Scientists are getting closer to understanding the sun’s ‘campfire’ flares

DALLAS — Scientists are starting to figure out what causes tiny eruptions on the sun called campfire flares.

Campfires were discovered in 2020, when the European Space Agency’s Solar Orbiter probe snapped closeup photos of our parent star and spotted diminutive flickers of ultraviolet light (SN: 7/16/20). The flashes resemble more massive explosions such as solar flares and coronal mass ejections but are only a millionth or a billionth the size.

Using observations of 52 campfires, solar physicist Navdeep Panesar and her colleagues tracked these bursts from their beginnings. The team noticed that nearly 80 percent of the campfires were preceded by a dark structure made from cool plasma, Panesar reported April 9 at the Triennial Earth-Sun Summit.

“When this cool plasma rises, a brightening appears underneath it. That brightening turns into a campfire,” says Panesar, of Lockheed Martin Solar and Astrophysics Laboratory in Palo Alto, Calif.

Such cool plasma structures also precede coronal jets, another of the sun’s recurring explosions. The findings suggest these plasma structures are more common than previously believed, Panesar says, and that many solar eruptions — campfires, jets, flares and mass ejections — arise in a similar fashion.

Flares and mass ejections occur when magnetic fields of opposite polarities get tangled and cancel one another out, leading to a powerful release of energy. Campfires are believed to be produced via similar mechanisms, though a full understanding has so far eluded researchers.

Since campfires tend to be between half a million and 2.5 million degrees Celsius, they are thought to help heat the sun’s million-degree atmosphere, the corona. Understanding why the corona is so much hotter than the sun’s surface, which is a mere 5500° C, has been a longstanding problem for solar physicists (SN: 2/27/20).