The Sun presents what appears to be an anomaly: its corona, the outer atmosphere, reaches temperatures of several million degrees, while its visible surface, the photosphere, is much cooler, at about 5,500 °C (about 9,932 °F). This phenomenon, observable during total eclipses, has intrigued scientists for decades. Traditional explanations focused on electrons, ions, and magnetic fields, but now a new clue has emerged: cosmic dust.
Recently, the Parker Solar Probe, which approached to within 6.1 million kilometers (about 3.8 million miles) of the Sun, detected unexpected voltage spikes. These signals come from the impact of microscopic dust grains hitting the probe at high speed. Until now, it was thought that dust did not survive in the corona, but these observations change the picture.
Credit: NASA GSFC/CIL/Brian Monroe These grains acquire an electrostatic charge as they travel through the solar wind. This charge allows them to interact with magnetic fields and Alfvén waves—oscillations in the plasma that propagate along field lines. The team of researcher Syed Ayaz, from the University of Alabama in Huntsville, published these results in
The Astrophysical Journal in July 2026.
Two opposing mechanisms are at play. On one hand, the mass of the dust grains adds inertia to the plasma, which can carry the energy of Alfvén waves over greater distances. On the other hand, the electrical charge of the grains amplifies interactions between the charged particles of the plasma, the waves, and the solar magnetic field, releasing energy locally in the form of heat.
The balance between these two effects determines where and when energy is deposited in the corona. If the mass effect dominates, energy propagates further; if the charge effect prevails, it heats locally. This balance could explain the extreme temperatures observed in some regions of the corona.
Future solar missions will now have to take dust into account. Specialized detectors will be able to measure its properties near the Sun. As Syed Ayaz puts it, the big question is whether dust is merely a foreign body or whether it actively contributes to transforming electromagnetic energy into heat and motion in the solar wind.