Astronomers Report First Robust Measurement of Magnetism on Exoplanets, Inferred From Strange Winds on Seven Hot Jupiters
An ESO and Gemini North team found winds on seven hot Jupiters slow as the planets get hotter, a pattern best explained by planet-wide magnetic fields.
Overview
Astronomers have reported what they describe as the first robust measurement of magnetism on planets outside the Solar System, based on the behavior of winds on a sample of scorching gas giants. According to the European Southern Observatory, the observations revealed that the winds on these planets are most likely governed by magnetic fields, providing the first robust measurement of magnetism on planets outside the Solar System. The result was published in the journal Nature Astronomy on June 2, as reported by Space.com.
What We Know
The team measured wind speeds on seven very hot, Jupiter-like exoplanets, according to the European Southern Observatory. To do so, the researchers used the European Southern Observatory’s Very Large Telescope and the Gemini North telescope, drawing on data from the ESPRESSO instrument on the VLT, in the Chilean Atacama Desert, and from a similar instrument on Gemini North in Hawaiʻi, as detailed by Phys.org.
The winds they clocked were extreme. According to the European Southern Observatory, wind speeds in the sample ranged from around 7,200 km/h to over 25,000 km/h; in comparison, the fastest winds measured on Jupiter reach speeds of around 1,500 km/h. Space.com put the same figures at between 4,470 miles per hour and 15,530 mph, against roughly 930 mph for Jupiter’s fastest winds.
The key clue was not the raw speed but a pattern. Across the sample, the hotter the planet, the slower the wind, according to the European Southern Observatory. That relationship runs against expectations. “This is totally counter-intuitive because, all things being equal, hot planets have more energy to accelerate the winds!” said Vivien Parmentier of Laboratoire Lagrange, as quoted by Phys.org.
The researchers concluded that the most consistent explanation for this mystery is the presence of planet-wide magnetic fields, since these fields can work as a brake, slowing down the motion of charged particles in the atmosphere, according to the European Southern Observatory. Because the slowdown scales with temperature, the team argues the wind speeds can be used to infer the strength of these exoplanets’ magnetic fields, as reported by Space.com.
“This breakthrough opens a completely new window on exoplanet research,” said Julia Seidel of Laboratoire Lagrange at the Observatoire de la Côte d’Azur, according to the European Southern Observatory.
What We Don’t Know
The measurement is indirect. The team did not detect magnetic fields directly but inferred their presence as the best explanation for an otherwise puzzling wind pattern, according to the European Southern Observatory. The published coverage does not identify the seven planets individually, and Space.com notes none of the worlds were named in its report.
Whether the same technique extends to smaller, cooler, potentially habitable worlds remains an open question for future instruments. The team eagerly anticipates the arrival of ESO’s Extremely Large Telescope, which will help to characterise not only large, Jupiter-like exoplanets but also smaller ones like Earth, possibly even detecting gases that could produce aurorae on these distant worlds, according to the European Southern Observatory.
Why It Matters
Magnetic fields shape a planet’s atmosphere and may help shield it from stellar radiation, but they have been effectively impossible to measure beyond the Solar System. By turning anomalous wind speeds into a proxy for magnetism, the new work offers a route to studying exoplanet magnetic fields without detecting them directly. One co-author framed the implication in vivid terms: “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,” said Bibiana Prinoth of ESO Garching, according to the European Southern Observatory.