A research team from the Department of Physics at the University of Santiago de Chile (Usach) published a study that provides unprecedented insights into the thermodynamic behavior of the solar wind in the vicinity of the Sun. The paper, titled “The effect of expansion and instabilities in the thermodynamic regulation of the young solar wind plasma”, was accepted on August 9, 2026, by Astronomy & Astrophysics, one of the world’s most prestigious journals in astronomy and astrophysics.
The research is led by Dr. Matilde Coello-Guzmán as the lead author, with the participation of Dr. Víctor Pinto—both from the USACH Department of Physics—along with Dr. Roberto Navarro from the University of Concepción and Dr. Pablo Moya from the Planets group in the Department of Physics at the University of Chile.
Both USACH researchers are part of the Heliophysics and Space Weather Group, which specializes in the study of the Earth’s magnetosphere, the radiation belts, the coupling between the solar wind and the magnetosphere, and the dynamics of the solar wind, using satellite data and ground-based observations. The group also develops machine learning and artificial intelligence tools for space weather forecasting and collaborates on Chile’s first national space weather monitoring platform.
A “Younger” and Uncharted Solar Wind
The solar wind is a continuous stream of charged particles ejected by the Sun into space. Its behavior near Earth—at a distance of 1 astronomical unit (AU)—is well documented thanks to decades of satellite observations. What has remained far more elusive until now is how the solar wind behaves immediately after leaving the Sun, before its long journey through space fully shapes its dynamics.
Thanks to NASA’s Parker Solar Probe—the closest human-made object to the Sun—the research team extended their observations to within less than 0.1 AU of the solar surface. This breakthrough drastically surpasses the previous observation limit of 0.3 AU, allowing scientists to analyze the solar wind in its earliest stages.
“For solar wind ions located 1 astronomical unit away, the types of instabilities present are well known thanks to the large number of measurements that have been possible over the past few decades. Thanks to the novel data from the Parker Solar Probe, we were able to extend that characterization to the region near the Sun,” explains Dr. Coello-Guzmán.
The study focuses on plasma instabilities—physical processes that govern the behavior of ionized gas in space. These instabilities transfer energy from the thermal motion of charged particles into oscillations in surrounding electromagnetic fields, ultimately constraining the conditions under which the solar wind can exist.
The results reveal a striking contrast between early solar wind dynamics and those observed near Earth. “We verified theoretical predictions showing that when magnetic pressure outweighs kinetic pressure, the resulting instabilities propagate in a parallel direction,” the researcher explains. “This marks a clear shift from conditions at 1 AU, where kinetic pressure dominates over magnetic pressure, favoring oblique-type instabilities.”
To reach these conclusions, the team combined predictions from quasi-linear theory with high-precision numerical modeling. This dual approach allowed researchers to calculate the exact thresholds of kinetic pressure, magnetic pressure, and free energy that trigger these plasma instabilities—effectively bridging direct satellite observations with fundamental theoretical physics, two methodologies that are typically developed in isolation.
Collaborative and Open-Access Science
The study was made possible through a collaboration between the Department of Physics at Usach, the Plasma Group at the University of Concepción, and the PlaNets Group at the University of Chile’s Faculty of Sciences, alongside open-source data from NASA. Funded by ANID’s Fondecyt program and Usach’s Dicyt Postdoctoral Fund, the research has been published as open access for the global scientific community.
“Thanks to the public nature of NASA’s data, we were able to conduct this groundbreaking research entirely in Chile, and we published it in an open-access journal because we believe in knowledge that is free and available to all of society,” says Dr. Coello-Guzmán.
The team hopes these findings will contribute to a more comprehensive macroscopic understanding of the solar wind, elevating Chilean research in global discussions on space weather physics. This milestone has already paved the way for new international partnerships, with the team currently investigating additional thermodynamic processes that regulate the solar wind near the Sun.