Toddlers in Resonance I: low masses and eccentricities of the 17 Myr giant planets HIP 67522 bc from transit timing variations

@misc{james2026toddlers,
  title = {{Toddlers in Resonance I: low masses and eccentricities of the 17 Myr giant planets HIP 67522 bc from transit timing variations}},
  author = {Hannah R. James and Madyson G. Barber and Andrew W. Mann and Pa Chia Thao and Adam L. Kraus and Benjamin M. Tofflemire and Andrew Vanderburg and Lyu Abe and Tristan Guillot and Olga Suarez and Djamel Mekarnia and Amaury H. M. J. Triaud and Vincent Deloupy and Mayuko Mori and Jerome P. de Leon and Norio Narita and Akihiko Fukui and John H. Livingston and George Zhou and Camille M. L. Guenée and Juliette Becker and Ana Isabel Lopez Murillo and Karen A. Collins and Richard P. Schwarz and Chris Stockdale and Thiam-Guan Tan and Keith Horne and Leah J. Boff and Mackenna L. Wood and Nidia Morrell and Luke G. Bouma},
  howpublished = {arXiv},
  year = {2026},
  month = sep,
  doi = {10.48550/arxiv.2609.35979},
  eprint = {2609.35979},
  archivePrefix = {arXiv},
  url = {https://arxiv.org/abs/2609.35979},
  note = {CC BY 4.0},
}

TY  - UNPB
TI  - Toddlers in Resonance I: low masses and eccentricities of the 17 Myr giant planets HIP 67522 bc from transit timing variations
AU  - Hannah R. James
AU  - Madyson G. Barber
AU  - Andrew W. Mann
AU  - Pa Chia Thao
AU  - Adam L. Kraus
AU  - Benjamin M. Tofflemire
AU  - Andrew Vanderburg
AU  - Lyu Abe
AU  - Tristan Guillot
AU  - Olga Suarez
AU  - Djamel Mekarnia
AU  - Amaury H. M. J. Triaud
AU  - Vincent Deloupy
AU  - Mayuko Mori
AU  - Jerome P. de Leon
AU  - Norio Narita
AU  - Akihiko Fukui
AU  - John H. Livingston
AU  - George Zhou
AU  - Camille M. L. Guenée
AU  - Juliette Becker
AU  - Ana Isabel Lopez Murillo
AU  - Karen A. Collins
AU  - Richard P. Schwarz
AU  - Chris Stockdale
AU  - Thiam-Guan Tan
AU  - Keith Horne
AU  - Leah J. Boff
AU  - Mackenna L. Wood
AU  - Nidia Morrell
AU  - Luke G. Bouma
PY  - 2026
DA  - 2026/09/28
PB  - arXiv
DO  - 10.48550/arxiv.2609.35979
UR  - https://arxiv.org/abs/2609.35979
AB  - Infant (<100\,Myr) transiting planet systems provide glimpses into the processes that shape the observed mature planet population. Masses for these planets are powerful data points for testing theories of planet formation and evolution. Because young systems tend to be in mean-motion resonances (MMR) and show higher rates of transit timing variations (TTVs), we can take advantage of deviations in the expected versus observed transit timings due to gravitational interactions between the planets to determine the planetary masses and orbital eccentricities. Here we report the TTV analysis of HIP\,67522, a 17\,Myr two-planet system near a 2:1 orbital resonance. The analysis is based on 55 transit observations (50 epochs) of planet b and 29 transit observations (22 epochs) of planet c, taken across 11 facilities. Assuming circular orbits, we determine masses of M_b=25.0^+7.6_−7.8M_⊕ and M_c=11.2±1.4M_⊕. Allowing for eccentric orbits, we find M_b=23.1^+15.4_−12.4M_⊕ and M_c=11.8^+3.0_−2.3M_⊕, and low eccentricities (<0.1) for both planets. Adopting a Gaussian prior on M_b from the JWST transmission spectrum tightens the eccentric-solution mass for planet c to 9.7^+1.9_−1.6M_⊕, which is our recommended solution. The low masses and large radii are consistent with a contracting atmosphere planet formation model, such as Gas Dwarf formation. Given the challenge of radial-velocity masses and the high rate of TTVs seen in young systems, TTV-masses will be essential for testing theories of the formation and evolution of super-Earths and sub-Neptunes and determining the conditions that create the most common types of planets in the Galaxy.
ER  -