Exoplanets, -moons, -comets

Updated Masses for the Gas Giants in the Eight-Planet Kepler-90 System Via Transit-Timing Variation and Radial Velocity Observations

By Keith Cowing
Status Report
astro-ph.EP
July 24, 2025
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Updated Masses for the Gas Giants in the Eight-Planet Kepler-90 System Via Transit-Timing Variation and Radial Velocity Observations
Comparison of the Kepler-90 system (gray) with our own solar system (blue). The size of each circle is proportional to the planet’s radius. Masses for the inner six Kepler-90 planets are estimated using their measured radii and an empirical mass-radius relation (Weiss & Marcy 2014). Error bars are generally too small to be seen on this scale. Lines of constant RV semi-amplitude are drawn for a solar-mass star and circular orbit to approximately illustrate the RV signal induced by each planet. astro-ph.EP

The eight-planet Kepler-90 system exhibits the greatest multiplicity of planets found to date. All eight planets are transiting and were discovered in photometry from the NASA Kepler primary mission.

The two outermost planets, g (Pg = 211 d) and h (Ph = 332 d) exhibit significant transit-timing variations (TTVs), but were only observed 6 and 3 times respectively by Kepler.

These TTVs allow for the determination of planetary masses through dynamical modeling of the pair’s gravitational interactions, but the paucity of transits allows a broad range of solutions for the masses and orbital ephemerides. To determine accurate masses and orbital parameters for planets g and h, we combined 34 radial velocities (RVs) of Kepler-90, collected over a decade, with the Kepler transit data.

We jointly modeled the transit times of the outer two planets and the RV time series, then used our two-planet model to predict their future times of transit. These predictions led us to recover a transit of Kepler-90 g with ground-based observatories in May 2024.

We then combined the 2024 transit and several previously unpublished transit times of planets g and h with the Kepler photometry and RV data to update the masses and linear ephemerides of the planets, finding masses for g and h of 15.0±1.3M⊕, and 203±16M⊕ respectively from a Markov Chain Monte Carlo analysis.

These results enable further insights into the architecturally rich Kepler-90 system and pave the way for atmospheric characterization with space-based facilities.

Distributions of masses for K90g (left) and K90h (right) from four different models: the joint RV-TTV dataset with only Kepler transits (blue), the joint RV-TTV dataset with all transits (orange), the TTV-only dataset, including post-Kepler transits (purple), and the RV-only dataset (green). The posterior mass distributions of the full RV-TTV analysis are nearly identical to those of the TTV-only analysis. The histograms are all normalized to unit area for consistent comparison. As in Fig. 7, normal distributions with mean and standard deviations taken from Table 4 are plotted over joint RV-TTV distributions in the inset for K90g. -- astro-ph.EP
Distributions of masses for K90g (left) and K90h (right) from four different models: the joint RV-TTV dataset with only Kepler transits (blue), the joint RV-TTV dataset with all transits (orange), the TTV-only dataset, including post-Kepler transits (purple), and the RV-only dataset (green). The posterior mass distributions of the full RV-TTV analysis are nearly identical to those of the TTV-only analysis. The histograms are all normalized to unit area for consistent comparison. As in Fig. 7, normal distributions with mean and standard deviations taken from Table 4 are plotted over joint RV-TTV distributions in the inset for K90g. — astro-ph.EP

David E. Shaw, Lauren M. Weiss, Eric Agol, Karen A. Collins, Khalid Barkaoui, Cristilyn N. Watkins, Richard P. Schwarz, Howard M. Relles, Chris Stockdale, John F. Kielkopf, Fabian Rodriguez Frustaglia, Allyson Bieryla, Joao Gregorio, Owen Mitchem, Katherine Linnenkohl, Adam Popowicz, Norio Narita, Akihiko Fukui, Michaël Gillon, Ramotholo Sefako, Avi Shporer, Adam Lark, Amelie Heying, Isa Khan, Beibei Chen, Kylee Carden, Donald M. Terndrup, Robert Taylor, Dasha Crocker, Sarah Ballard, Daniel C. Fabrycky

Comments: 20 pages, 13 figures, 6 tables, accepted for publication in AJ
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2507.13588 [astro-ph.EP] (or arXiv:2507.13588v1 [astro-ph.EP] for this version)

https://doi.org/10.48550/arXiv.2507.13588
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Submission history
From: David Shaw
[v1] Fri, 18 Jul 2025 00:19:08 UTC (5,738 KB)
https://arxiv.org/abs/2507.13588
Astrobiology, exoplanet,

Keith Cowing

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻

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