Astronomers have found the strongest evidence yet that planets beyond our solar system possess magnetic fields, solving an important question in the study of distant worlds.
Using the European Southern Observatory’s Very Large Telescope (ESO’s VLT) and the Gemini North telescope in Hawaii, researchers measured wind speeds on seven extremely hot, Jupiter-like exoplanets.
The findings suggest the winds are likely shaped by planetary magnetic fields, providing what scientists describe as the first robust evidence of magnetism on planets outside the solar system.
Julia Seidel, lead author of the study, said: ‘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.’
Magnetic fields are known to play a crucial role in shaping planetary atmospheres.
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Earth’s field helps protect the atmosphere and is considered essential to maintaining conditions suitable for life. Other planets in the solar system, including Jupiter and Saturn, also possess strong magnetic fields.
However, despite years of study, direct measurements of magnetic field strength on exoplanets had not previously been achieved.
Researchers in this study, published in Nature Astronomy, did not initially set out to measure magnetism.
Instead, they focused on atmospheric winds across seven exoplanets orbiting distant stars.
These gas giants are similar in size to Jupiter but are tidally locked, meaning one side permanently faces their host star.
This creates extreme temperature differences between a scorching day side and a freezing night side, driving powerful atmospheric winds.
Wind speeds in the sample ranged from around 7,200 km/h (4,500mph)to more than 25,000 km/h (15,500,ph) By comparison, Jupiter’s fastest winds reach approximately 1,500 km/h (930mph).
‘In the beginning we set out to check if the atmospheric winds behaved the same way for all hot planets,” said Seidel, who is an astronomer at the Laboratoire Lagrange, Observatoire de la Côte d’Azur, France.
The team used data from the ESPRESSO instrument on ESO’s VLT in Chile’s Atacama Desert, alongside a similar instrument on Gemini North, part of the International Gemini Observatory.
However, when the researchers compared wind speeds with planetary temperature, they observed an unexpected pattern: hotter planets tended to have slower winds.
‘This is totally counter intuitive 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,’ study co-author Vivien Parmentier said.
The most plausible explanation, the team concluded, is the presence of global magnetic fields.
These fields can act as a drag on atmospheric motion by slowing charged particles, effectively braking the winds.
This allowed researchers to estimate the strength of the magnetic fields on each planet, which they found to be comparable to those within our own Solar System – around four times the strength of Saturn’s field or roughly half that of Jupiter’s.
Such magnetic fields could influence more than just atmospheric circulation. On Earth, magnetic interactions between solar particles and the atmosphere produce auroras in the polar regions.
‘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,’ study co-author Bibiana Prinoth said.
On these distant exoplanets, scientists believe similar – and potentially far more intense – auroras could occur.
Future observations with ESO’s Extremely Large Telescope are expected to help researchers study not only gas giants but also smaller, Earth-like planets, and potentially detect atmospheric signatures linked to auroral activity.
Prinoth said: ‘I like to imagine that some of these worlds have a sky filled not only with stars, but with vast curtains of colourful light dancing across a planet that’s half in perpetual day and half in endless night.’