A gas giant orbiting in remote space has created a stir: After persistent prodding, its volatile star seeks retaliation, and the planet will endure the aftermath, as reported by astronomers.
The exoplanet HIP 67522 b, swollen to the dimensions of Jupiter, revolves so closely to its star that it instigates violent flares—explosive bursts of high-energy radiation—from its host that then impact it. These flares gradually erode the planet’s fragile atmosphere.
Scientists utilizing the Characterising Exoplanet Satellite (Cheops) mission—managed by NASA’s European counterpart—recorded 15 significant eruptions from the star HIP 67522, most occurring when the planet transited in front of it. This occurrence isn’t incidental, according to the European Space Agency. The team theorizes that the planet is disrupting the star’s magnetic field, initiating explosions far more potent than any solar flares directed at Earth.
This marks the first occasion where researchers have witnessed a planet seemingly provoking its star. Previously, it was believed that energy flowed unidirectionally from stars to their planets: the star emits, the planet absorbs. However, HIP 67522 b is altering that story, inciting flares that retaliate.
“Cheops was intended to characterize the dimensions and atmospheres of exoplanets, rather than search for flares,” stated Maximilian Günther, the mission’s project scientist. “It’s truly fascinating to see the mission contributing to this and other results that extend far beyond its original purpose.”
Located about 400 light-years away, the star HIP 67522 is youthful—only 17 million years old—and tempestuous. It’s marginally larger and cooler than the sun but possesses more energy, rotating swiftly.
HIP 67522 b orbits at an astonishing velocity, finishing a revolution in merely seven days. This proximity creates strain. As the exoplanet moves around its host, it appears to inject energy into the star’s magnetic field, akin to a whip cracking. When the wave reaches the surface, the star responds with even greater intensity.
HIP 67522 b is already among the least dense exoplanets ever discovered, with a composition resembling cotton candy more than a solid. Its atmosphere is swiftly eroding under the star’s rapid flares. The researchers estimate the planet receives six times the radiation it would otherwise endure. Their findings are published in the journal Nature.
“The waves it transmits along the star’s magnetic field lines trigger flares at certain intervals. Yet, the energy of the flares is significantly greater than the energy of the waves,” remarked Ekaterina Ilin from the Netherlands Institute for Radio Astronomy, who led the study. “We believe the waves are igniting explosions that have been primed to occur.”
The notion that a planet might instigate its own demise isn’t novel. This theory has been proposed since the 1990s, but this is the first solid proof. The discovery provokes further inquiries: How many planets are ensnared in this type of feedback loop? What types of flares are they generating? And how rapidly are the planets’ atmospheres dissipating?
In a cosmic blink—perhaps 100 million years—HIP 67522 b could diminish to the size of Neptune or smaller.
Astronomers are now eager to broaden the investigation. Using tools like NASA’s Transiting Exoplanet Survey Satellite (TESS) and the forthcoming ESA Plato mission, scientists aim to uncover more of these doomed planets and ascertain whether HIP 67522 b is an anomaly or simply one among many unfortunate worlds courting danger.