The first direct measurements of exoplanet magnetic fields reveal that ultra-hot Jupiters possess strong magnetism that shapes their atmospheres and may provide new insights into planetary habitability.
Astronomers have achieved a major advance in the study of worlds beyond our Solar System by estimating the strength of the magnetic fields surrounding seven ultra-hot Jupiters. The findings, published in Nature Astronomy, suggest that some of the hottest known exoplanets possess magnetic fields comparable in strength to those found on planets in our own Solar System.
“This breakthrough opens a completely new window on exoplanet research. It’s the first time we can compare the magnetic environments of other worlds — a key step toward ultimately understanding which planets can stay alive, keep their water, and perhaps even, one day, host life as we know it,” says Julia Seidel, an astronomer at the Laboratoire Lagrange, Observatoire de la Côte d’Azur, France, and lead author of the study.
Earth’s magnetic field serves as a protective barrier, helping prevent cosmic radiation from stripping away the atmosphere and supporting conditions suitable for life. Other planets in our Solar System, including Jupiter and Saturn, also have magnetic fields. Until now, however, astronomers had not been able to directly estimate the strength of magnetic fields on planets orbiting other stars.
Tracking Extreme Winds on Ultra-Hot Jupiters
The researchers were originally studying atmospheric winds rather than magnetic fields. They measured wind speeds on seven giant exoplanets similar to Jupiter that orbit very close to their stars and are tidally locked. Like the Moon, which always shows the same face to Earth, these planets permanently keep one side pointed toward their star. As a result, they have an intensely hot day side and an extremely cold night side.
The dramatic temperature contrast creates unusual weather conditions with exceptionally powerful winds. Wind speeds on the studied planets ranged from about 7,200 kilometers (4,400 miles) per hour to more than 25,000 kilometers (15,500 miles) per hour. For comparison, Jupiter’s fastest known winds reach roughly 1,500 kilometers (900 miles) per hour.
To make these measurements, the team analyzed observations from the MAROON-X instrument on the Gemini North telescope in Hawaiʻi, one of the two telescopes that make up the International Gemini Observatory, which is partly funded by the U.S. National Science Foundation (NSF) and operated by NSF NOIRLab. They also used data from the ESPRESSO instrument on ESO’s Very Large Telescope (VLT) in Chile’s Atacama Desert. These high-resolution instruments allowed researchers to track atmospheric motion by identifying the light signatures of specific chemicals and following their movement through the planets’ atmospheres.
“The stability of MAROON-X makes it a powerful tool for detecting the subtle motion of Earth-sized planets around other stars, as well as tracing changes in the atmospheres of exoplanets depending on orbital phase,” says Andreas Seifahrt, Associate Director of Development for Gemini Observatory and study co-author. “The unexpected discovery that resulted from studying the winds of these seven ultra-hot Jupiters shows that there is even more that we can learn from the data. MAROON-X provides a world-class capability for these studies.”
Magnetic Fields Explain the Wind Mystery
When the team compared wind speeds with planetary temperatures, they uncovered an unexpected trend. Instead of producing faster winds, higher temperatures were associated with slower winds.
“This is totally counterintuitive because, all things being equal, hot planets have more energy to accelerate the winds! Something must happen that slows down the wind speeds for hotter objects,” says study co-author Vivien Parmentier, a professor at the Laboratoire Lagrange.
According to the researchers, the most likely explanation is the presence of strong magnetic fields spanning the entire planet. These fields can act like a braking mechanism, slowing the movement of charged particles in the atmosphere. Using this relationship, the team was able to estimate the magnetic field strength of each planet. The results indicate fields roughly four times stronger than Saturn’s magnetic field and about half as strong as Jupiter’s.
Strong magnetic fields may influence much more than atmospheric winds. “Here on Earth, we know the beauty of the northern and southern lights, where particles from the Sun hit our magnetic field and are guided toward the poles, colliding with gases in the atmosphere to produce colourful displays of green, pink, and purple,” explains study co-author Bibiana Prinoth, a former PhD student at Lund University, Sweden, now an astronomer at ESO in Garching, Germany. Similar magnetic interactions on these distant planets could generate even more spectacular auroras.
Reference: “Magnetic field strengths of hot giant exoplanets consistent with Solar System values” by Julia V. Seidel, Vivien Parmentier, Bibiana Prinoth, Thea Hood, Nishil Mehta, Valentin De Lia, Konstantin Batygin, Tristan Guillot, Ragnar Van den Broeck, Hayley Beltz, Brian Thorsbro, Florian Debras, Daniel D. B. Koll, Thaddeus D. Komacek, Emily Rauscher, Lorenzo Pino, Matteo Brogi, Joost P. Wardenier, Jacob L. Bean, Björn Benneke, Jean-Michel L. B. Désert, Pablo Drake, Siddharth Gandhi, Mark Hammond, David Kasper, Michael R. Line, Elspeth K. H. Lee, Stefan Pelletier, Andreas Seifahrt, Adrien Simonnin, Peter C. B. Smith and Kevin B. Stevenson, 2 June 2026, Nature Astronomy.
DOI: 10.1038/s41550-026-02870-1
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