New Delhi: A newly developed algorithm analysing 3.7 million proton measurements from 20 close orbits around the Sun by NASA’s Parker Solar Probe has identified
roughly 173,000 unique asymmetrical proton distributions. These particle groups feature a flattened, extended structure resembling a hammerhead shark, representing highly directional streams of hot protons moving significantly faster than the surrounding bulk plasma. Data mapping reveals these proton streams cluster predominantly near the heliospheric current sheet, an immense region where the solar magnetic field reverses in polarity. During the solar minimum, when the current sheet remains relatively flat along the equator, these proton structures appear continuously along the orbital path of the spacecraft.
As solar activity intensifies, and wraps the current sheet into complex, undulating waves, the fast proton groups cluster exclusively where the probe intersects or grazes the folded boundary, providing a direct method to chart the changing magnetic geometry of the Sun. Beyond mapping magnetic boundaries, these specialised populations of protons function as localised reservoirs of energy. Standard principles of thermodynamics dictate that the solar wind should cool rapidly as it expands outwards from the Sun, yet observations show that it maintains an anomalously high temperature, more so than the surface.
Explaining Coronal Heating
How the corona of the Sun is hotter than the Surface is among the biggest unsolved mysteries of the Sun. The phenomenon can be compared to a campfire getting hotter as you walk away. The rapid proton streams possess substantial kinetic energy, that interacts with ambient electromagnetic fields and transfers power into waves, that subsequently heat up the surrounding plasma. Similar non-thermal ion distributions occur with the Earth’s magnetic current sheet as well, with the underlying wave-particle physics and magnetic reconnection processes likely operating universally across diverse plasma environments.
The detection of these structures near coronal mass ejections and magnetic field kinks suggests that current-sheet-related acceleration is a fundamental driver of solar wind heating. This automated diagnostic directly links micro-scale particle dynamics to macro-scale solar structures, resolving long-standing discrepancies in solar cooling models. A paper describing the research has been published in The Astrophysical Journal Letters.
