the original version of this story appeared in Quanta Magazine.
Our sun is the best observed star in the entire universe.
We see its light every day. For centuries, scientists have tracked the dark spots dotting its radiant face, while in recent decades, telescopes in space and on Earth have examined the sun’s rays at wavelengths spanning the entire electromagnetic spectrum. Experiments have also sniffed the Sun’s atmosphere, captured bursts of solar wind, collected solar neutrinos and high-energy particles, and mapped our star’s magnetic field (or attempted to, since we have yet to actually observe the regions polarities that are key to learning). about the internal magnetic structure of the sun.
However, despite all that scrutiny, a crucial question remained shamefully unresolved. On its surface, the sun is a warm 6,000 degrees Celsius. But the outer layers of its atmosphere, called the corona, can be a scorching (and disconcerting) 1 million degrees hotter.
You can see that scorching layer of gas during a total solar eclipse, as happened on April 8 above. a strip of North America. If you were in the path of totality, you could see the corona as a bright halo around the sun in the shadow of the moon.
This year, that halo looked different than the one that appeared during the last North American eclipse, in 2017. Not only is the Sun more active now, but you were looking at a structure that we, scientists who study our home star, have. . I finally came to understand. Observing the sun from afar did not allow us to understand what heats the corona. To solve this and other mysteries, we needed a space probe that would skim the sun.
That spaceship—the NASA one Parker solar probe—launched in 2018. As it orbits the sun, entering and exiting the solar corona, it has collected data that shows us how small-scale magnetic activity within the solar atmosphere causes the solar corona to become almost inconceivably hot .
From surface to cover
To begin to understand the toasted corona, we must consider magnetic fields.
The Sun’s magnetic motor, called a solar dynamo, is located about 200,000 kilometers below the Sun’s surface. As it rotates, that motor drives solar activity, which rises and falls over periods of approximately 11 years. When the sun is most active, solar flares, spots, and solar flares increase in intensity and frequency (as is happening now, near solar maximum).
On the sun’s surface, magnetic fields build up at the boundaries of churning convective cells, known as supergranules, that look like bubbles in a saucepan with boiling oil over heat. The constantly boiling solar surface concentrates and strengthens those magnetic fields at the edges of the cells. Those amplified fields then launch transient jets and nanoflares as they interact with the solar plasma.
Courtesy of NSO/NSF/AURA/Quanta Magazine
CAPTION: These churning convective cells on the sun’s surface, each about the size of the state of Texas, are closely related to the magnetic activity that heats the solar corona.
CREDIT: NSO/NSF/AURA
Magnetic fields can also pass through the surface of the sun and produce larger scale phenomena. In regions where the field is strong, dark sunspots and giant magnetic loops are seen. In most places, especially at the bottom of the solar corona and near sunspots, these magnetic arcs are “closed,” with both ends attached to the sun. These closed loops come in various sizes, from tiny to dramatic and burning bows seen during eclipses.