Astronomers Find Strongest Evidence Yet of Magnetic Fields on Distant Exoplanets

Astronomers have discovered the strongest evidence so far that planets beyond our solar system possess magnetic fields, based on observations of atmospheric winds on seven large and extremely hot gas exoplanets.

The findings, gathered using telescopes in Chile and Hawaii, provide new insights into the nature of exoplanets and suggest that magnetic fields may be a common feature among planets outside our solar system, much like they are among most planets orbiting the Sun.

A magnetic field is an invisible force generated by the movement of electrically conducting material deep inside a planet, typically within a molten core, combined with the planet’s rotation.

Although none of the planets examined in the study are considered suitable for life, scientists note that magnetic fields can be an important factor in maintaining conditions that support habitability on rocky planets such as Earth.

The research focused on seven “hot Jupiters” — giant gas planets similar in size and composition to Jupiter but located extremely close to their host stars. Because of their proximity, one side of each planet permanently faces the star while the other remains in constant darkness, similar to how the Moon always shows the same face to Earth.

The planets studied ranged in mass from approximately that of Jupiter to more than three times larger. Their close orbits expose them to intense heat, creating extreme temperature differences between their day and night sides.

Powerful winds transport heat from the scorching dayside to the cooler nightside. However, researchers found an unexpected pattern.

“What you would expect is that the planets with hotter temperatures would have stronger winds. The more energy you put into the system, the more violent the winds become. But we see the opposite,” said astronomer Julia Seidel of the Observatoire de la Côte d’Azur’s Lagrange Laboratory in France, who led the study published in Nature Astronomy.

“It’s the hottest planets that have the least strong winds mixing the atmosphere. And that’s really strange from what we know of how atmospheres behave,” Seidel said.

She explained that the excess energy received from the host stars must be dissipated through another mechanism.

“That means all that energy that the star puts into the planet’s atmosphere has to be dissipated in a different way. And the only possibility to brake the atmosphere that much that fast is via the magnetic field and its interaction with the moving charged particles of the atmosphere.”

Wind speeds on the exoplanets reached up to 25,000 kilometres per hour, exceeding those observed on Jupiter.

Researchers said that while the existence of magnetic fields on exoplanets is not surprising, obtaining convincing evidence has proven difficult until now.

“We do not look at a singular exoplanet, but we look at a population of them and see a trend emerge,” Seidel said.

The study suggests that the magnetic fields generated by the seven exoplanets are smaller than Jupiter’s powerful magnetic field but comparable to those found on many planets in our solar system.

Among the solar system’s planets, Earth, Mercury, Jupiter, Saturn, Uranus and Neptune all possess global magnetic fields. Venus and Mars do not currently have active global magnetic fields, although Jupiter’s moon Ganymede and Earth’s Moon once generated their own magnetic fields.

Scientists say magnetic fields can help planets retain their atmospheres over long periods. Mars, for example, is believed to have lost its magnetic field billions of years ago as its interior cooled, contributing to the gradual loss of much of its atmosphere and leaving behind a cold, inhospitable environment.

“Although it’s a common misconception that magnetic fields directly determine whether a planet is habitable, they can play an important role in how a planet evolves over time,” said astronomer and study co-author Bibiana Prinoth of the European Southern Observatory.

“Life as we know it relies on having an atmosphere. An atmosphere helps maintain surface pressure, regulate temperature and, on Earth, allows liquid water to exist at the surface.”