TESS Spots a Super-puff: The Remarkably Low Density of TOI-1420b

Creators: Yoshida, Stephanie¹; Vissapragada, Shreyas¹; Latham, David W.¹; Bieryla, Allyson¹; Thorngren, Daniel P.²; Eastman, Jason D.¹; López-Morales, Mercedes¹; Barkaoui, Khalid^{3, 4, 5}; Beichman, Charles^{6, 7}; Berlind, Perry¹; Buchave, Lars A.⁸; Calkins, Michael L.¹; Ciardi, David R.^{6, 7}; Collins, Karen A.¹; Cosentino, Rosario⁹; Crossfield, Ian J. M.¹⁰; Dai, Fei⁷; DiTomasso, Victoria¹; Dowling, Nicholas¹¹; Esquerdo, Gilbert A.¹; Forés-Toribio, Raquel¹²; Ghedina, Adriano⁹; Goliguzova, Maria V.¹³; Golub, Eli¹⁴; Gonzales, Erica J.¹⁵; Horta, Ferran Grau¹⁶; Higuera, Jesus¹⁴; Hoch, Nora¹⁷; Horne, Keith¹⁸; Howell, Steve B.¹⁹; Jenkins, Jon M.¹⁹; Klusmeyer, Jessica¹⁴; Laloum, Didier²⁰; Lissauer, Jack J.¹⁹; Logsdon, Sarah E.¹⁴; Malavolta, Luca²¹; Matson, Rachel A.²²; Matthews, Elisabeth C.²³; McLeod, Kim K.¹⁷; Medina, Jennifer V.²⁴; Muñoz, Jose A.¹²; Osborn, Hugh P.^{4, 25}; Safonov, Boris¹³; Schlieder, Joshua²⁶; Schmidt, Michael¹¹; Schweiker, Heidi¹⁴; Seager, Sara⁴; Sozzetti, Alessandro²⁷; Srdoc, Gregor²⁸; Stefánsson, Guđmundur²⁹; Strakhov, Ivan A.¹³; Striegel, Stephanie^{19, 30}; Villaseñor, Joel⁴; Winn, Joshua N.²⁹

1. Harvard-Smithsonian Center for Astrophysics
2. Johns Hopkins University
3. University of Liège
4. Massachusetts Institute of Technology
5. Instituto de Astrofísica de Canarias
6. Infrared Processing and Analysis Center
7. California Institute of Technology
8. Technical University of Denmark
9. Telescopio Nazionale Galileo
10. University of Kansas
11. Ludwig-Maximilians-Universität München
12. University of Valencia
13. Lomonosov Moscow State University
14. NOIRLab
15. University of California, Santa Cruz
16. Observatori de Ca l'Ou, Carrer de dalt 18, Sant Martí Sesgueioles E-08282, Barcelona, Spain
17. Wellesley College
18. University of St Andrews
19. Ames Research Center
20. Société Astronomique de France, 3 Rue Beethoven, F-75016 Paris, France
21. University of Padua
22. United States Naval Observatory
23. Max Planck Institute for Astronomy
24. Space Telescope Science Institute
25. University of Bern
26. Goddard Space Flight Center
27. INAF Osservatorio Astrofisico di Torino
28. Kotizarovci Observatory, Sarsoni 90, 51216 Viskovo, Croatia
29. Princeton University
30. Search for Extraterrestrial Intelligence

Abstract

We present the discovery of TOI-1420b, an exceptionally low-density (ρ = 0.08 ± 0.02 g cm⁻³) transiting planet in a P = 6.96 days orbit around a late G-dwarf star. Using transit observations from TESS, LCOGT, Observatoire Privé du Mont, Whitin, Wendelstein, OAUV, Ca l'Ou, and KeplerCam, along with radial velocity observations from HARPS-N and NEID, we find that the planet has a radius of R_p = 11.9 ± 0.3R_⊕ and a mass of M_p = 25.1 ± 3.8M_⊕. TOI-1420b is the largest known planet with a mass less than 50M_⊕, indicating that it contains a sizeable envelope of hydrogen and helium. We determine TOI-1420b's envelope mass fraction to be f_(env) = 82₋₆⁺⁷%, suggesting that runaway gas accretion occurred when its core was at most four to five times the mass of the Earth. TOI-1420b is similar to the planet WASP-107b in mass, radius, density, and orbital period, so a comparison of these two systems may help reveal the origins of close-in low-density planets. With an atmospheric scale height of 1950 km, a transmission spectroscopy metric of 580, and a predicted Rossiter–McLaughlin amplitude of about 17 m s⁻¹, TOI-1420b is an excellent target for future atmospheric and dynamical characterization.

Copyright and License

Original content from this work may be used under the terms of the Creative Commons Attribution 4.0 licence. Any further distribution of this work must maintain attribution to the author(s) and the title of the work, journal citation and DOI.

Acknowledgement

We thank the referee for detailed comments that improved the quality of this manuscript, and we thank Andrew Vanderburg for helpful discussions regarding the TESS data. The postdoctoral fellowship of K.B. is funded by F.R.S.-FNRS grant T.0109.20 and by the Francqui Foundation. K.A.C. acknowledges support from the TESS mission via subaward s3449 from MIT. K.K.M. acknowledges support from the New York Community Trust Fund for Astrophysical Research. N.H. was supported by a NASA Massachusetts Space Grant fellowship. M.V.G. and I.A.S. acknowledge the support of the Ministry of Science and Higher Education of the Russian Federation under the grant 075-15-2020-780 (N13.1902.21.0039). G.S. acknowledges support provided by NASA through the NASA Hubble Fellowship grant HST-HF2-51519.001-A awarded by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS5-26555.

We acknowledge the use of public TESS data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center. Resources supporting this work were provided by the NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center for the production of the SPOC data products. This paper includes data collected by the TESS mission, which are publicly available from the Mikulski Archive for Space Telescopes (MAST) operated by the Space Telescope Science Institute (STScI). Funding for the TESS mission is provided by NASA's Science Mission Directorate. The specific observations analyzed can be accessed via doi:10.17909/har4-7y03.

This work makes use of observations from the LCOGT network. Part of the LCOGT telescope time was granted by NOIRLab through the Mid-Scale Innovations Program (MSIP). MSIP is funded by NSF. This research has made use of the Exoplanet Follow-up Observation Program (ExoFOP; doi:10.26134/ExoFOP5) website, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. Funding for the TESS mission is provided by NASA's Science Mission Directorate. This paper contains data taken with the NEID instrument, which was funded by the NASA-NSF Exoplanet Observational Research (NN-EXPLORE) partnership and built by Pennsylvania State University. NEID is installed on the WIYN telescope, which is operated by the National Optical Astronomy Observatory, and the NEID archive is operated by the NASA Exoplanet Science Institute at the California Institute of Technology. NN-EXPLORE is managed by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration. Data presented herein were obtained at the WIYN Observatory, or the CTIO SMARTS 1.5 m, or MINERVA-Australis from telescope time allocated to NN-EXPLORE through the scientific partnership of the National Aeronautics and Space Administration, the National Science Foundation, and the NOIRLab. The authors are honored to be permitted to conduct astronomical research on Iolkam Du'ag (Kitt Peak), a mountain with particular significance to the Tohono O'odham. This work has made use of data from the European Space Agency (ESA) mission Gaia (https://www.cosmos.esa.int/gaia), processed by the Gaia Data Processing and Analysis Consortium (DPAC; https://www.cosmos.esa.int/web/gaia/dpac/consortium). Funding for the DPAC has been provided by national institutions, in particular the institutions participating in the Gaia Multilateral Agreement. This research made use of exoplanet (Foreman-Mackey et al. 2021a, 2021b) and its dependencies (Astropy Collaboration et al. 2013, 2018; Kipping 2013; Salvatier et al. 2016; Theano Development Team 2016; Kumar et al. 2019; Luger et al. 2019; Agol et al. 2020).

Facilities

Exoplanet Archive - , ExoFOP - , TESS - , TNG (HARPS-N) - Telescopio Nazionale Galileo, WIYN (NEID) - Wisconsin-Indiana-Yale-NOAO Telescope, LCOGT - Las Cumbres Observatory Global Telescope, FLWO: 1.2 m (KeplerCam) - Fred Lawrence Whipple Observatory's 1.2 meter Telescope, WCWO: 0.6 m - , Gemini: Gillett (NIRI) - Gillett Gemini North Telescope.

Software References

AstroImageJ (Collins et al. 2017), TAPIR (Jensen 2013), EXOFASTv2 (Eastman et al. 2019), exoplanet (Foreman-Mackey et al. 2021a), pymc3 (Salvatier et al. 2016), numpy (Harris et al. 2020), scipy (Virtanen et al. 2020), astropy (Astropy Collaboration et al. 2013, 2018, 2022), BANZAI (McCully et al. 2018b; McCully et al. 2018a).

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