The spacecraft used Venus flybys to sling itself successively closer to the sun, and on April 28, 2021, it touched the corona for the first time. It was now the closest spacecraft to our star and the fastest human-made object ever launched. (In fact, last month it passed by the sun for the 18th time at a speed that would get you from Washington, D.C., to Los Angeles in about 20 seconds, and from the Earth to the moon in 36 minutes.)
From near Earth, the solar wind looks like a turbulent fluid that is loosely related to the sun at only the largest scales. But from up close, its structure directly reflects the structures on the solar surface. Instead of being a disorganized fluid, the near-sun solar plasma whooshes outward in streamlets that often match the sizes of the convective supergranules on the sun’s surface — the cells around which magnetic fields concentrate, amplify and escape into the corona.
During each solar orbit, the spacecraft zoomed through those streamlets, and it found a telltale fingerprint of magnetic activity that permeated the plasma and pointed to a source for the corona’s heat. Called “switchbacks,” these fingerprints were S-shaped structures formed by brief reversals in the locally measured magnetic field. Such switchbacks form (at least, according to most scientists) when closed magnetic loops collide with open magnetic loops and connect with them, during what’s known as an interchange reconnection event. As with good champagne in a bottle, the only way to release energy and plasma from a tangled, closed magnetic loop is to uncork it by breaking it open and reconnecting it with an open field line. These reconnection events generate heat and sling solar material into space — thus warming the corona and accelerating particles in the solar wind.
https://www.quantamagazine.org/how-a-nasa-probe-solved-a-scorching-solar-mystery-20240429/
