Revisiting migration in a disc cavity to explain the high eccentricities of warm Jupiters

TL;DR

This paper proposes that migration within a cavity in the protoplanetary disc can explain the high eccentricities of warm Jupiters, challenging the idea that planet-planet interactions are the primary cause.

Contribution

It introduces a new mechanism involving disc cavity migration to account for warm Jupiter eccentricities, supported by numerical simulations showing significant eccentricity growth.

Findings

Eccentricity can grow up to 0.4 through disc cavity migration.

The mechanism explains observed eccentricities of warm Jupiters.

Implications for disc lifetime and inner disc dispersal are discussed.

Abstract

The distribution of eccentricities of warm giant exoplanets is commonly explained through planet--planet interactions, although no physically sound argument favours the ubiquity of such interactions. No simple, generic explanation has been put forward to explain the high mean eccentricity of these planets. In this paper, we revisit a simple, plausible explanation to account for the eccentricities of warm Jupiters: migration inside a cavity in the protoplanetary disc. Such a scenario allows to excite the outer eccentric resonances, a working mechanism for higher mass planets, leading to a growth in the eccentricity while preventing other, closer resonances to damp eccentricity. We test this idea with diverse numerical simulations, which show that the eccentricity of a Jupiter-mass planet around a Sun-like star can increase up to 0.4, a value never reached before with solely planet--disc interactions. This high eccentricity is comparable to, if not larger than, the median eccentricity of warm Saturn- to Jupiter-mass exoplanets. We also discuss the effects such a mechanism would have on exoplanet observations. This scenario could have strong consequences on the discs lifetime and the physics of inner disc dispersal, which could be constrained by the eccentricity distribution of gas giants.