We report the discovery of NGTS-4b, a sub-Neptune-sized planet transiting a 13th magnitude K-dwarf in a 1.34d orbit. NGTS-4b has a mass M=20.6±3.0M_E and radius R=3.18±0.26R_E, which places it well within the so-called "Neptunian Desert". The mean density of the planet (3.45±0.95g/cm^3) is consistent with a composition of 100% H2O or a rocky core with a volatile envelope. NGTS-4b is likely to suffer significant mass loss due to relatively strong EUV/X-ray irradiation. Its survival in the Neptunian desert may be due to an unusually high core mass, or it may have avoided the most intense X-ray irradiation by migrating after the initial activity of its host star had subsided. With a transit depth of 0.13±0.02%, NGTS-4b represents the shallowest transiting system ever discovered from the ground, and is the smallest planet discovered in a wide-field ground-based photometric survey.
@article{arxiv.1809.00678,
title = {NGTS-4b: A sub-Neptune Transiting in the Desert},
author = {Richard G. West and Edward Gillen and Daniel Bayliss and Matthew R. Burleigh and Laetitia Delrez and Maximilian N. Günther and Simon T. Hodgkin and James A. G. Jackman and James S. Jenkins and George King and James McCormac and Louise D. Nielsen and Liam Raynard and Alexis M. S. Smith and Maritza Soto and Oliver Turner and Peter J. Wheatley and Yaseen Almleaky and David J. Armstrong and Claudia Belardi and François Bouchy and Joshua T. Briegal and Artem Burdanov and Juan Cabrera and Sarah L. Casewel and Alexander Chaushev and Bruno Chazelas and Paul Chote and Benjamin F. Cooke and Szilard Csizmadia and Elsa Ducrot and Philipp Eigmüller and Anders Erikson and Emma Foxell and Boris T. Gänsicke and Michaël Gillon and Michael R. Goad and Emmanuël Jehin and Gregory Lambert and Emma S. Longstaff and Tom Louden and Maximiliano Moyano and Catriona Murray and Don Pollacco and Didier Queloz and Heike Rauer and Sandrine Sohy and Samantha J. Thompson and Stéphane Udry and Simon. R. Walker and Christopher A. Watson},
journal= {arXiv preprint arXiv:1809.00678},
year = {2019}
}