Researchers could observe the middle corona of the sun in a world first

Thanks to a novel technique, scientists are now a step closer to solving a key mystery about the origins of solar wind.
Sade Agard
Newly discovered solar web
Newly discovered solar web

Courtesy of SwRI/NOAA 

Researchers have discovered web-like plasma structures in the Sun's middle corona, according to a recent study published in Nature Astronomy.

The results bring us closer to solving a fundamental mystery about solar wind's origins and its connections with other solar system bodies. 

A gap from the 90s finally bridged 

Researchers from the Southwest Research Institute (SwRI), NASA, and Max Planck Institute for Solar System Research (MPS) detailed their ground-breaking new observation technique in the study, which involves taking ultraviolet (U.V.) images of the middle corona. 

While the U.S. National Oceanic and Atmospheric Administration have been observing the Sun's corona since 1995 to track space weather, this has been carried out with subpar instruments. That is, the Large Angle and Spectrometric Coronagraph (LASCO) mounted on the NASA and European Space Agency Solar and Heliospheric Observatory (SOHO) spacecraft. 

As a result, LASCO has an observational gap that prevents us from seeing the middle solar corona, where the solar wind is generated.

"We've known since the 1950s about the outflow of the solar wind. As the solar wind evolves, it can drive space weather and affect things like power grids, satellites, and astronauts," said SwRI Principal Scientist Dr. Dan Seaton in a press release- one of the study's authors. 

"We haven't had observations like these before"

"The origins of the solar wind itself and its structure remain somewhat mysterious. While we have a basic understanding of processes, we haven't had observations like these before, so we had to work with a gap in information," he added.

Seaton proposed pointing a different instrument to identify new techniques to observe the Sun's corona (GOES). This would be the Solar Ultraviolet Imager (SUVI) on NOAA's Geostationary Operational Environmental Satellites (GOES). 

However, SUVI would be pointed at either side of the Sun rather than directly at it. Additionally, U.V. observations would be taken for a month. 

Solar wind originates from this 'web'

Researchers could observe the middle corona of the sun in a world first
Solar flare taken by Hinode's Solar Optical Telescope back in 2007

Seaton and his colleagues discovered elongated, web-like plasma structures in the Sun's middle corona. Significantly, they suggest that solar wind, in the form of particles, is propelled into space by interactions within these structures, which release stored magnetic energy.

"No one had monitored what the Sun's corona was doing in U.V. at this height for that amount of time. We had no idea if it would work or what we would see," he said. 

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"The results were very exciting. For the first time, we have high-quality observations that completely unite our observations of the Sun and the heliosphere as a single system."

According to the news release, Seaton thinks the novel observation method could lead to deeper understandings and even more thrilling mission discoveries. 

New depth for a mission set to launch in 2023

Future missions could include PUNCH (Polarimeter to Unify the Corona and Heliosphere), a NASA mission conducted by SwRI that will photograph the process by which the solar wind is formed from the Sun's outer corona. This is due to launch next year (2023). 

"Now that we can image the Sun's middle corona, we can connect what PUNCH sees back to its origins and have a more complete view of how the solar wind interacts with the rest of the solar system," he explained. 

"Prior to these observations, very few people believed you could observe the middle corona to these distances in U.V. These studies have opened up a whole new approach to observing the corona on a large scale," Seaton concluded. 

What is the Sun's corona?

Just in case you've arrived at this point with little understanding of what the Sun's corona actually is, here's a quick summary. The outermost region of the Sun's atmosphere is known as the corona. The Sun's intense surface light typically obscures the corona. Without employing specific tools, it becomes challenging to see. The corona can, nevertheless, be seen during a total solar eclipse.

The middle corona, about 650,000 miles (1 million kilometers) above the Sun's surface, is the area of the solar atmosphere that has received the least attention. This is partly because there have been no observations of the Sun's corona for altitudes lower than 1.3 million miles (2 million kilometers).

Abstract:

The solar wind consists of continuous streams of charged particles that escape into the heliosphere from the Sun, and is split into fast and slow components, with the fast wind emerging from the interiors of coronal holes. Near the ecliptic plane, the fast wind from low-latitude coronal holes is interspersed with a highly structured slow solar wind, the source regions and drivers of which are poorly understood. Here we report extreme-ultraviolet observations that reveal a spatially complex web of magnetized plasma structures that persistently interact and reconnect in the middle corona. Coronagraphic white-light images show concurrent emergence of slow wind streams over these coronal web structures. With advanced global magnetohydrodynamics coronal models, we demonstrate that the observed coronal web is a direct imprint of the magnetic separatrix web (S-web). By revealing a highly dynamic portion of the S-web, our observations open a window into important middle-coronal processes that appear to play a key role in driving the structured slow solar wind.