Evidence for LP 890-9d via Transit Timing Variations

Kevin B. Stevenson; Guangwei Fu; Kristin S. Sotzen; E. M. May; Larissa Palethorpe; Jacob Lustig-Yaeger; Ted M. Johnson; Eric Agol; Katherine A. Bennett; Carlos Gascón; David K. Sing; Jeff A. Valenti; Hannah R. Wakeford

arXiv · 2609.05312

Evidence for LP 890-9d via Transit Timing Variations

Kevin B. Stevenson·Guangwei Fu·Kristin S. Sotzen·E. M. May·Larissa Palethorpe·Jacob Lustig-Yaeger·Ted M. Johnson·Eric Agol·Katherine A. Bennett·Carlos Gascón·David K. Sing·Jeff A. Valenti·Hannah R. Wakeford

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Abstract

LP 890-9, also known as SPECULOOS-2 and TOI-4306, is a nearby late-M dwarf hosting two confirmed transiting rocky exoplanets. We analyze 20 JWST/NIRSpec PRISM transits of LP 890-9b and LP 890-9c obtained as part of GO program 7073 and detect statistically significant transit timing variations (TTVs), with peak-to-peak amplitudes of ~17 s and ~35 s, respectively. Using analytic linear TTV theory, we find that the known two-planet configuration cannot reproduce the measured TTV amplitudes or super-period, whereas three-planet models provide substantially better fits. The best-fit configuration places the candidate third planet, LP 890-9d, between planets b and c, with an orbital period of ~4.4 days; however, the current data do not uniquely determine its orbital architecture, and periods spanning 4.0-6.9 days remain plausible. TESS is insensitive to transits of LP 890-9d and we find no evidence for the candidate in JWST observations, although the phase coverage (ranging from ~50% to ~80%) depends strongly on the candidate orbital period. Additional high-precision transit observations of LP 890-9b and LP 890-9c are needed to refine their TTV solutions and further constrain the orbital properties of the third planet.

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Kevin B. Stevenson, Guangwei Fu, Kristin S. Sotzen, E. M. May, Larissa Palethorpe, Jacob Lustig-Yaeger, Ted M. Johnson, Eric Agol, Katherine A. Bennett, Carlos Gascón, David K. Sing, Jeff A. Valenti, Hannah R. Wakeford. 2026-09-04. Evidence for LP 890-9d via Transit Timing Variations. https://arxiv.org/abs/2609.05312

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