NGTS-4b: A sub-Neptune transiting in the desert
Jackman, James A. G.; Wheatley, Peter J.; Bayliss, Daniel; Moyano, Maximiliano; Günther, Maximilian N.; Cabrera, Juan; Csizmadia, Szilard; Eigmüller, Philipp; Erikson, Anders; Rauer, Heike; Casewell, Sarah L.; Goad, Michael R.; Armstrong, David J.; Burleigh, Matthew R.; Gillen, Edward; Jenkins, James S.; McCormac, James; Udry, Stéphane; West, Richard G.; Gillon, Michaël; Delrez, Laetitia; Ducrot, Elsa; Smith, Alexis M. S.; Gänsicke, Boris T.; Jehin, Emmanuël; Queloz, Didier; Watson, Christopher A.; Chazelas, Bruno; Lambert, Gregory; Bouchy, François; Chaushev, Alexander; Chote, Paul; Foxell, Emma; Hodgkin, Simon T.; Louden, Tom; Nielsen, Louise D.; Raynard, Liam; Soto, Maritza; Pollacco, Don; Briegal, Joshua T.; Turner, Oliver; Burdanov, Artem; Murray, Catriona; Almleaky, Yaseen; Cooke, Benjamin F.; Sohy, Sandrine; Thompson, Samantha J.; Belardi, Claudia; Walker, Simon R.; King, George; Longstaff, Emma S.
United Kingdom, Chile, Switzerland, Germany, Saudi Arabia, Belgium
Abstract
We report the discovery of NGTS-4b, a sub-Neptune-sized planet transiting a 13th magnitude K-dwarf in a 1.34 d orbit. NGTS-4b has a mass M = 20.6 ± 3.0 M⊕ and radius R = 3.18 ± 0.26 R⊕, which places it well within the so-called `Neptunian Desert'. The mean density of the planet (3.45 ± 0.95 g cm-3) is consistent with a composition of 100 per cent 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 per cent, 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.