We all know what it’s like when Earth is on the receiving end of a solar flare. Things get spicy in the upper atmosphere, and the outbursts have the potential to disrupt technology here at home. Catastrophic flares of radiation devastate planets around other stars, too. Now it looks like scientists have found that planets orbiting close to their stars can trigger the flares that threaten to harm them.
The European Space Agency’s CHaracterising ExOPlanet Satellite (CHEOPS) mission caught a quick view of a planet called HIP 67522 b that’s stirring up strong flares in its host star. It’s a very young star – only 17 million years old – and speeds around its host star in seven days. Most of the flares it stirs up measure at least a hundred times more energetic than normal. That activity is changing the planet before our eyes.
Astronomers have long thought that a closely orbiting planet might have a flare effect on its star, but none had been discovered, according to Ekaterina Lin of the Netherlands Institute for Radio Astronomy (ASTRON). “We hadn’t seen any systems like HIP 67522 before; when the planet was found it was the youngest planet known to be orbiting its host star in less than 10 days,” she said. Lin’s team used TESS to hunt down stars that might have flares related to their planets. TESS looked at the parent star (HIP 67522) and found a likely candidate. “We quickly requested observing time with Cheops, which can target individual stars on demand, ultra-precisely,” said Lin. “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.”
Anatomy of a Flare
Flares are large eruptions of electromagnetic radiation from a star. On the Sun, flares usually take place in active regions with strong magnetic fields. They’re often associated with sunspot groups. The magnetic fields are ever-changing. They twist around like wound-up rubber bands. Eventually they become so unstable that they “break” and release electromagnetic radiation in the form of visible light, extreme ultraviolet, and X-rays. As the stored magnetic energy is released, that accelerates charged particles away from the Sun.
A large sunspot was the source of a powerful solar flare (an X9.3) and a coronal mass ejection on Sept. 6, 2017. Note: the bright vertical line and the other rays with barred lines are aberrations in our instruments caused by the bright flash of the flare. Credit: Solar Dynamics Observatory, NASA.
That outburst travels through space at the speed of light, and once it gets to Earth, it ionizes the upper atmosphere. That’s when we see auroral displays, but it’s also when communications can get disrupted. In the case of the solar flares we experience, the outbursts are caused by magnetic activity in the Sun’s surface. The same kinds of activity that cause solar flares can also result in large outbursts of charged particles called “coronal mass ejections”.
The same thing happens on other stars and their flaring activity is very much like the Sun’s. For example, Proxima Centauri (our nearest neighbor star) experiences flares, as does UV Ceti, and many other stars. There’s a whole category of them called “flare stars” that exhibit outbursty behavior similar to solar flares. In all known cases (up to now), however, it was considered a one-way street from star to planet. The new observations change that thinking.
What’s the Deal with HIP 67522 b?
The flares at HIP 67522 b are certainly very similar to our own Sun’s outbursty activity. So, how can the planet stir up flares in its host star? The science team’s observations showed that the planet’s distance from its star plays a huge role. That up-close relationship happens because the planet’s magnetic field interacts with the star’s. As HIP 67522 b whips through its short “yearly” orbit, it gathers energy and redirects it as a series of waves along the star’s magnetic field lines. When the waves get to the end of the magnetic field line on the star’s surface, it triggers a flare. The planet pays a price for this interaction, though. It’s subject to six times more radiation than it would get if it weren’t triggering flares.
As you might imagine, the intense radiation affects the planet, just as flares have an influence on Earth. All the action at HIP 67522 b is eroding the planet’s atmosphere and it’s losing mass. At the rate things are going, according to Lin, this world could go from its current existence as an almost-Jupiter-size world to one about the size of Neptune.
Flares inflicted on the host star by the magnetic interaction with the exoplanet are slowly eroding away the planet’s atmosphere. Credit: Janine Fohlmeister (Leibniz Institute for Astrophysics Potsdam)
The host star HIP 67522 is a G-type main sequence star similar to the Sun. It lies about 400 light-years away and it has two planets. HIP 67522 b was the youngest “close-in” planet at its discovery. Since then astronomers have found others. The observations of the planet-caused flaring is a new wrinkle in understanding these worlds, according to Lin, who wants to have her team study more of them to understand the mechanism of flaring. “There are two things that I think are most important to do now. The first is to follow up in different wavelengths (CHEOPS covers visible to near-infrared wavelengths) to find out what kind of energy is being released in these flares – for example ultraviolet and X-rays are especially bad news for the exoplanet,” she said. “The second is to find and study other similar star-planet systems; by moving from a single case to a group of 10–100 systems, theoretical astronomers will have something to work with.”
For More Information
Clingy Planets Can Trigger Own Doom, Suspect CHEOPS and TESS
https://www.esa.int/Science_Exploration/Space_Science/Cheops/Clingy_planets_can_trigger_own_doom_suspect_Cheops_and_TESS (ESA)
Searching for Planet-induced Radio Signals from the Young Close-in Planet Host Star HIP 67522
https://www.aanda.org/articles/aa/full_html/2025/07/aa54684-25/aa54684-25.html