Sun 'smoke rings' give clue to solar wind mystery

What has the sun been smoking? The most complete photographs yet taken of the sun’s atmosphere show patterns that resemble smoke rings. These may help astronomers unravel what drives the solar wind, the stream of charged particles that flows from the sun and permeates the solar system.

The patterns, some of which also resemble expanding bubbles and mushrooms, arise in the sun’s outer atmosphere, or corona, where the solar wind is thought to emanate from. Although similar formations were spotted there before, their cause had eluded astronomers.

Now, using a high-resolution eclipse-imaging technique, a team led by Miloslav Druckmüller at the Brno University of Technology in the Czech Republic has linked the strange patterns to plasma eruptions on the sun’s surface, called solar prominences.

The team came to this conclusion by superimposing about 60 separate photographs of solar eclipses, during which the corona is visible as a white halo around the blacked-out sun. The resulting composite images provided a new view of the sun that spanned all the way from the surface to far out in the corona: by contrast, previous images of such high resolution have typically been confined to one region or another.

The researchers were able to link particular patterns to particular prominences, and concluded that prominences are the likely cause of the patterns. Below you can see a prominence close to the sun’s surface and a “smoke ring” marked by the arrow.

(Image: Miloslav Druckmüller)

Because they are much smaller than other solar eruptions – like flares or coronal mass ejections – prominences had previously been thought to have a relatively minor effect on the sun’s atmosphere, and therefore also on the solar wind.

The new hi-res composite images change that, suggesting instead that prominences could be one of the driving forces for the solar wind, since to create the smoke rings, and other patterns in the corona, they must be creating much larger atmospheric disturbances than previously thought, with a much longer range.

“Our findings are the first to suggest that prominences are sources of significant wave generation in the inner corona, and could therefore contribute to the acceleration of solar wind particles,” says team member Shadia Habbal.

Space protection

“This strengthens the theory that prominences are one of the drivers of the solar wind,” agrees Nicolas Labrosse at the University of Glasgow, UK, who was not involved with the study.

The solar wind helps create auroras in Earth’s atmosphere, the tails of comets and the protective bubble encapsulating the solar system called the heliosphere. It can also interfere with spacecraft by giving rise to electromagnetic disturbances around Earth known as space weather. But despite all this, the mechanism behind the solar wind remains something of a mystery.

“These observations will hopefully help us better understand the life cycle of solar prominences and their connection with the rest of the heliosphere, ultimately providing a better insight into how to protect ourselves against damaging space weather,” Labrosse says.

Journal reference: The Astrophysical Journal, doi.org/shx