A streetlamp flickers as someone walks past. That's roughly how our nearest star, Proxima Centauri, behaves: it flares in response to the motion of its planets.
Astronomers observed the star with a highly sensitive instrument, the ESPRESSO spectrograph. It captures light and splits it into colors, much like a prism. The team noticed that the tiny planet Proxima d (about the size of Mars) makes the star flare at precise moments along its orbit. The planet seems to tug on a magnetic thread linking it to the star, which answers with a brief, bright spark. This is the first time such behavior has been seen for a rocky planet outside our solar system.
The second planet, Proxima b (about the size of Earth), acts differently. It doesn't make the star flare more often, but it changes the flares' strength. If Proxima d is a child yanking on a cord, Proxima b is like someone slowly turning a dimmer switch. The researchers even calculated the magnetic field of planet d — roughly between 3 and 280 gauss. For comparison, Earth's field is about 0.5 gauss, and a fridge magnet is around 100 gauss. So the planet could be a true magnetic dwarf.
This discovery is a first step toward listening to the magnetic conversations of distant worlds. In the future, such connections might help us determine whether a planet has a protective magnetic field. That field shields it from stellar wind, like an umbrella from rain, and thus helps us gauge the chances for life under a foreign sun.
Proxima d's magnetic field could be hundreds of times stronger than Earth's, like a powerful magnet you'd struggle to pull off a fridge.
In Stanisław Lem's novel Solaris, a planet's ocean interacts with its star — here, a real planet 'communicates' via magnetic flares.