” Raouafi stated. But the boundary won’t be in the identical place each time. As the solar’s exercise modifications, the extent of the Alfvén essential floor is predicted to rise and fall as if the corona is respiratory out and in, he stated.
That’s one other factor that scientists hope to look at for the primary time.