NASA's Parker Solar Probe flies close to the sun, spots origin of 'fast' solar winds

These holes emit high-speed particles from the sun like water from a shower head. 
Mrigakshi Dixit
Artist’s concept of the Parker Solar Probe spacecraft approaching the sun.
Artist’s concept of the Parker Solar Probe spacecraft approaching the sun.


NASA's Parker Solar Probe made a key discovery that unveiled the source of fast solar winds.

In December 2021, the probe 'touched the Sun', measuring particles and magnetic fields as it flew through the star's upper atmosphere. The probe was launched in 2018 to study the heating of the solar corona, and to investigate what accelerated solar wind.

Solar winds are a stream of highly charged particles that are emitted from the sun's outer atmosphere(corona) and spreads across the solar system. Fast solar winds have been a mystery for decades.

Until now.

In a paper published this week, a team of scientists from the University of California, Berkeley, and University of Maryland-College Park, reported on the intriguing source of these powerful solar winds, a press release stated.

The source of fast solar winds

The Parker Solar probe observed narrow plasma structures as it got close to around eight million kilometers of the sun's surface. These streams appear to be controlled by magnetic fields that trace back to the sun's cold spots known as coronal holes.

Coronal holes are the vast spots on the sun's surface where magnetic field lines do not circle back inside, but instead, produce open field lines that rush out into space.

Simply put, these holes emit high-speed particles from the sun like water from a shower head. 

These particle jets appear as temporary bright spots on the sun's surface and highlight where the magnetic field passes in and out of the photosphere (the sun’s visible surface). 

According to the release, as magnetic fields pass each other in opposing directions within these solar surface funnels, they break and reconnect, thereby sending charged particles hurtling out of the sun.

“The big conclusion is that its magnetic reconnection within these funnel structures that are providing the energy source of the fast solar wind,” Stuart D. Bale, a professor of physics at the University of California, Berkeley, said in a statement.

Bale added: “It doesn’t just come from everywhere in a coronal hole, it’s substructured within coronal holes to these supergranulation cells. It comes from these little bundles of magnetic energy that are associated with convection flows. Our results, we think, are strong evidence that it’s reconnection that’s doing that.”

Which means, the probe observed highly energetic particles traveling at a speed about 10 to 100 times faster than the solar wind, implying that the fast wind is caused by magnetic field reconnection blasted out from these holes.

NASA's Parker Solar Probe flies close to the sun, spots origin of 'fast' solar winds
The two dark regions below the middle of the image are the coronal holes sampled by the Parker Solar Probe.

Why is it essential to study solar winds?

Understanding how and where solar wind originates is critical for forecasting solar storms and space weather. These solar storms, composed of charged particles, mingle with the Earth's atmosphere to produce spectacular auroras. However, strong storms may cause satellites and the electrical system to fail.

“Winds carry lots of information from the sun to Earth, so understanding the mechanism behind the sun’s wind is important for practical reasons on Earth,” said James Drake of the University of Maryland-College Park. Drake added: “That’s going to affect our ability to understand how the sun releases energy and drives geomagnetic storms, which are a threat to our communication networks.”

With this discovery, scientists are one step closer to better understanding the complex dynamics of our star's turbulent surface. 

The results have been published in the journal Nature.

Study Abstract:

The fast solar wind that fills the heliosphere originates from deep within regions of open magnetic field on the Sun called ‘coronal holes’. The energy source responsible for accelerating the plasma is widely debated; however, there is evidence that it is ultimately magnetic in nature, with candidate mechanisms including wave heating and interchange reconnection. The coronal magnetic field near the solar surface is structured on scales associated with ‘supergranulation’ convection cells, whereby descending flows create intense fields. The energy density in these ‘network’ magnetic field bundles is a candidate energy source for the wind. Here we report measurements of fast solar wind streams from the Parker Solar Probe (PSP) spacecraft that provide strong evidence for the interchange reconnection mechanism. We show that the supergranulation structure at the coronal base remains imprinted in the near-Sun solar wind, resulting in asymmetric patches of magnetic ‘switchbacks’ and bursty wind streams with power-law-like energetic ion spectra to beyond 100 keV. Computer simulations of interchange reconnection support key features of the observations, including the ion spectra. Important characteristics of interchange reconnection in the low corona are inferred from the data, including that the reconnection is collisionless and that the energy release rate is sufficient to power the fast wind. In this scenario, magnetic reconnection is continuous and the wind is driven by both the resulting plasma pressure and the radial Alfvénic flow bursts.

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