By timing winds on seven ultra hot gas giants, Jupiter sized planets locked in close orbit around their stars, scientists inferred the strength of magnetic shields on worlds beyond our solar system.
For the first time, astronomers have obtained reliable readings of magnetic field strength on planets beyond the solar system, using a proxy that is easier to observe from Earth: the speed of winds on the planet's day side. The result, published in Nature Astronomy (DOI: 10.1038/s41550-026-02870-1) and announced by the European Southern Observatory, comes from a survey of seven ultra-hot gas giants, Jupiter-sized worlds that orbit so close to their stars that one hemisphere is permanently scorched while the other is permanently frozen.
The work was led by Julia Seidel of the Laboratoire Lagrange at the Observatoire de la Côte d'Azur, who used two of the world's largest ground-based observatories: the European Southern Observatory's Very Large Telescope in Chile's Atacama Desert, and the Gemini North telescope on Hawaii's Mauna Kea. "Our method opens a new window into the magnetic environment of exoplanets," Seidel said in the ESO release announcing the finding.
That release closes with a tail clause, "and may one day help us understand whether any of them could, perhaps even, one day, host life," that outruns what the data can support. The seven planets in the sample are tidally locked hot Jupiters, gas giants that circle their stars in days rather than years, not rocky Earth-sized worlds. The magnetic field strengths were inferred from atmospheric models rather than measured directly, and the technique has so far been demonstrated by one team on one population. The result is a measurement milestone, not a habitability claim.
The method works because of a peculiar feature of these worlds. On a tidally locked hot Jupiter, the temperature contrast between the day side and the night side can exceed a thousand kelvins. That contrast drives fierce winds, with air rushing from the hot hemisphere to the cold one in an attempt to equalize the heat. A planetary magnetic field pushes back against those winds, slowing them down. By measuring the wind speed and comparing it to the wind speed an unmagnetized atmosphere would produce, the team could infer the strength of the braking field.
The team measured winds ranging from about 7,200 km/h to more than 25,000 km/h — far faster than Jupiter's fastest known winds of roughly 1,500 km/h. The derived field strengths are roughly four times greater than Saturn's and about half that of Jupiter, comparable to the magnetic field strengths found on giant planets in our own solar system. The detection is indirect, but it is the first time astronomers have obtained numerical magnetic field strengths on planets outside the solar system, and the first time a single technique has been applied consistently to more than one exoplanet.
Why magnetic fields matter, beyond the physics: in the solar system, the magnetic fields of Earth, Jupiter, and Saturn help shield their atmospheres from being slowly stripped away by the solar wind, the stream of charged particles flowing outward from the Sun. A planet that can keep its atmosphere is a planet that can keep its water and, over geological timescales, the chemical preconditions for life. A reliable way to measure these fields on exoplanets is therefore a building block for the next generation of habitability models, though not a measurement of habitability itself.
The next test is replication. Other teams will need to apply the wind-braking method to independent samples of hot Jupiters, and to cooler giant planets where the day-night contrast is less extreme. Eventually, the technique may extend to smaller worlds, but for now, the strongest reading available comes from a class of planets where the signal is loud and the field is plausibly present, a useful starting point for a new channel into one of the hardest measurements in exoplanet science.