The galaxy’s hottest giant planets are expected to have the fastest winds. Hot Jupiters, a class of exoplanets, are among the hottest planets discovered, boasting intense atmospheric currents as they orbit extremely close to their host stars. Some are even evaporating from the intense heat.
However, a recent study of seven hot Jupiters shows surprisingly slow wind speeds, contrary to astronomers’ expectations. According to a team led by astronomer Julia Seidel from the CĂ´te d’Azur Observatory in France, a magnetic field might be the reason behind this unexpected slowdown.
If confirmed, these slow winds could provide the strongest evidence yet of magnetic activity on planets beyond our Solar System.
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>“This breakthrough opens a completely new window on exoplanet research,” Seidel remarks. “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.”
Hot Jupiters are among the most intriguing exoplanets in the Milky Way. Due to their close proximity to their stars, they can complete an orbit in less than a day. These planets are typically tidally locked, with one side always facing the star in daylight and the other in perpetual darkness, creating extreme weather conditions.
These planets reach equilibrium temperatures of several thousand degrees, driving intense atmospheric circulation. While direct measurements of magnetic fields on exoplanets are not possible, past studies have used vaporized iron in their atmospheres to gauge wind speeds.
Recognizing that magnetic fields can slow down electrically charged gases, researchers have hypothesized that wind speeds on hot Jupiters could indicate magnetic field activity.
Using the MAROON-X instrument on the Gemini North telescope and the ESPRESSO instrument on ESO’s Very Large Telescope, researchers measured wind speeds across seven hot Jupiters. These winds, ranging from 2 to 7 kilometers per second, are significantly faster than any in our Solar System, where Jupiter’s winds top out at about 0.4 kilometers per second.
The intriguing discovery is the inverse relationship between wind speed and temperature on these exoplanets. The hotter the planet, the slower the winds.
frameborder=”0″ allow=”accelerometer; autoplay; clipboard-write; encrypted-media; gyroscope; picture-in-picture; web-share” referrerpolicy=”strict-origin-when-cross-origin” allowfullscreen>Other theories have been proposed for the slower winds on hot Jupiters, but researchers assert that these would likely show the opposite trend, with wind speeds increasing with temperature.
“This is totally counterintuitive because, all things being equal, hot planets have more energy to accelerate the winds!” says astronomer Vivien Parmentier of CĂ´te d’Azur Observatory. “Something must happen that slows down the wind speeds for hotter objects.”
The researchers believe magnetic fields are the likely cause and have inferred the magnetic field strength based on their observations. These hot Jupiters are estimated to have magnetic fields of only a few gauss, comparable to Jupiter’s.
Further observations are needed to confirm the team’s findings, as these are based on proxy measurements.
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Nonetheless, this discovery highlights the progress made in understanding alien worlds, shifting from studying individual planets to analyzing statistical patterns.
“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 colorful displays of green, pink, and purple,” says astronomer Bibiana Prinoth. “I like to imagine that some of these worlds have a sky filled not only with stars, but with vast curtains of colorful light dancing across a planet that’s half in perpetual day and half in endless night.”
The research has been published in Nature Astronomy.
