Sungrazer comets as analogs of star-planet magnetic interactions

¹ Université Paris-Saclay, Université Paris Cité, CEA, CNRS, AIM, 91191 Gif-sur-Yvette, France
² European Space Agency, ESTEC, Noordwijk, The Netherlands
³ Institut de Recherche en Astrophysique et Planétologie (IRAP), Université de Toulouse, CNRS, CNES, Toulouse, France
⁴ Collège Stanislas, 75006 Paris, France

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 20 March 2026
Accepted: 30 April 2026

Abstract

Context. Star–planet magnetic interactions (SPMIs) can transfer energy from an exoplanet to its host star via Alfvén waves when the planet orbits within a sub-Alfvénic stellar wind. Similar conditions were encountered by the sungrazing comet Lovejoy as it passed through the solar corona in December 2011. The possibility that comets could trigger solar activity via magnetic interactions has never been investigated.

Aims. The aim of this paper is to quantify the energetics of potential magnetic interactions between comet Lovejoy and the Sun, and to assess if enough energy could be deposited to either form a hotspot or trigger eruptions on the Sun.

Methods. We used the magnetohydrodynamic WindPredict-AW model to reconstruct the coronal magnetic field and solar wind conditions along the comet’s orbit, and determined the magnetic footpoints that connected the comet to the solar surface. By estimating the travel time of hypothetical Alfvén waves, we identified a brightening event observed by EUVI aboard STEREO-A that is spatially and temporally consistent with comet Lovejoy’s passage. We then evaluated the associated energy budget using SPMI power scaling laws.

Results. We computed the SPMI power for all magnetic field lines whose footpoints are located within 5° of the brightening. The resulting power distribution spans approximately 10¹⁴–10¹⁶ W. The power associated with the field line whose hypothetical Alfvén waves arrive just before the brightening lies at the lower end of this distribution. In comparison, the estimated radiative power of the brightening event in the STEREO-A/EUVI 195 Å channel is approximately 10¹⁷ W.

Conclusions. We find that comet Lovejoy does not generate sufficient SPMI power to be the energy source of the observed brightening intensity. However, it may still act as a perturbation to existing magnetic structures, and lead to the triggering of solar flares. Confirming this hypothesis would require additional observations that do not exist for this event, which make future passages of sungrazing comets valuable opportunities to study SPMI processes within our solar system.