Exoplanets & Exomoons

Characterisation Of The TOI-421 Planetary System Using CHEOPS, TESS, and Archival Radial Velocity Data

By Keith Cowing
Status Report
April 20, 2024
Filed under , , , , , , , , ,
Characterisation Of The TOI-421 Planetary System Using CHEOPS, TESS, and Archival Radial Velocity Data
Stability analysis of the TOI-421 planetary system. For fixed initial conditions (Table 6), the parameter space of the system was explored by varying the orbital period Pb and the eccentricity eb of planet-b (left panel) and the eccentricities of both planets (right panel). The step size was 10−3 day in orbital period and 0.0025 in eccentricity. For each initial condition, the system was integrated over 5000 yr and a stability indicator was calculated, which involved a frequency analysis of the mean longitude of the inner planet. The chaotic diffusion was measured by the variation in the frequency (see text). Red points correspond to highly unstable orbits, while blue points correspond to orbits which are likely to be stable on a billion-years timescale. The black dots show the values of the best fit solution (Table 6). — astro-ph.EP

The TOI-421 planetary system contains two sub-Neptune-type planets and is a prime target to study the formation and evolution of planets and their atmospheres.

The inner planet is especially interesting as the existence of a hydrogen-dominated atmosphere at its orbital separation cannot be explained by current formation models without previous orbital migration. We jointly analysed photometric data of three TESS sectors and six CHEOPS visits as well as 156 radial velocity data points to retrieve improved planetary parameters.

We also searched for TTVs and modelled the interior structure of the planets. Finally, we simulated the evolution of the primordial H-He atmospheres of the planets using two different modelling frameworks. We determine the planetary radii and masses of TOI-421 b and c to be Rb=2.64±0.08R, Mb=6.7±0.6M, Rc=5.09±0.07R, and Mc=14.1±1.4M.

We do not detect any statistically significant TTV signals. Assuming the presence of a hydrogen-dominated atmosphere, the interior structure modelling results in both planets having extensive envelopes. While the modelling of the atmospheric evolution predicts for TOI-421 b to have lost any primordial atmosphere that it could have accreted at its current orbital position, TOI-421 c could have started out with an initial atmospheric mass fraction somewhere between 10 and 35%.

We conclude that the low observed mean density of TOI-421 b can only be explained by either a bias in the measured planetary parameters (e.g. driven by high-altitude clouds) and/or in the context of orbital migration. We also find that the results of atmospheric evolution models are strongly dependent on the employed planetary structure model.

A. F. Krenn, D. Kubyshkina, L. Fossati, J. A. Egger, A. Bonfanti, A. Deline, D. Ehrenreich, M. Beck, W. Benz, J. Cabrera, T. G. Wilson, A. Leleu, S. G. Sousa, V. Adibekyan, A. C. M. Correira, Y. Alibert, L. Delrez, M. Lendl, J. A. Patel, J. Venturini, R. Alonso, G. Anglada, J. Asquier, T. Bárczy, D. Barrado Navascues, S. C. C. Barros, W. Baumjohann, T. Beck, N. Billot, X. Bonfils, L. Borsato, A. Brandeker, C. Broeg, S. Charnoz, A. Collier Cameron, Sz. Csizmadia, P. E. Cubillos, M. B. Davies, M. Deleuil, O. D. S. Demangeon, B.-O. Demory, A. Erikson, A. Fortier, M. Fridlund, D. Gandolfi, M. Gillon, M. Güdel, M. N. Günther, J. Hasiba, A. Heitzmann, C. Helling, S. Hoyer, K. G. Isaak, L. L. Kiss, K. W. F. Lam, J. Laskar, A. Lecavelier des Etangs, C. Lovis, D. Magrin, P. F. L. Maxted, C. Mordasini, V. Nascimbeni, G. Olofsson, R. Ottensamer, I. Pagano, E. Pallé, G. Peter, G. Piotto, D. Pollacco, D. Queloz, R. Ragazzoni, N. Rando, H. Rauer, I. Ribas, M. Rieder, N. C. Santos, G. Scandariato, D. Ségransan, A. E. Simon, A. M. S. Smith, M. Stalport, M. Steller, Gy. M. Szabó, N. Thomas, S. Udry, B. Ulmer, V. Van Grootel, E. Villaver, V. Viotto, N. A. Walton, T. Zingales

Comments: 21 pages, 12 figures, accepted for publication in A&A
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2404.11074 [astro-ph.EP] (or arXiv:2404.11074v1 [astro-ph.EP] for this version)
Submission history
From: Andreas Krenn
[v1] Wed, 17 Apr 2024 05:14:19 UTC (7,037 KB)


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) 🖖🏻