An ultrahot Neptune in the Neptune desert

Creators: Jenkins, James S.; Díaz, Matías R.; Kurtovic, Nicolás T.; Espinoza, Néstor; Vines, Jose I.; Peña Rojas, Pablo A.; Brahm, Rafael; Torres, Pascal; Cortés-Zuleta, Pía; Soto, Maritza G.; Lopez, Eric D.; King, George W.; Wheatley, Peter J.; Winn, Joshua N.; Ciardi, David R.; Ricker, George; Vanderspek, Roland; Latham, David W.; Seager, Sara; Jenkins, Jon M.; Beichman, Charles A.; Bieryla, Allyson; Burke, Christopher J.; Christiansen, Jessie L.; Henze, Christopher E.; Klaus, Todd C.; McCauliff, Sean; Mori, Mayuko; Narita, Norio; Nishiumi, Taku; Tamura, Motohide; Pitogo de Leon, Jerome; Quinn, Samuel N.; Villaseñor, Jesus Noel; Vezie, Michael; Lissauer, Jack J.; Collins, Karen A.; Collins, Kevin I.; Isopi, Giovanni; Mallia, Franco; Ercolino, Andrea; Petrovich, Cristobal; Jordán, Andrés; Acton, Jack S.; Armstrong, David J.; Bayliss, Daniel; Bouchy, François; Belardi, Claudia; Bryant, Edward M.; Burleigh, Matthew R.; Cabrera, Juan; Casewell, Sarah L.; Chaushev, Alexander; Cooke, Benjamin F.; Eigmüller, Philipp; Erikson, Anders; Foxell, Emma; Gänsicke, Boris T.; Gill, Samuel; Gillen, Edward; Günther, Maximilian N.; Goad, Michael R.; Hooton, Matthew J.; Jackman, James A. G.; Louden, Tom; McCormac, James; Moyano, Maximiliano; Nielsen, Louise D.; Pollacco, Don; Queloz, Didier; Rauer, Heike; Raynard, Liam; Smith, Alexis M. S.; Tilbrook, Rosanna H.; Titz-Weider, Ruth; Turner, Oliver; Udry, Stéphane; Walker, Simon R.; Watson, Christopher A.; West, Richard G.; Palle, Enric; Ziegler, Carl; Law, Nicholas; Mann, Andrew W.

Abstract

About 1 out of 200 Sun-like stars has a planet with an orbital period shorter than one day: an ultrashort-period planet. All of the previously known ultrashort-period planets are either hot Jupiters, with sizes above 10 Earth radii (R⊕), or apparently rocky planets smaller than 2 R⊕. Such lack of planets of intermediate size (the 'hot Neptune desert') has been interpreted as the inability of low-mass planets to retain any hydrogen/helium (H/He) envelope in the face of strong stellar irradiation. Here we report the discovery of an ultrashort-period planet with a radius of 4.6 R⊕ and a mass of 29 M⊕, firmly in the hot Neptune desert. Data from the Transiting Exoplanet Survey Satellite revealed transits of the bright Sun-like star LTT 9779 every 0.79 days. The planet's mean density is similar to that of Neptune, and according to thermal evolution models, it has a H/He-rich envelope constituting 9.0^(+2.7)_(−2.9)% of the total mass. With an equilibrium temperature around 2,000 K, it is unclear how this 'ultrahot Neptune' managed to retain such an envelope. Follow-up observations of the planet's atmosphere to better understand its origin and physical nature will be facilitated by the star's brightness (V_(mag) = 9.8).

Additional Information

© 2020 Nature Publishing Group. Received 09 July 2019; Accepted 01 June 2020; Published 21 September 2020. Funding for the TESS mission is provided by NASA's Science Mission directorate. We acknowledge the use of public TESS alert data from pipelines at the TESS Science Office and at the TESS Science Processing Operations Center. This research has made use of the Exoplanet Follow-up Observation Program website, which is operated by the California Institute of Technology, under contract with the National Aeronautics and Space Administration under the Exoplanet Exploration Program. 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. J.S.J. and N.T. acknowledge support by FONDECYT grants 1161218 and 1201371, and partial support from CONICYT project Basal AFB-170002. M.R.D. is supported by CONICYT-PFCHA/Doctorado Nacional-21140646/Chile and Proyecto Basal AFB-170002. J.I.V. acknowledges support of CONICYT-PFCHA/Doctorado Nacional-21191829. This work was made possible owing to ESO Projects 0102.C-0525 (principal investigator, Díaz) and 0102.C-0451 (principal investigator, Brahm). R.B. acknowledges support from FONDECYT Post-doctoral Fellowship Project 3180246. This work is partly supported by JSPS KAKENHI grant numbers JP18H01265 and JP18H05439, and JST PRESTO grant number JPMJPR1775. The IRSF project is a collaboration between Nagoya University and the South African Astronomical Observatory (SAAO) supported by the Grants-in-Aid for Scientific Research on Priority Areas (A) (numbers 10147207 and 10147214) and Optical and Near-Infrared Astronomy Inter-University Cooperation Program, from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan and the National Research Foundation (NRF) of South Africa. We thank A. Fukui, N. Kusakabe, K. Morihana, T. Nagata, T. Nagayama and the staff of SAAO for their kind support for IRSF SIRIUS observations and analyses. C.P. acknowledges support from the Gruber Foundation Fellowship and Jeffrey L. Bishop Fellowship. This research includes data collected under the NGTS project at the ESO La Silla Paranal Observatory. NGTS is funded by a consortium of institutes consisting of the University of Warwick, the University of Leicester, Queen's University Belfast, the University of Geneva, the Deutsches Zentrum für Luft- und Raumfahrt e.V. (DLR; under the 'Großinvestition GI-NGTS'), the University of Cambridge, together with the UK Science and Technology Facilities Council (STFC; project reference ST/M001962/1 and ST/S002642/1). P.J.W., D.B., B.T.G., S.G., T.L., D.P. and R.G.W. are supported by STFC consolidated grant ST/P000495/1. D.J.A. gratefully acknowledges support from the STFC via an Ernest Rutherford Fellowship (ST/R00384X/1). E.G. gratefully acknowledges support from the David and Claudia Harding Foundation in the form of a Winton Exoplanet Fellowship. M.J.H. acknowledges funding from the Northern Ireland Department for the Economy. M.T. is supported by JSPS KAKENHI (18H05442, 15H02063). A.J., R.B. and P.T. acknowledge support from FONDECYT project 1171208, and by the Ministry for the Economy, Development, and Tourism's Programa Iniciativa Científica Milenio through grant IC 120009, awarded to the Millennium Institute of Astrophysics (MAS). P.E., A.C. and H.R. acknowledge the support of the DFG priority programme SPP 1992 'Exploring the Diversity of Extrasolar Planets' (RA 714/13-1). We acknowledge the effort of A. Tokovinin in helping to perform the observations and reduction of the SOAR data. Data availability: The photometric data that support the findings of this study are publically available from the Mikulski Archive for Space Telescopes (http://archive.stsci.edu/) under the TESS mission link. All radial-velocity data are available from the corresponding author upon reasonable request. Raw and processed spectra can be obtained from the European Southern Observatory's data archive at http://archive.eso.org. Code availability: All codes necessary for the reproduction of this work are publically available through the GitHub repository, as follows: EMPEROR, https://github.com/ReddTea/astroEMPEROR; Juliet, https://github.com/nespinoza/juliet; SPECIES, https://github.com/msotov/SPECIES ; ARIADNE, https://www.github.com/jvines/astroARIADNE. Author Contributions: J.S.J. led the TESS precision radial-velocity follow-up programme, selection of the targets, analysis and project coordination, and wrote the bulk of the paper. M.D., N.T. and R.B. performed the HARPS radial-velocity observations, P.T. observed the star with Coralie and M.D. analysed the activity data from these sources. N.E. performed the global modelling, with P.C.-Z. performing the TTV analysis, and R.B., M.G.S. and A.B. performing the stellar characterization using the spectra and evolutionary models. P.A.P.R. worked on the EMPEROR code and assisted in fitting the HARPS radial velocities. E.D.L. created a structure model for the planet, and in addition to G.W.K. and P.J.W., performed photoevaporation modelling. J.N.W. performed analysis of the system parameters. D.R.C. led the Keck NIRC2 observations and analysis. G.R., R.V., D.W.L., S.S. and J.M.J. have been leading the TESS project, observations, organization of the mission, processing of the data, organization of the working groups, selection of the targets and dissemination of the data products. C.E.H., S.M. and T.K. worked on the SPOC data pipeline. C.J.B. was a member of the TOI discovery team. S.N.Q. contributed to TOI vetting, TFOP organization and TRES spectral analysis. J.L. and C.P. helped with the interpretation of the system formation and evolution. K.A.C. contributed to TOI vetting, TFOP organization, and TFOP SG1 ground-based time-series photometry analysis. G.I., F.M., A.E., K.I.C., M.M., N.N., T.N. and J.P.L. contributed TFOP SG1 observations. J.S.A., D.J.A., D.B., F.B., C.B., E.M.B., M.R.B., J.C., S.L.C., A.C., B.F.C., P.E., A.E., E.F., B.T.G., S.G., E.G., M.N.G., M.R.G., M.J.H., J.A.G.J., T.L., J.M., M.M., L.D.N., D.P., D.Q., H.R., L.R., A.M.S.S., R.H.T., R.T.-W., O.T., S.U., J.I.V., S.R.W., C.A.W., R.G.W., P.J.W. and G.W.K. are part of the NGTS consortium who provided follow-up observations to confirm the planet. E.P. and J.J.L. helped with the interpretation of the result. C.B. performed the observations at SOAR and reduced the data, C.Z. performed the data analysis, and N.L. and A.W.M. assisted in the survey proposal, analysis and telescope time acquisition. All authors contributed to the paper. The authors declare no competing interests.

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An ultrahot Neptune in the Neptune desert

Abstract

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