Abstract
In the past decade, hundreds of exoplanets have been discovered in extremely short orbits below 10 days. Unlike in the Solar System, planets in these systems orbit their host stars close enough to disturb the stellar magnetic field lines1. The interaction can enhance the magnetic activity of the star, such as its chromospheric2 and radio3 emission or flaring4. So far, the search for magnetic star–planet interactions has remained inconclusive. Here we report the detection of planet-induced flares on HIP 67522, a 17 million-year-old G dwarf star with two known close-in planets5,6. Combining space-borne photometry from the Transiting Exoplanet Survey Satellite and dedicated Characterising Exoplanets Telescope observations over 5 years, we find that the 15 flares in HIP 67522 cluster near the transit phase of the innermost planet, indicating persistent magnetic star–planet interaction in the system. The stability of interaction implies that the innermost planet is continuously self-inflicting a six times higher flare rate than it would experience without interaction. The subsequent flux of energetic radiation and particles bombarding HIP 67522 b may explain the remarkably extended atmosphere of the planet, recently detected with the James Webb Space Telescope7. HIP 67522 is, therefore, an archetype to understand the impact of magnetic star–planet interaction on the atmospheres of nascent exoplanets.
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Data availability
This paper includes data collected by the TESS mission, which are publicly available from the Mikulski Archive for Space Telescopes under ObsID TIC 166527623. CHEOPS data analysed in this article will be made available in the CHEOPS mission archive (https://cheops.unige.ch/archive_browser/). PIPE-reduced and de-trended CHEOPS light curves are available on Zenodo51 (https://doi.org/10.5281/zenodo.15195056).
Code availability
All codes necessary to reproduce the results in this paper are available on GitHub (https://github.com/ekaterinailin/hip67522-spi/tree/flaring-spi).
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Acknowledgements
We thank J. Alvarado-Gómez for the discussions regarding CME-driven mass loss. E.I. and H.K.V. acknowledge funding from the European Research Council under the Horizon Europe programme of the European Union (grant no. 101042416 STORMCHASER). K.P. acknowledges funding from the German Leibniz-Gemeinschaft under project no. P67/2018. S.B. acknowledges funding from the Dutch research council (NWO) under the talent programme (Vidi grant VI.Vidi.203.093). A.B. was supported by the SNSA. H.C. acknowledges the support of the Swiss National Science Foundation under grant no. PCEFP2_194576. Funding for the TESS mission was provided by the Science Mission Directorate of NASA. CHEOPS is an ESA mission in partnership with Switzerland with important contributions to the payload and the ground segment from Austria, Belgium, France, Germany, Hungary, Italy, Portugal, Spain, Sweden and the UK. The CHEOPS Consortium thanks the support received from all the agencies, offices, universities and industries involved; their flexibility and willingness to explore new approaches were essential to the success of this mission.
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E.I. and K.P. initiated the star–planet interaction search project. E.I. led the processing of TESS and CHEOPS data with input from A.B., led the energetics and geometric calculations with input from H.K.V. and K.P.; E.I. and H.K.V. performed the clustering analysis with input from J.R.C. and S.B.; S.B. provided input on the stellar wind estimate. H.C. aided with the data collection and sharing across projects. All authors commented on the paper.
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Extended data figures and tables
Extended Data Fig. 1 TESS light curves of HIP 67522.
Blue scatter shows the 2-min TESS PDC_SAP flux. Light blue shades show the batman36 transit models of HIP 67522 b. Orange vertical lines mark the detected flares, and grey hatched area mark the best-fit window of elevated flare rate.
Extended Data Fig. 2 Flares in TESS light curves of HIP 67522.
Yellow lines show the polynomial fit including the batman36 transit model of HIP 67522 b, highlighted with a blue shade. Each bottom panel shows the residual light curve with the polynomial model and transit removed. The flare template was fit within the orange highlighted region.
Extended Data Fig. 3 CHEOPS light curves of HIP 67522.
Top panels show the PIPE reduced 10-s cadence imagette light curves as blue scatter. Yellow lines show the polynomial fit including the batman36 transit model of HIP 67522 b, highlighted with a blue shade. Each bottom panel highlights flares within the orange shaded regions, which are reintroduced into the residual light curve (blue scatter).
Extended Data Fig. 4 Bayes Factor and Akaike Information Criterion.
The values for both statistics converge above 75 orbital phase bins, indicating that the phases are sufficiently resolved.
Extended Data Fig. 5 Planet-induced emission power.
Estimate of planet-induced power (overlapping blue solid lines) as a function of highest possible induced flare energy \({E}_{\max }\). Lower lines indicate a smaller lower limit for the energy of planet-induced flares in the range 1032 − 1033 erg. Below this limit, flares cannot be distinguished from X-ray quiescent emission28. The flares on HIP 67522 are distributed following a power law distribution with slope <2, so that the total power integrated over the distribution is determined by the high energy tail of the distribution, i.e., by \({E}_{\max }\). The measured power is incompatible with the power expected from the Alfvén wing star-planet interaction mechanism1 (blue shade), and must therefore tap into a different energy source, e.g., the energy stored in pre-flare coronal loops. The X-ray quiescent emission indicates an estimate of the energy budget available to the interaction (dotted line).
Extended Data Fig. 6 CME-induced mass loss rate.
Estimate of mass loss rate from HIP 67522 b due to CMEs as a function of opening angle and efficiency η, assuming all CMEs intercept the planet’s ___location. The shaded region marks the range of typical opening angles of solar CMEs34. The orange line highlights the assumed efficiency factor of η = 0.1, and the black dashed line indicates a 100% increase in mass loss rate compared to XUV-driven mass loss only.
Extended Data Fig. 7 Flare rates of stars similar to HIP 67522.
Flare frequency distributions of G dwarf stars with rotation periods 0.27 − 5.41 d, and effective temperatures 5113 − 5916 K with at least three flares observed with TESS44, excluding known eclipsing binaries from52. We set the upper limit on the flare rates λ0 and λ1 conservatively to 2 d−1 (horizontal dashed line) above the minimum flare energy in the sample (vertical dashed line). Note that the44 sample still likely contains binary stars, such that the true flare rate of some stars is lower than shown.
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Ilin, E., Vedantham, H.K., Poppenhäger, K. et al. Close-in planet induces flares on its host star. Nature (2025). https://doi.org/10.1038/s41586-025-09236-z
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DOI: https://doi.org/10.1038/s41586-025-09236-z
