The unique model of this story appeared in Quanta Journal.
Our solar is the best-observed star in your complete universe.
We see its mild day by day. For hundreds of years, scientists have tracked the darkish spots dappling its radiant face, whereas in current many years, telescopes in house and on Earth have scrutinized sunbeams in wavelengths spanning the electromagnetic spectrum. Experiments have additionally sniffed the solar’s ambiance, captured puffs of the photo voltaic wind, collected photo voltaic neutrinos and high-energy particles, and mapped our star’s magnetic discipline—or tried to, since now we have but to essentially observe the polar areas which are key to studying concerning the solar’s inside magnetic construction.
For all that scrutiny, nevertheless, one essential query remained embarrassingly unsolved. At its floor, the solar is a toasty 6,000 levels Celsius. However the outer layers of its ambiance, referred to as the corona, generally is a blistering—and perplexing—1 million levels hotter.
You’ll be able to see that searing sheath of fuel throughout a complete photo voltaic eclipse, as occurred on April 8 above a swath of North America. Should you have been within the path of totality, you possibly can see the corona as a glowing halo across the moon-shadowed solar.
This yr, that halo regarded completely different than the one which appeared over the last North American eclipse, in 2017. Not solely is the solar extra energetic now, however you have been taking a look at a construction that we—the scientists who examine our house star—have lastly come to grasp. Observing the solar from afar wasn’t adequate for us to understand what heats the corona. To resolve this and different mysteries, we would have liked a sun-grazing house probe.
That spacecraft—NASA’s Parker Photo voltaic Probe—launched in 2018. Because it loops across the solar, dipping out and in of the photo voltaic corona, it has collected knowledge that reveals us how small-scale magnetic exercise inside the photo voltaic ambiance makes the photo voltaic corona virtually inconceivably scorching.
From Floor to Sheath
To start to grasp that roasting corona, we have to take into account magnetic fields.
The solar’s magnetic engine, referred to as the photo voltaic dynamo, lies about 200,000 kilometers beneath the solar’s floor. Because it churns, that engine drives photo voltaic exercise, which waxes and wanes over durations of roughly 11 years. When the solar is extra energetic, photo voltaic flares, sunspots, and outbursts enhance in depth and frequency (as is occurring now, close to photo voltaic most).
On the solar’s floor, magnetic fields accumulate on the boundaries of churning convective cells, often known as supergranules, which seem like bubbles in a pan of boiling oil on the range. The continuously boiling photo voltaic floor concentrates and strengthens these magnetic fields on the cells’ edges. These amplified fields then launch transient jets and nanoflares as they work together with photo voltaic plasma.
Courtesy of NSO/NSF/AURA/Quanta Journal
CAPTION: These churning convective cells on the solar’s floor, every roughly the dimensions of the state of Texas, are intently linked to the magnetic exercise that heats the solar’s corona.
CREDIT: NSO/NSF/AURA
Magnetic fields also can erupt by the solar’s floor and produce larger-scale phenomena. In areas the place the sector is robust, you see darkish sunspots and large magnetic loops. In most locations, particularly within the decrease photo voltaic corona and close to sunspots, these magnetic arcs are “closed,” with each ends hooked up to the solar. These closed loops are available in numerous sizes—from minuscule ones to the dramatic, blazing arcs seen throughout eclipses.
