Planet–comet interaction as another mechanism for formation of super-puff exoplanets

ABSTRACT This article proposes an alternative formation mechanism for super-puff exoplanets based on planet–comet interactions. Using the Graphical Sequence Model (GSM) and the Orbital Configuration Model (OCM), we demonstrate how a planet passing through a comet’s fragment chain can acquire a ‘cometary shell’, leading to extraordinarily low densities and large apparent radii characteristic of super-puffs. By applying GSM and OCM to an Earth-like planet traversing the fragment chain of a 100-km-diameter comet, this study shows that a significant number of fragments can be captured within the Roche limit. We report the orbits of the fragments and the density within the Roche limit. The fragments, breaking into dust and debris, can plausibly account for the observed radii of super-puffs. An analysis of 10 super-puffs reveals strong alignment with the hypothesis that their radii are bounded by Roche limits, further supported by 2 super-puffs near the domain of gas giants. Unlike traditional models suggesting that super-puffs formed their shells within the protoplanetary disc billions of years ago, the cometary shell hypothesis posits a significantly shorter life cycle, spanning tens to hundreds of thousands of years. This shifts our understanding of super-puff evolution and provides a practical framework for estimating their mean mass and core radius when only their apparent radius is known – a capability demonstrated for Kepler-1520b. Furthermore, the cometary shell hypothesis predicts observable phenomena such as a regular exoplanet abruptly transforming into a super-puff or vice versa, signalling the formation or collapse of a cometary shell.