The Dynamical History of HIP-41378 f -- Oblique Exorings Masquerading as a Puffy Planet

TL;DR

This paper proposes that HIP-41378 f is not a low-density planet but has an extensive tilted ring system caused by spin-orbit resonance and migration, explaining its observed properties and suggesting a new interpretation for super-puff planets.

Contribution

It introduces the hypothesis that HIP-41378 f hosts an oblique ring system, supported by dynamical history analysis and migration models, offering a novel explanation for super-puff characteristics.

Findings

Convergent migration explains system stability.

High obliquity tilts the ring, increasing transit depth.

Tilted rings may be common in distant super-puff planets.

Abstract

The super-puff HIP-41378 f represents a fascinating puzzle due to its anomalously low density on a far-out orbit in contrast with other known super-puffs. In this work, we explore the hypothesis that HIP-41378 f is not in fact a low-density planet, but rather hosts an opaque ring system. We analyze the dynamical history of the system, and show that convergent migration is necessary to explain the system's long-term stability. We then show that this same migration process plausibly captures HIP-41378 f into spin-orbit resonance and excites the planetary obliquity to high values. This tilts the surrounding ring and is a plausible explanation for the large transit depth. In the end, we also briefly comment on the likelihood of other super-puff planets being in high-obliquity states. We show that the existence of a tilted extensive ring around a high obliquity planet can serve as an explanation for puffy planets, particularly in multi-planetary systems at far distances from their host stars.