An ultrahot Neptune in the Neptune desert

2020 • 2020NatAs...4.1148J

Authors • Jenkins, James S. • Díaz, Matías R. • Kurtovic, Nicolás T. • Espinoza, Néstor • Vines, Jose I. • Rojas, Pablo A. Peña • 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 • de Leon, Jerome Pitogo • 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 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 9.0-2.9+2.7?% 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).


IPAC Authors


Jessie Christiansen

Associate Scientist


David Ciardi

Senior Scientist