Discriminate between migration histories for TOI-2158 b

Determine whether the present-day architecture of the TOI-2158 system reflects high-eccentricity tidal migration of TOI-2158 b or an alternative history involving protoplanetary-disc migration followed by subsequent excitation of the outer planets.

Background

TOI-2158 b is nearly circular and accompanied by the eccentric outer planet TOI-2158 c and a possible additional distant companion. This architecture is compatible with high-eccentricity tidal migration, in which outer companions excite the inner planet’s eccentricity before tidal dissipation shrinks and circularizes its orbit.

However, the observed system architecture does not uniquely identify that pathway. The authors explicitly note that migration through the protoplanetary disc followed by later dynamical excitation of the outer planets remains viable, leaving the origin of TOI-2158 b unresolved.

References

However, the present-day architecture does not uniquely establish such a history, and alternative scenarios, such as migration through the protoplanetary disc followed by subsequent excitation of the outer planets, cannot be ruled out.

— TS23/McDonald and FIES/NOT strike again. Two new warm Jupiter systems and outer companions in a third  (2609.30915 - Knudstrup et al., 25 Sep 2026) in Section 4.2, subsection “Formation and migration”