Earth’s magnetic field does more than point compass needles in the same direction. It also helps maintain some of Earth’s life-sustaining atmosphere by deflecting high-energy particles and plasma that are regularly expelled from the sun. Now researchers have identified a promising Earth-sized planet in another solar system as a prime candidate for the magnetic field – YZ Ceti b, a rocky planet orbiting a star about 12 light-years from Earth.

Researchers Sebastian Pineda and Jackie Willadsen observed the repetitive radio signal emanating from the star AI Ceti using the Carl Jinsky Very Large Array radio telescope at the US National Science Foundation’s National Radio Astronomy Observatory. Pineda and Willadsen’s research to understand magnetic field interactions between distant stars and planets orbiting them is supported by NSF. Their research was published today (April 3) in the journalism. Nature Astronomy.

“Studying potentially habitable or habitable worlds in other solar systems depends in part on our ability to determine whether rocky, Earth-like exoplanets do indeed have magnetic fields,” says Joe Pesce, program director of the NSF’s National Radio Astronomy Observatory. “This study not only shows that this particular rocky exoplanet likely has a magnetic field, but also offers a promising method for finding new ones.”

Pineda, an astrophysicist at the University of Colorado, explains that a planet’s magnetic field can prevent that planet’s atmosphere from being eroded over time by particles ejected from its star. “Whether a planet with an atmosphere will survive may depend on whether the planet has a strong magnetic field.”

Radio signal from another star

“I see things that no one has seen before,” recalls Willadsen, an astronomer at Bucknell University, when he first picked up the radio signal while streaming data at his home over the weekend.

“We saw the first surge and it looked great,” Pineda says. “When we saw it again, it made a lot of sense, okay, maybe we really have something here.”

The researchers hypothesize that the stellar radio waves they detected were produced by the interaction between the exoplanet’s magnetic field and its orbiting star. However, such radio waves must be very strong to be detected at great distances. While magnetic fields have been detected on huge Jupiter-sized exoplanets before, a relatively small Earth-size exoplanet requires a different technique.

Willadsen explains that because magnetic fields are invisible, it’s hard to tell if they really exist on a distant planet. “We’re looking for a way to see them,” he says. “We’re looking for planets that are very close to their stars and similar in size to Earth. These planets are too close to their star to be habitable, but because they’re so close, the planet seems to be piercing through a lot of things moving away from the star.

“If the planet has a magnetic field and it penetrates enough stellar material, it will cause the star to emit bright radio waves.”

The small red dwarf star YZ Ceti and its famous exoplanet YZ Ceti b make a perfect pair because the exoplanet is so close to the star that it completes a full orbit in just two days. (For comparison, the shortest planetary orbit in our solar system, Mercury’s, is 88 days.) As the plasma from the YZ Ceti leaves the planet’s magnetic “plow”, it interacts with the magnetic field of the star itself, generating powerful radio waves. Enough to observe on Earth.