Exoplanets could draw out flares from their star if they get close enough
In many of the exoplanet systems that we’ve discovered so far, the innermost planets orbit scorchingly tightly to their suns – often within only a few stellar radii. Some are so close that they’re effectively embedded within the rarefied upper atmosphere of the star itself – the corona. Such close-in planets would be expected to significantly interact with the star’s magnetic field, so much so that they could even trigger solar flares.
Ekaterina Ilin and her colleagues at the Leibniz Institute for Astrophysics Potsdam in Germany have completed the largest systematic search for just such occurrences. Flares – short-lived but intense increases in stellar brightness – are caused by the sudden release of energy from the contorted magnetic field of the star. These outbursts usually occur randomly, but the researchers reasoned that if a close-in planet is indeed magnetically interacting with its star then there ought to be a detectable pattern in the timing of flares. From our point of view, we would see a regular clustering of flares when the planet is in a particular part of its orbit.
Ilin and her team turned to the huge catalogue of data created by the Kepler and TESS (Transiting Exoplanet Survey Satellite) space telescopes. These observatories were designed to hunt for exoplanets, but their frequent, precise measurements of the changing brightnesses of large numbers of stars are also perfect for picking out flares. The researchers systematically searched these archives for signs of flares from over 1,800 stars known to have a close-in planet – representing well over half of all known exoplanetary systems. Overall, they compiled a catalogue of 1,169 individual flares in 92 planetary systems. Then they focused on the 25 stars where they’d observed at least three energetic flares, and statistically analysed their timings to see if they were bunched in phase with the innermost planet’s orbit, rather than being uniformly distributed.
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