The Solar Orbiter spacecraft was travelling rapidly through space when a "hole" opened in the Sun's atmosphere near the south pole.

Actually, it wasn't a hole. It was a coronal hole. A spot in the Sun's outer atmosphere where the temperature drops. These "cold" spots are not as bright as the rest of the sun, which makes them appear black in images, like a deep hole.

When Solar Orbiter was monitoring the hole in March 2022, its powerful extreme ultraviolet instrument detected something no one had ever seen before: tiny flares exploding everywhere.

Look closely at the edge of the sun in the video image above. One of the small flares protrudes from the solar surface as a dark line.

Scientists have previously been unable to detect these mini-flares because they are so small - on the scale of the Sun. Each of these bright plasma jets is several hundred kilometres long and disappears after 20 to 100 seconds. Each one emits as much energy as 3,000 to 4,000 US households consume in a year, solar physicist Lakshmi Pradeep Chitta told Nature.

This is nothing compared to the solar flares scientists are used to. The largest type of solar flare is the class X flare, which emits energy equivalent to a billion hydrogen bombs. That's a billion times more energy than nano-flares at the other end of the spectrum.

The newly discovered explosions have 1,000 times less energy than a nano-explosion, which has one trillionth the energy of an X-explosion. That's why scientists have dubbed these findings "picoflars" in a new study published Thursday in the journal Science.

Because these picoflars are all over the coronal hole, researchers suspect that they are also present in the rest of the sun.

Picoflars could reveal one of the Sun's greatest secrets: How it produces a powerful current of electrically charged particles and strong magnetic fields, and how this current continually blasts the Earth.

This current, called the "solar wind", is overloaded when coronal holes or large solar flares are directed towards our planet. The resulting flooding can block radio signals on Earth, knock out power grids and even push satellites out of orbit. The consolation prize of such a solar storm is that it triggers beautiful auroras, the Northern Lights.

Scientists want to understand the solar wind to better predict it and give Earth more time to prepare for its effects.

Recent findings from NASA's Parker Solar Probe support the idea that previously unnoticed continuous flares may be fuelling the solar wind. These researchers have reported other "small-scale jet activity".

"Jets, in general, have been previously observed in the solar corona," Chitta, who leads the Solar Orbiter study and a team at the Max Planck Institute for Solar System Research, told Space.com. "The picoflare jets we observed are the smallest and energetically weakest jets that have not been previously observed in the solar corona."

Smaller, more frequent jets that we have not yet seen may also be fuelling the solar wind, the European Space Agency reported.

NASA and ESA launched Solar Orbiter in 2020 to study these winds at their source. Scientists hope to one day be able to better predict space weather from the sun.

Now is a great time to study this question, as the Sun's activity is heading towards the peak of its 11-year cycle. Solar flares, coronal holes and other powerful eruptions are becoming more common.

"In general, this is a gold mine right now," solar physicist Andrei Zhukov, who works with Solar Orbiter at the Royal Belgian Observatory in Brussels and is one of the authors of the new study, told the journal Nature.

 

Source: https://www.sciencealert.com/