#coronal hole

— By Aristos Georgiou | August 24, 2023

Illustration of the ESA/NASA Solar Orbiter spacecraft observing the sun. The spacecraft has discovered numerous tiny jets of material escaping from the sun’s atmosphere that could be the source of the solar wind. ESA

Scientists have uncovered the mysterious source of a key solar phenomenon that has long-puzzled experts.

The Solar Orbiter spacecraft, developed by the European Space Agency (ESA) with contribution from NASA, discovered numerous tiny jets of material escaping from the sun's atmosphere.

Each of the tiny jets lasts between 20-100 seconds and expels plasma—a stage of matter consisting of superheated, charged particles—at a speed of around 224,000 miles per hour. The jets could be a long-sought-after source of the solar wind, according to a study published in the journal Science.

Our sun's outer atmosphere, or corona, constantly spews out a stream of plasma, known as the solar wind, that can reach speeds of more than 1 million miles per hour. This stream, which contains embedded solar magnetic field, expands throughout the entire solar system reaching far beyond the orbit of Pluto before it meets the interstellar medium.

The solar wind and magnetic field inflate a vast "bubble" in the surrounding interstellar material, which is known as the heliosphere.

Variations in the solar wind can produce several space weather phenomena that affect Earth. For example, under certain circumstances, it can interact with the Earth's magnetic field in a way that produces auroras.

Meanwhile, particularly high-speed streams of solar wind can result in geomagnetic storms that have the potential to disrupt navigation systems and produce harmful currents in power grids and pipelines, among other impacts.

"Understanding the solar wind is a key prerequisite for understanding space weather. Results like these are steps towards understanding the dynamic nature of the solar wind," ESA solar physicist Daniel Müller told Newsweek.

The solar wind is a fundamental feature of the sun but understanding exactly how and where it is generated has proven elusive, even though scientists have been studying the question for decades.

But the advanced instrumentation on the Solar Orbiter, considered the most complex scientific laboratory ever sent to study our star, has now shed new light on what drives the generation of the solar wind.

For the latest study, scientists examined data collected by the Solar Orbiter's Extreme Ultraviolet Imager (EUI) instrument.

In March 2022, this instrument took images of the sun's south pole, which researchers then analyzed. This revealed numerous short-lived and tiny jets, each one expelling plasma into space.

"We could only detect these tiny jets because of the unprecedented high-resolution, high-cadence images produced by EUI," Lakshmi Pradeep Chitta with the Max Planck Institute for Solar System Research, Germany, and the principal author on the paper, said in a press release.

The tiny jets that the researchers observed could be seen emanating from a structure on the sun known as a coronal hole. These vast holes are regions where the sun's magnetic field does not turn back down into the star. Instead, the magnetic field stretches out deep into the solar system.

It's been known for decades that some of the solar wind that the sun produces is generated in these regions. (Coronal holes which are most prevalent and stable at the sun's north and south poles, produce solar wind of relatively high speed. The solar wind that emanates from the equatorial regions of the sun, where there are fewer coronal holes, on the other hand, tends to be slower in speed).

But while scientists knew that high-speed solar wind originated from coronal holes, how exactly the plasma was launched remained something of a mystery. Now, the latest findings suggest that the tiny jets may be responsible for launching the plasma that feeds the solar wind as they travel away from the sun.

The study also challenges previous assumptions that the high-speed solar wind from coronal holes emerges in flows that are relatively steady. The researchers found that to a large extent, this flow is not actually uniform but is instead highly intermittent.

"This paper shows that also the fast solar wind is much more dynamic than originally thought," Müller told Newsweek.

The jets that the team discovered produce relatively little energy in the grand scheme of solar activity. For context, the most powerful corona phenomena, known as X-class solar flares, produce around a billion times more energy than so-called nanoflares. But the tiny jets are even a thousand times less energetic than these nanoflares.

Images from the ESA/NASA Solar Orbiter spacecraft show tiny jets of material escaping from the sun’s outer atmosphere. The jets show up as dark streaks across the solar surface in this mosaic. EUI TEAM/SOLAR ORBITER/ESA & NASA

The fact that the scientists saw so many of the tiny jets in the recent observations indicates that they are expelling a substantial fraction of the material that can be found in the solar wind.

"I think it's a significant step to find something on the disc that certainly is contributing to the solar wind," David Berghmans, principal investigator for the EUI instrument with the Royal Observatory of Belgium, said in the press release.

But it is possible that there could be other even smaller and more frequent events that could be contributing further.

Future research will be able to shed light on this issue. Currently, the Solar Orbiter is circling the sun close to the star's equator. This means that the tiny jets at the South Pole could only be seen edge-on, making it harder to measure some of their properties.

But as the Solar Orbiter mission continues, it will gradually incline its orbit toward the uncharted polar regions

"In a few years, we will see them from a different perspective than any other telescopes or observatories so that together should help a lot," Müller said in the press release.

The latest findings, alongside other observations being made by the Solar Orbiter, have implications for our understanding of space weather, according to Müller.

Aurora on Ice by Stephane Vetter  ( Nuits sacrées )

A Hole in the Sun's Atmosphere: The 1st Solar Views from New Satellite

A sun imager aboard the GOES-16 satellite captured its first, vivid images, showing a "hole" in the sun's hot upper atmosphere, called the corona.

The sun is reaching a minimum in its 11-year-cycle of activity. As a result, solar flares and the associated coronal mass ejections, which send charged particles into space that sometime collide with Earth, are also at a minimum right now.

This means that coronal holes are the primary space weather phenomena, NASA officials said. The one imaged by the National Oceanic and Atmospheric Administration's satellite on Jan. 29 caused auroras to appear on Earth.

Read more/video (with some good background music) ~ Space.com