Determine the orbital architecture of LP 890-9d

Determine the orbital architecture of the candidate third planet LP 890-9d in the LP 890-9 system, including which of the plausible orbital periods spanning approximately 4.0–6.9 days is favored by additional observations.

Background

Transit-timing variations measured for the confirmed planets LP 890-9b and LP 890-9c favor a three-planet interpretation over the known two-planet model. The preferred dynamical configuration places the candidate LP 890-9d between planets b and c, but the observed timing data admit multiple interior orbital-period solutions.

The existing JWST observations do not detect a transit of LP 890-9d, and the candidate's orbital period, inclination, and phase remain insufficiently constrained. Additional high-precision transit-timing and transit-search observations are therefore required to distinguish among the plausible orbital architectures.

References

The best-fit configuration places the candidate third planet, LP 890-9d, between planets b and c, with Pd ∼ 4.4 days; however, the current data do not uniquely determine its orbital architecture and periods spanning 4.0–6.9 days remain plausible.

— Evidence for LP 890-9d via Transit Timing Variations  (2609.05312 - Stevenson et al., 4 Sep 2026) in Abstract; Section 4, Discussion, p. 12

The current LP 890-9b timings do not show a clear anti-correlation with the LP 890-9c TTVs, which further disfavors the two-planet interpretation; however, the planet-b baseline spans only 43 days (40% of the inferred super-period), so the present data cannot definitively establish whether or not such an anti-correlation is present.

— Evidence for LP 890-9d via Transit Timing Variations  (2609.05312 - Stevenson et al., 4 Sep 2026) in Section 3.1, p. 10; Section 4, Discussion, p. 12