Cosmic dust could play key role in cracking long-standing mystery of solar corona heating

A researcher at The University of Alabama in Huntsville (UAH), a part of The University of Alabama System, has published a new study in The Astrophysical Journal suggesting that tiny charged dust grains near the sun may significantly influence how energy moves through the solar corona, the outer atmosphere of the sun. The discovery potentially rewrites how scientists understand why the corona is millions of degrees hotter than the surface of the sun itself.

Conducted using data from NASA’s Parker Solar Probe (PSP), the work shows that dust, long assumed to be largely irrelevant so close to the sun, can alter the behavior of key plasma waves that transport energy through space. By changing how these waves travel and dissipate energy, dust may help determine where and how solar heating occurs in the corona and young solar wind.

The study’s lead author, Syed Ayaz, is a graduate research assistant in the UAH Center for Space Plasma and Aeronomic Research (CSPAR).

“The discovery of dust in the young solar wind by Parker Solar Probe allowed Syed to open up an entirely new and unexpected area of study in solar physics,” says Dr. Gary Zank, distinguished professor of space science at UAH and CSPAR director.

“This is very exciting, and Syed realized very quickly that the presence of dust could change how we view the long-standing and open problem of how to heat the solar corona to more than a million degrees. The results he obtained in his preliminary study already suggest that a surprising new paradigm may be emerging. Syed has done outstanding work that will have a significant impact on understanding of the physics of the solar corona.”

The solar corona is a huge region of extremely hot, thin plasma that extends millions of kilometers into space and is much hotter than the surface, or photosphere, of the sun, which reaches only about 5,500°C (9,900°F), while the corona can reach 1–3 million°C or more.

“The higher temperature of the sun’s corona remains one of the major unsolved problems in heliophysics,” Ayaz explains. “For decades, researchers have focused mainly on how electrons, ions, magnetic fields and plasma waves transport and dissipate energy in the solar atmosphere. Kinetic Alfvén waves are especially important because they can carry electromagnetic energy through the corona and transfer that energy to particles, helping to heat and accelerate the plasma.”

What sets the new study apart is the introduction of dust grains into models that have traditionally treated the near-sun environment as only a mix of electrons, ions and magnetic fields.

“Our work adds a new ingredient to this picture: dust grains,” Ayaz says. “Before the Parker Solar Probe, dust was not usually considered an active part of coronal heating models because dust grains—a million times more massive than electrons/ions—were not expected to survive the high temperature of the solar corona.”

Instead, data from the PSP revealed something unexpected: dust is still present and active far closer to the sun than previously thought.

“What surprised me most was that the PSP could reveal so much about dust, even though it does not carry a dedicated dust detector on board,” Ayaz notes. “When tiny dust grains strike the spacecraft at high speed, they vaporize and produce small clouds of charged particles. These impacts appear as sharp voltage spikes in the FIELDS antennas, allowing the whole spacecraft itself to act, in effect, like a dust detector.”

Recording a cosmic dust-up

The FIELDS instrument is a suite of devices that measure electric fields, magnetic fields, plasma waves and radio emissions in the solar corona and solar wind. These measurements indicate that dust is not only surviving in the inner heliosphere but also interacting with plasma processes in measurable ways.

“This matters for solar physics because charged dust grains are not just passive particles,” Ayaz says. “Once dust grains acquire an electric charge through processes such as photoemission and plasma collection, they interact with electric and magnetic fields, influence plasma waves and modify how energy is transported and dissipated.”

A central finding of the study is that dust affects kinetic Alfvén waves—important carriers of energy in space plasmas—in two competing ways depending on whether dust mass or dust charge dominates.

“Our study shows that dust plays two distinct roles in the way energy moves through the sun’s atmosphere,” Ayaz says. “Dust mass acts like an added inertia in the plasma. This tends to slow kinetic Alfvén waves and allows their energy to be carried over larger distances before it is dissipated. Dust charge, on the other hand, strengthens the interaction between the wave, the electric field and charged particles.”

These opposing effects in turn could determine where solar energy is deposited. “If dust mass dominates, wave energy may travel farther into the corona or young solar wind,” Ayaz says. “If dust charge effects dominate, the energy may be released more locally as particle heating.”

The findings challenge long-standing assumptions in solar physics models that typically exclude dust as a dynamic participant in coronal heating.

“Most models of solar heating and particle acceleration treat the near-sun environment as a plasma made mainly of electrons, ions and magnetic fields,” Ayaz says. “Those ingredients are still essential, but our research shows that charged dust grains also influence the physics in this region.”

In addition, the work raises broader questions about the structure of the near-sun environment and how energy is transported across it.

“One of the most exciting questions is whether dust near the sun is only a tracer of the inner heliospheric environment, or whether it is actually an active ingredient in the physics of coronal heating and solar-wind acceleration,” Ayaz says. “PSP has already shown that the near-sun dust environment is more surprising and variable than expected. Future PSP observations are especially important because each closer encounter gives us a better look at a region that has never been sampled in this way before.”

“It’s exciting to see innovative ideas emerge from our graduate researchers,” says Dr. Lingling Zhao, an assistant professor in the UAH Department of Space Science. “This study highlights how fresh perspectives and new observations can lead to unexpected discoveries.”

Looking ahead, Ayaz envisions future missions with dedicated dust and plasma instruments that could help determine whether dust is a missing piece in solving the coronal heating problem.

“Missions beyond Parker, especially those with dedicated dust detectors and multi-spacecraft plasma-wave measurements, could go even further,” Ayaz concludes. “The bigger question is fascinating: Is dust simply passing through the near-sun environment, or is it helping shape how electromagnetic energy becomes heat and solar-wind motion?”

Who’s behind this story?

Robert Egan

Bachelor’s in mathematical biology, Master’s in creative writing. Well-traveled with unique perspectives on science and language.

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