Predictions
Parker Solar Probe carries four instrument suites, and each is credited with several groundbreaking discoveries:
The Solar Wind Electrons Alphas and Protons investigation, or SWEAP, is responsible for sampling the solar atmosphere. During its first pass close enough to cross the boundary where solar material anchored to the sun first escapes and becomes the solar wind—known as the Alfvén critical surface—the probe recorded key information about the boundary's shape and discovered that rather than resembling a smooth ball, the Alfvén critical surface is wrinkled with spikes and valleys. SWEAP established that the wrinkles stemmed from coronal streamers—giant plumes of solar material rising through the sun's atmosphere. Streamers have long been observed by sun-watching spacecraft near Earth, but have never been measured directly. "The results are reshaping what we know about the sun's atmosphere and how it transforms into the solar wind," Raouafi said.
The Wide-Field Imager for Parker Solar Probe, or WISPR, is discovering the dust-depletion zone, a region around the sun where scientists predict that dust particles should get hot enough to sublimate and thus disappear. The WISPR instrument observed light reflected from dust dimming at about 19 solar radii (8.2 million miles from the sun). Models of the results suggest that a dust-free zone should exist starting at about 5 solar radii (2.2 million miles from the sun). "Discovering the dust-depletion zone around the sun is not only historical but also insightful on the environment near the sun and other stars," said Mark Linton, WISPR principal investigator from the Naval Research Laboratory.
FIELDS is tracking down the origins of switchbacks, rapid reversals in the sun's magnetic field that reverse direction like a zig-zagging mountain road. During the probe's sixth flyby of the sun, FIELDS data revealed that the switchbacks aligned with magnetic "funnels" on the solar surface. These funnels emerge from between structures called supergranules—giant bubbles on the sun in which hot plasma from the solar interior rises, spreads out across the surface, cools, and then sinks back down. The magnetic geometry of these regions suggests that magnetic reconnection powers the solar wind. But while the findings locate where switchbacks are made, researchers are still digging into the question of how they're formed.
The Integrated Science Investigation of the sun, or ISʘIS, is rewriting the book on solar energetic particles, the most energetic particles that escape the sun. Measured near Earth, SEP events are relatively rare and hard to predict. But detecting SEPs close to the sun, ISʘIS has found that SEPs are much more common than expected, that they contain a wider range of types of particles than expected, and that their paths from the sun are not as direct as previously thought—they can be disrupted by the switchbacks and can at times follow a path twice as long as expected. By measuring these events so close to the sun, ISʘIS is detecting events so small that all trace of them is lost before they reach Earth, helping scientists develop a fuller picture of where they come from and how they're accelerated away from the sun.
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