Parker Solar Probe flies into the fast solar wind and finds its source

NASA’s Parker Photo voltaic Probe (PSP) has flown shut sufficient to the sun to detect the fantastic construction of the solar wind near the place it’s generated on the sun’s floor, revealing particulars which might be misplaced because the wind exits the corona as a uniform blast of charged particles.

It is like seeing jets of water emanating from a showerhead via the blast of water hitting you within the face.

In a paper to be printed within the journal Nature, a staff of scientists led by Stuart D. Bale, a professor of physics on the College of California, Berkeley, and James Drake of the College of Maryland-Faculty Park, report that PSP has detected streams of high-energy particles that match the supergranulation flows inside coronal holes, which means that these are the areas the place the so-called “quick” solar wind originates.

Coronal holes are areas the place magnetic field strains emerge from the floor with out looping again inward, thus forming open area strains that broaden outward and fill most of space across the sun. These holes are normally on the poles through the sun’s quiet intervals, so the quick solar wind they generate does not hit Earth. However when the sun turns into energetic each 11 years as its magnetic area flips, these holes seem everywhere in the floor, producing bursts of solar wind aimed instantly at Earth.

Understanding how and the place the solar wind originates will assist predict solar storms that, whereas producing lovely auroras on Earth, also can wreak havoc with satellites and {the electrical} grid.

“Winds carry numerous info from the sun to Earth, so understanding the mechanism behind the sun’s wind is essential for sensible causes on Earth,” Drake stated. “That is going to have an effect on our capacity to know how the sun releases vitality and drives geomagnetic storms, that are a menace to our communication networks.”

Based mostly on the staff’s evaluation, the coronal holes are like showerheads, with roughly evenly spaced jets rising from brilliant spots the place magnetic field lines funnel into and out of the floor of the sun. The scientists argue that when oppositely directed magnetic fields cross each other in these funnels, which might be 18,000 miles throughout, the fields usually break and reconnect, slinging charged particles out of the sun.

“The photosphere is roofed by convection cells, like in a boiling pot of water, and the bigger scale convection circulate is named supergranulation,” Bale stated. “The place these supergranulation cells meet and go downward, they drag the magnetic area of their path into this downward sort of funnel. The magnetic area turns into very intensified there as a result of it is simply jammed. It is sort of a scoop of magnetic area taking place right into a drain. And the spatial separation of these little drains, these funnels, is what we’re seeing now with solar probe information.”

Based mostly on the presence of some extraordinarily high-energy particles that PSP has detected—particles touring 10 to 100 occasions sooner than the solar wind common—the researchers conclude that the wind may solely be made by this course of, which is named magnetic reconnection. The PSP was launched in 2018 primarily to resolve two conflicting explanations for the origin of the high-energy particles that comprise the solar wind: magnetic reconnection or acceleration by plasma or Alfvén waves.

“The large conclusion is that it is magnetic reconnection inside these funnel buildings that is offering the vitality supply of the quick solar wind,” Bale stated. “It does not simply come from all over the place in a coronal gap, it is substructured inside coronal holes to those supergranulation cells. It comes from these little bundles of magnetic vitality which might be related to the convection flows. Our outcomes, we predict, are robust proof that it is reconnection that is doing that.”

The funnel buildings probably correspond to the brilliant jetlets that may be seen from Earth inside coronal holes, as reported recently by Nour Raouafi, a co-author of the examine and the Parker Photo voltaic Probe undertaking scientist on the Utilized Physics Laboratory at Johns Hopkins College. APL designed, constructed, manages and operates the spacecraft.

Plunging into the sun

By the point the solar wind reaches Earth, 93 million miles from the sun, it has developed right into a homogeneous, turbulent circulate of roiling magnetic fields intertwined with charged particles that work together with Earth’s personal magnetic area and dump electrical vitality into the higher ambiance. This excites atoms, producing colourful auroras on the poles, however has results that trickle down into Earth’s ambiance. Predicting probably the most intense winds, referred to as solar storms, and their near-Earth penalties is one mission of NASA’s Dwelling With a Star program.

The probe was designed to find out what this turbulent wind seems to be like the place it is generated close to the sun’s floor, or photosphere, and the way the wind’s charged particles—protons, electrons and heavier ions, primarily helium nuclei—are accelerated to flee the sun’s gravity.

To do that, PSP needed to get nearer than 25 to 30 solar radii, that’s, nearer than about 13 million miles.

“When you get under that altitude, 25 or 30 solar radii or so, there’s so much much less evolution of the solar wind, and it is extra structured—you see extra of the imprints of what was on the sun,” Bale stated.

In 2021, PSP’s devices recorded magnetic area switchbacks within the Alfvén waves that appeared to be related to the areas the place the solar wind is generated. By the point the probe reached about 12 solar radii from the floor of the sun—5.2 million miles—the information had been clear that the probe was passing via jets of fabric, fairly than mere turbulence. Bale, Drake and their colleagues traced these jets again to the supergranulation cells within the photosphere, the place magnetic fields bunch up and funnel into the sun.

However had been the charged particles being accelerated in these funnels by magnetic reconnection, which might slingshot particles outward, or by waves of scorching plasma—ionized particles and magnetic area—streaming out of the sun, as in the event that they’re browsing a wave?

The truth that PSP detected extraordinarily high-energy particles in these jets—tens to a whole bunch of kiloelectron volts (keV), versus a couple of keV for many solar wind particles—informed Bale that it needs to be magnetic reconnection that accelerates the particles and generates the Alfvén waves, which probably give the particles an additional increase.

“Our interpretation is that these jets of reconnection outflow excite Alfvén waves as they propagate out,” Bale stated. “That is an commentary that is well-known from Earth’s magnetotail, as nicely, the place you’ve gotten comparable sort of processes. I do not perceive how wave damping can produce these scorching particles as much as a whole bunch of keV, whereas it comes naturally out of the reconnection course of. And we see it in our simulations, too. ”

The PSP will not be capable to get any nearer to the sun than about 8.8 solar radii above the floor—about 4 million miles—with out frying its devices. Bale expects to solidify the staff’s conclusions with information from that altitude, although the sun is now getting into solar most, when exercise turns into rather more chaotic and should obscure the processes the scientists are attempting to view.

“There was some consternation firstly of the solar probe mission that we will launch this factor proper into the quietest, most uninteresting a part of the solar cycle,” Bale stated. “However I feel with out that, we might by no means have understood this. It could have been simply too messy. I feel we’re fortunate that we launched it within the solar minimal.”