Scientists have discovered the first clear case of a planet causing its host star to flare, offering new insights into the dramatic interactions between stars and their closely orbiting planets. The research was led by Dr. Ekaterina Ilin and Dr. Harish K. Vedantham of ASTRON (Netherlands Institute for Radio Astronomy), as well as Prof. Dr. Katja Popppenhäger from AIP, along with an international team of collaborators.

The study focused a young star system HIP 67522, which is located around 408 light years away in the constellation of Upper Centaurus Lupus. In one of the closest known orbits, a giant planet passes its star in less than seven days. The team led by Ekaterina Ilin has discovered that stellar flares frequently erupt at the moments when the planet passes in front of the star from our perspective. These huge eruptions of electromagnetic energy and flares seem to be triggered directly by the planet's influence.

"We've found the first clear evidence of flaring star-planet interaction, where a planet triggers energetic eruptions on its host star," said Ekaterina Ilin. "What's particularly exciting is that this interaction has persisted for at least three years, allowing us to study it in detail."

The analysis is based on five years of data from NASA's TESS satellite and the European Space Agency's CHEOPS telescope. In their study, the astronomers show that the planet releases energy by disturbing the magnetic field lines of its star, which discharges explosively - a veritable ‘firework display’ in space. "This type of star-planet interaction has been expected for a long time, but getting the observational evidence was only possible with this large space telescope dataset", said Katja Poppenhäger.

This interplanetary interaction also has dramatic effects on the planet itself: The findings show that the planet induces the star to flare approximately six times more often than it would have without the interaction. Data from the James Webb Space Telescope shows a unusually expanded atmosphere - a possible result of the intense bursts of radiation. "The planet is essentially subjecting itself to an intense bombardment of radiation and particles from these induced flares," explained Harish K. Vedantham, co-author and researcher at ASTRON. "This self-inflicted space weather likely causes the planet's atmosphere to puff up and may dramatically accelerate the rate at which the planet is losing its atmosphere."

This discovery establishes HIP 67522 as an archetypal system for studying how magnetic interactions between stars and planets can affect planetary evolution, particularly for young planets. The team plans further observations of this and other systems to better understand how energy is transported and released along the planet-star connection, how common this phenomenon is among young planetary systems and what it means for the ability of young planets to retain their nascent atmospheres.