Nature’s magnifying glasses can spot the northern lights on distant planets

Einstein’s famous description of spacetime as the fabric of the universe leads to some peculiar facts of nature. Among them: The universe makes its own magnifying glasses.

At the recent 2025 APS Global Physics Summit, astronomers shared how these cosmic magnifying glasses, known as gravitational lenses, could allow us to observe radio waves from planets around other stars. The technique they propose would combine the forces of two upcoming powerhouse telescopes, NASA’s Roman Space Telescope and the international Square Kilometer Array, to double the number of new exoplanets Roman will find.

This technique is “a completely new way of detecting and studying exoplanets,” says lead author and presenter Fatemeh Bagheri, an astronomer at NASA’s Goddard Space Flight Center. “We are tapping into a new observational window that could provide more direct and detailed information about these distant worlds.”

Bagheri’s new technique relies on a well-established way of detecting exoplanets: gravitational microlensing. Gravitational lensing happens when light from a star has to bend around a massive object on its way to our telescopes, making the star appear magnified from our perspective. This natural magnification zooms in on distant objects that we otherwise wouldn’t have any chance of detecting, because they’d be too faint and small without the lens. The James Webb Space Telescope has captured snapshots of the most distant galaxies ever seen, thanks to lensing.

Microlensing is essentially the same process on a smaller scale. When light from a background star is lensed by a star closer to us — and that nearby star has a planet around it — the planet’s gravity will add an extra bend to the background star’s light. In practice, the lensing planet adds a blip on top of the signal you’d expect from a typical lone star. The Roman Space Telescope, expected to launch by May 2027, will excel at this planet-hunting technique and is expected to find about 1,400 exoplanets with microlensing. (Roman is also going to be good at the transit method. Scientists predict it will make over 100,000 new transiting exoplanet detections — more than fifteen times the total number of exoplanets discovered to date.)

Typically, microlensing looks for indirect evidence of a planet around the star doing the lensing. But Bagheri’s proposed method would directly record emission from a planet around the background star — “a distinct approach compared to the one used by the Roman team,” she says.

When a background star is magnified by a gravitational lens, a planet’s emission — whether infrared, radio, or any other part of the electromagnetic spectrum — is magnified, too. In Bagheri’s plan, Roman will spot a microlensing event in the infrared, then trigger a notification for astronomers to point their radio telescopes at that target for follow-up.

Why look at a planet with radio waves? Radio waves are just long wavelengths of light, and stars simply don’t emit a lot of them, making it easier to spot a planet amidst the light from stars.

Radio waves are also a unique window into a planet’s magnetic field, which can generate radio waves in aurorae. Planetary aurorae, like Earth’s northern lights, emit radio waves when high-energy particles from a nearby star interact with a planet’s magnetic field. By observing radio emission from a planet, astronomers can infer the strength of the planet’s magnetic field. A strong magnetic field is a prerequisite for a stable atmosphere — and as a result, the possibility of extraterrestrial life.

“A strong magnetic field helps protect the planet’s atmosphere from being stripped away by the star's radiation, so the nature of the radio signals could tell us whether the planet’s atmosphere is stable or subject to erosion,” says Bagheri. And because magnetic fields are generated from a planet’s molten metal core, these radio signals can also shed light on a planet’s internal structure and composition.

Astronomers will need one more tool to record the faint radio signals of distant exoplanet aurorae: the SKA. This observatory consists of a vast forest of over 100,000 radio antennae in Australia and South Africa, and is set to come online around 2027 alongside Roman’s launch. It will be “the most advanced radio telescope we will have in terms of frequency range and sensitivity,” says Bagheri.

Roman and the SKA’s similar launch date makes Bagheri’s plan possible, a stroke of serendipity. Better still, the stars sometimes literally align to magnify the faint emissions of exoplanets. According to her calculations, radio follow-up observations from microlensing will double the number of exoplanets Roman expects to reveal, adding another 1,300 discoveries to the list.

“This approach could drastically improve how we discover exoplanets,” says Bagheri. “Not only could it help us identify exoplanets that we might otherwise miss, but it could also give us insights into their environments, their potential for supporting life, and their magnetic properties — important factors for understanding how planets evolve and interact with their stars.”