An Ultra-Hot Neptune in the Neptune desert
Creators: name: Jenkins, James S.
name: Díaz, Matías R.
name: Kurtovic, Nicolás T.
name: Espinoza, Néstor
name: Vines, Jose I.
name: Rojas, Pablo A. Peña
name: Brahm, Rafael
name: Torres, Pascal
name: Cortés-Zuleta, Pía
name: Soto, Maritza G.
name: Lopez, Eric D.
name: King, George W.
name: Wheatley, Peter J.
name: Winn, Joshua N.
name: Ciardi, David R.
name: Ricker, George
name: Vanderspek, Roland
name: Latham, David W.
name: Seager, Sara
name: Jenkins, Jon M.
name: Beichman, Charles A.
name: Bieryla, Allyson
name: Burke, Christopher J.
name: Christiansen, Jessie L.
name: Henze, Christopher E.
name: Klaus, Todd C.
name: McCauliff, Sean
name: Mori, Mayuko
name: Narita, Norio
name: Nishiumi, Taku
name: Tamura, Motohide
name: de Leon, Jerome Pitogo
name: Quinn, Samuel N.
name: Villaseñor, Jesus Noel
name: Vezie, Michael
name: Lissauer, Jack J.
name: Collins, Karen A.
name: Collins, Kevin I.
name: Isopi, Giovanni
name: Mallia, Franco
name: Ercolino, Andrea
name: Petrovich, Cristobal
name: Jordán, Andrés
name: Acton, Jack S.
name: Armstrong, David J.
name: Bayliss, Daniel
name: Bouchy, François
name: Belardi, Claudia
name: Bryant, Edward M.
name: Burleigh, Matthew R.
name: Cabrera, Juan
name: Casewell, Sarah L.
name: Chaushev, Alexander
name: Cooke, Benjamin F.
name: Eigmüller, Philipp
name: Erikson, Anders
name: Foxell, Emma
name: Gänsicke, Boris T.
name: Gill, Samuel
name: Gillen, Edward
name: Günther, Maximilian N.
name: Goad, Michael R.
name: Hooton, Matthew J.
name: Jackman, James A. G.
name: Louden, Tom
name: McCormac, James
name: Moyano, Maximiliano
name: Nielsen, Louise D.
name: Pollacco, Don
name: Queloz, Didier
name: Rauer, Heike
name: Raynard, Liam
name: Smith, Alexis M. S.
name: Tilbrook, Rosanna H.
name: Titz-Weider, Ruth
name: Turner, Oliver
name: Udry, Stéphane
name: Walker, Simon. R.
name: Watson, Christopher A.
name: West, Richard G.
name: Palle, Enric
name: Ziegler, Carl
name: Law, Nicholas
name: Mann, Andrew W.
Publisher: name: arXiv
Year: 2020
Subjects: subject: Earth and Planetary Astrophysics (astro-ph.EP)
subject: Solar and Stellar Astrophysics (astro-ph.SR)
subject: FOS: Physical sciences
subject: FOS: Physical sciences

description: About one out of 200 Sun-like stars has a planet with an orbital period shorter than one day: an ultra-short-period planet (Sanchis-ojeda et al. 2014; Winn et al. 2018). All of the previously known ultra-short-period planets are either hot Jupiters, with sizes above 10 Earth radii (Re), or apparently rocky planets smaller than 2 Re. 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 ultra-short-period planet with a radius of 4.6 Re and a mass of 29 Me, firmly in the hot Neptune desert. Data from the Transiting Exoplanet Survey Satellite (Ricker et al. 2015) revealed transits of the bright Sun-like star \starname\, 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 2000 K, it is unclear how this "ultra-hot 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 (Vmag=9.8).
description: 26 pages, 10 figures, 3 tables. Published in Nature Astronomy (21/09/2020)