About 1 out of 200 Sun-like stars has a planet with an orbital period shorter than one day: an ultrashort-period planet(1,2). All of the previously known ultrashort-period planets are either hot Jupiters, with sizes above 10 Earth radii (R-circle plus), or apparently rocky planets smaller than 2 R-circle plus. 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-circle plus and a mass of 29 M-circle plus, firmly in the hot Neptune desert. Data from the Transiting Exoplanet Survey Satellite(3) 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 (V-mag = 9.8).
es_ES
Patrocinador
dc.description.sponsorship
NASA's Science Mission directorate
NASA High-End Computing (HEC) Program through the NASA Advanced Supercomputing (NAS) Division at Ames Research Center
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)
CONICYT FONDECYT
1171208
1161218
1201371
3180246
CONICYT project Basal
AFB-170002
CONICYT-PFCHA/Doctorado Nacional/Chile
21140646
Comisión Nacional de Investigación Científica y Tecnológica (CONICYT)
CONICYT PIA/BASAL
AFB-170002
CONICYT-PFCHA/Doctorado Nacional
21191829
ESO Projects
0102.C-0525
0102.C-0451
Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT)
Japan Society for the Promotion of Science
Grants-in-Aid for Scientific Research (KAKENHI)
JP18H01265
JP18H05439
18H05442
15H02063
Japan Science & Technology Agency (JST)
JPMJPR1775
Optical and Near-Infrared Astronomy Inter-University Cooperation Program
Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT)
National Research Foundation - South Africa
Gruber Foundation Fellowship
Jeffrey L. Bishop Fellowship
University of Warwick
University of Leicester
Queen's University Belfast
University of Geneva
Deutsches Zentrum fur Luft-und Raumfahrt e.V. (DLR; under the 'Grossinvestition GI-NGTS')
University of Cambridge
Science & Technology Facilities Council (STFC)
ST/M001962/1
ST/S002642/1
Science & Technology Facilities Council (STFC)
ST/P000495/1
STFC via an Ernest Rutherford Fellowship
ST/R00384X/1
David and Claudia Harding Foundation in the form of a Winton Exoplanet Fellowship
Northern Ireland Department for the Economy
Ministry for the Economy, Development, and Tourism's Programa Iniciativa Cientifica Milenio
IC 120009
German Research Foundation (DFG)
SPP 1992
RA 714/13-1
10147207
10147214
Ministry of Education, Culture, Sports, Science and Technology, Japan (MEXT)
Japan Society for the Promotion of Science
Grants-in-Aid for Scientific Research (KAKENHI)
10147214