Stellar-planet magnetospheric interaction in the young AU Microscopii exoplanetary system

Stellar-planet magnetospheric interaction in the young AU Microscopii exoplanetary system | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Physical Sciences - Article Stellar-planet magnetospheric interaction in the young AU Microscopii exoplanetary system Riccardo Spinelli, Giancarlo Ghirlanda, Antonino Lanza, Francesco Borsa, and 11 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-8852605/v1 This work is licensed under a CC BY 4.0 License Status: Under Review Version 1 posted You are reading this latest preprint version Abstract When planets orbit close to their stars, their magnetic fields can interact releasing energy with a periodicity linked to both the planet’s orbital motion and the star’s rotation. In the Solar System, the clearest example of such interactions is the Io-Jupiter system, where the moon’s motion through Jupiter’s intense magnetic field powers strong and periodic auroral emission. For exoplanets, similar interactions are expected to occur when a planet possesses a substantial magnetic field and orbits within the sub-Alfvénic region of the stellar magnetosphere, possibly leading to periodic enhancements in stellar emission. However, despite their diagnostic power, only a few tentative detections of star-planet magnetic interactions have been reported so far. Here we show that the X-ray luminosity of the young star AU Microscopii, monitored over two years with more than eight hundred observations collected by the Einstein Probe satellite, varies by 50% of the quiescent luminosity value and shows a 4.26 sigma significance periodicity of 5.64 days. This period corresponds to half of the synodic period of the innermost planet AU Mic-b, namely the interval after which the planet returns to the longitude of one of the two magnetic poles on the stellar surface. Through the measured period and amplitude of the luminosity variation we estimate that the magnetic field of the innermost planet AU Mic b is at least B≈40-350 G, depending on whether the interconnecting magnetic loops are active intermittently or continuously throughout the synodic cycle. This result represents the first measurement of an exoplanetary magnetic field obtained through X-ray monitoring of star-planet magnetic interactions (SPMIs) and also highlights the critical role of high cadence X-ray observations in probing the magnetospheric environments of young planetary systems. The measurement of planet’s magnetic field is fundamental for assessing the long-term stability of planetary atmospheres against the stellar X--ray and Ultra Violet emission of their hosts, particularly intense in young M-dwarfs. Physical sciences/Astronomy and planetary science Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Exoplanets Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/Stars Physical sciences/Astronomy and planetary science/Astronomy and astrophysics/High-energy astrophysics Full Text Additional Declarations There is NO Competing Interest. Cite Share Download PDF Status: Under Review Version 1 posted You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-8852605","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Physical Sciences - Article","associatedPublications":[],"authors":[{"id":599865624,"identity":"a58a12fe-e2a2-498d-8b9b-19ae8c9c3c80","order_by":0,"name":"Riccardo Spinelli","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABAUlEQVRIie3RMWrDMBTG8RcMyvISrU9YuFdo8NBCDLmKvDRLKR07dHAWeckBepgOMoJkSe7QUMiUoaVLCqFUMhRCQXHHQvQfPPnHJ1sAsdh/LDl6GoBryfqzCqAA/CshZNg4cgMYNkcEPAFS4Elw5qpONm+fz+MM+Lqx9w+EQ/GqX/YK5CRApGW5mG+nOdCdsk8rd7C0rEdzFT4YJcgAjS0rwks70C3RNNifJr2DJ3zlyJcjotHi0LGStCtw64jbYtTTKZ4kLE+lmebMfwsu/E8udSoVIZoA4XbzvjPjjPO1/cDHIruol1uxU8WkXwVmfmK/7oE63m/ruO1YLBY7374BTxhFcEG6DW4AAAAASUVORK5CYII=","orcid":"https://orcid.org/0000-0001-5252-5042","institution":"Istituto Nazionale di Astrofisica","correspondingAuthor":true,"prefix":"","firstName":"Riccardo","middleName":"","lastName":"Spinelli","suffix":""},{"id":599865625,"identity":"192a4580-de2a-42e5-937a-5bcd24c93776","order_by":1,"name":"Giancarlo Ghirlanda","email":"","orcid":"https://orcid.org/0000-0001-5876-9259","institution":"INAF","correspondingAuthor":false,"prefix":"","firstName":"Giancarlo","middleName":"","lastName":"Ghirlanda","suffix":""},{"id":599865626,"identity":"1f2644d8-8d10-4f73-8785-7a6fdbc6b728","order_by":2,"name":"Antonino Lanza","email":"","orcid":"https://orcid.org/0000-0001-5928-7251","institution":"National Institute for Astrophysics (INAF)","correspondingAuthor":false,"prefix":"","firstName":"Antonino","middleName":"","lastName":"Lanza","suffix":""},{"id":599865627,"identity":"d3f61ae7-9fae-4651-86da-9b2201673956","order_by":3,"name":"Francesco Borsa","email":"","orcid":"","institution":"INAF Osservatorio Astronomico di Brera","correspondingAuthor":false,"prefix":"","firstName":"Francesco","middleName":"","lastName":"Borsa","suffix":""},{"id":599865628,"identity":"5bd63fad-31bc-4dca-bba5-048681532510","order_by":4,"name":"Ignazio Pillitteri","email":"","orcid":"","institution":"Istituto Nazionale di Astrofisica - Osservatorio Astronomico di Palermo","correspondingAuthor":false,"prefix":"","firstName":"Ignazio","middleName":"","lastName":"Pillitteri","suffix":""},{"id":599865629,"identity":"90bd9f4c-36ee-4370-a3ae-8ac0c3328280","order_by":5,"name":"Weimin Yuan","email":"","orcid":"https://orcid.org/0000-0001-8266-3024","institution":"National Astronomical Observatories of China, Chinese Academy of Sciences","correspondingAuthor":false,"prefix":"","firstName":"Weimin","middleName":"","lastName":"Yuan","suffix":""},{"id":599865630,"identity":"c80d3ef8-345e-4c5c-b062-a420c323218b","order_by":6,"name":"Z.M. 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