'Do-Nothing' Planet Actively Causes Harmful Flares From Its Parent Star

A young, energetic star has had just about enough of its clingy planet. The pair are mired in a toxic relationship, with the planet sending waves of energy toward the star—and the host star is responding with violent explosions that are destroying its planet over time.

Using the European Space Agency’s (ESA) Cheops mission, a team of astronomers from the Netherlands Institute for Radio Astronomy gathered evidence for the first known exoplanet with an apparent death wish. In a paper published Wednesday in the journal Nature, the team describes the planet, similar in size to Jupiter, which may be triggering flares of radiation from the star it orbits. Although astronomers have theorized about this type of interaction before, the flares recorded in this star system are around 100 times more energetic than expected, according to the study.

The planet, named HIP 67522 b, is one of the wispiest exoplanets ever found, with density similar to candy floss. It takes just seven days to orbit its star, which is slightly larger and cooler than the Sun. And while our host star is a middle-aged 4.5-billion-year-old, this young star has only been around for 17 million years. Compared to the Sun, this star is more energetic and has a more powerful magnetic field.

The team behind the study first spotted the young star system using TESS (Transiting Exoplanet Survey Satellite). “We hadn’t seen any systems like HIP 67522 before,” Ekaterina Ilin, lead author of the study, said in a statement. “When the planet was found it was the youngest planet known to be orbiting its host star in less than 10 days.”

The astronomers were on the hunt for stars releasing flares due to interactions with their orbiting planets, and they believed they found the perfect pair. To be sure of their findings, the team of astronomers wanted a closer look using ESA’s sensitive CHaracterising ExOPlanet Satellite (CHEOPS). “With Cheops we saw more flares, taking the total count to 15, almost all coming in our direction as the planet transited in front of the star as seen from Earth,” Ilin said.

Our own Sun releases solar flares, intense bursts of energy that explode from its atmosphere when a build-up of magnetic energy is suddenly released. Solar flares are sometimes directed toward Earth through no fault of our own. For the unlucky exoplanet, however, the strong flares from its host star are likely its own doing.

Since HIP 67522 b orbits so close to its star, it may be exerting its own magnetic influence on the host star. The planet may be gathering energy as it orbits, then redirecting that energy as waves along the star’s magnetic field line. When those waves meet the end of the magnetic field line at the star’s surface, it triggers a massive flare.

“The planet seems to be triggering particularly energetic flares,” Ilin said. “The waves it sends along the star’s magnetic field lines kick off flares at specific moments. But the energy of the flares is much higher than the energy of the waves. We think that the waves are setting off explosions that are waiting to happen.”

The radiation carried by the flares is eroding the planet’s wispy atmosphere and causing it to lose mass at a much faster rate. In the next 100 million years, HIP 67522 b could go from a Jupiter-sized planet to a much smaller Neptune-sized planet, according to the study.

The team behind the study wants to carry out follow-up observations of the unique star system using different wavelengths to find out what kind of energy is being released by the star. “I have a million questions because this is a completely new phenomenon, so the details are still not clear,” Ilin said.