posted on 2021-02-25, 09:24authored byJames S Jenkins, Matias R Diaz, Nicolas T Kurtovic, Nestor Espinoza, Jose I Vines, Pablo A Pena Rojas, Rafael Brahm, Pascal Torres, Pia Cortes-Zuleta, Maritza G Soto, Eric D Lopez, George W King, Peter J Wheatley, Joshua N Winn, David R Ciardi, George Ricker, Roland Vanderspek, David W Latham, Sara Seager, Jon M Jenkins, Charles A Beichman, Allyson Bieryla, Christopher J Burke, Jessie L Christiansen, Christopher E Henze, Todd C Klaus, Sean McCauliff, Mayuko Mori, Norio Narita, Taku Nishiumi, Motohide Tamura, Jerome Pitogo de Leon, Samuel N Quinn, Jesus Noel Villasenor, Michael Vezie, Jack J Lissauer, Karen A Collins, Kevin I Collins, Giovanni Isopi, Franco Mallia, Andrea Ercolino, Cristobal Petrovich, Andres Jordan, Jack S Acton, David J Armstrong, Daniel Bayliss, Francois Bouchy, Claudia Belardi, Edward M Bryant, Matthew R Burleigh, Juan Cabrera, Sarah L Casewell, Alexander Chaushev, Benjamin F Cooke, Philipp Eigmueller, Anders Erikson, Emma Foxell, Boris T Gansicke, Samuel Gill, Edward Gillen, Maximilian N Guenther, Michael R Goad, Matthew J Hooton, James AG Jackman, Tom Louden, James McCormac, Maximiliano Moyano, Louise D Nielsen, Don Pollacco, Didier Queloz, Heike Rauer, Liam Raynard, Alexis MS Smith, Rosanna H Tilbrook, Ruth Titz-Weider, Oliver Turner, Stephane Udry, Simon R Walker, Christopher A Watson, Richard G West, Enric Palle, Carl Ziegler, Nicholas Law, Andrew W Mann
About 1 out of 200 Sun-like stars has a planet with an orbital period shorter than one day: an ultrashort-period planet1,2. 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 Satellite3 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 (Vmag = 9.8).
Correction to: Nature Astronomy https://doi.org/10.1038/s41550-020-1142-z, published online 21 September 2020.
In the version of this Letter originally published, the present address of Rafael Brahm, ‘Facultad de Ingeniería y Ciencias, Universidad Adolfo Ibáñez, Peñalolén, Chile’, was not listed. This has now been corrected.