Kinematic ages of ultra-short-period planet hosts

Determine whether ultra-short-period planet hosts are systematically older than the general population of planetary hosts, accounting for the sensitivity of the inferred age comparison to the thin-disk selection criterion and other differences in host-star properties.

Background

The paper compares the vertical velocity dispersion of ultra-short-period planet (USP) hosts with that of the overall sample of Kepler planetary hosts, using stellar kinematics as an age proxy. The comparison is complicated because a larger fraction of USP hosts may belong to the thick disk, and because the inferred dispersion difference changes depending on how probable thick-disk contaminants are removed. With no thick-disk cut or a less stringent cut, the dispersions are statistically indistinguishable; a strict thin-disk selection produces only a marginal difference of approximately 2σ.

The authors therefore leave unresolved whether USP hosts are systematically older than general planetary hosts and note that a more systematic analysis is needed, including correction for other differences in USP host properties such as stellar type.

References

As the result is sensitive to the selection criterion of thin disk stars, it is unclear whether the ages of the USP hosts are indeed systematically older than the general planetary hosts.

— Are Near Resonant Multiple-planet Systems from Kepler Young?  (2608.12786 - Zhu et al., 13 Aug 2026) in Appendix, Section “On the kinematic ages of USP hosts” (Section sec:usp)