Astronomers discover exoplanets with magnetic fields

“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 Nice, France, lead author of the study published on Tuesday in the journal 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. 

“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 seven exoplanets ranged up to 25,000kmh, stronger than on Jupiter.

Considering that most of our solar system’s planets have magnetic fields, the researchers said it is not surprising that exoplanets do too. But they said that scientists until now had struggled to come up with convincing evidence.

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

Jupiter’s magnetic field is the largest and most powerful one in our solar system. The seven exoplanets generated magnetic fields smaller than that of Jupiter but comparable to solar system planets in general.

Mercury, Saturn, Uranus and Neptune join Earth and Jupiter as the solar system’s planets generating a global magnetic field. Venus and Mars are the two planets lacking a magnetic field, though Ganymede, a large moon of Jupiter, generates its own magnetic field. Earth’s moon long ago also generated its own magnetic field.

A magnetic field is one of the factors behind whether a planet is able to maintain its atmosphere over long periods of time. For instance, Mars once had a magnetic field, but lost it billions of years ago after its interior cooled, and now has only a tenuous atmosphere and an inhospitable landscape.

“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 in Germany.

“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.”