The planet, HIP 67522 b, orbits its star in just seven days and is bombarded by radiation due to frequent energetic outbursts. These flares, nearly 100 times more energetic than predicted, are the first clear sign of a planet actively disturbing its star's magnetic field-an interaction long theorized but never observed until now.
HIP 67522, the host star, is only 17 million years old, much younger than our Sun, and is slightly larger and cooler. Its youth makes it a dynamic, magnetically charged environment. When HIP 67522 b swings by in its tight orbit, researchers suspect it disturbs the star's magnetic field, launching powerful flares at specific orbital moments.
Astronomers, led by Ekaterina Ilin at the Netherlands Institute for Radio Astronomy (ASTRON), first noticed unusual activity using NASA's TESS. To confirm their suspicions, they turned to ESA's Cheops satellite, which precisely targeted the system. Cheops detected 15 flares, most coinciding with the planet transiting the star, strongly indicating a cause-and-effect relationship.
"This is the first time we've seen a planet influence its host star," said Ekaterina. "HIP 67522 b appears to trigger particularly energetic flares when it passes in front of the star."
This interaction not only alters the star's behavior but also dooms the planet. HIP 67522 b is as large as Jupiter but far less dense-closer to the composition of candy floss. The constant radiation bombardment is eroding its atmosphere much faster than expected. If this continues, it may shrink to Neptune's size in just 100 million years.
Ekaterina's team believes the planet whips waves along the star's magnetic field lines, which then ignite flares when they hit the stellar surface. The energy of these explosions far exceeds the energy of the waves, suggesting the planet is effectively triggering stellar outbursts already primed to erupt.
The discovery overturns the longstanding assumption that stars alone govern their flaring behavior. More such star-planet systems are likely waiting to be discovered, and Ilin hopes future studies across ultraviolet and X-ray wavelengths will reveal the full extent of energy exchanges.
Maximillian Gunther, ESA's Cheops project scientist, remarked, "Cheops was designed to measure exoplanet sizes and atmospheres, not search for flares. It's amazing to see it contributing to something so unexpected."
ESA's future exoplanet mission Plato is expected to expand on these findings, with the capability to detect even subtler flares and further illuminate the dynamics of youthful star-planet interactions.
Research Report:Close-in planet induces flares on its host star
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