Contributed Talk - Splinter Exoplanets

Wednesday, 20 September 2017, 15:20   (HS1)

An Earth-sized planet transiting an M-dwarf in a 4.3-hour orbit

A. M. S. Smith1, J. Cabrera1, Sz. Csizmadia1, F. Dai2, D. Gandolfi3, T. Hirano4, J. N. Winn5, S. Albrecht6, R. Alonso7,8, G. Antoniciello3, O. Barrag\'an3, H. Deeg7,8, Ph. Eigmüller1, M. Endl9, A. Erikson1, M. Fridlund10,11,7, A. Fukui12, S. Grziwa13, E. W. Guenther14, A. P. Hatzes14, D. Hidalgo7,8, A. W. Howard15, H. Isaacson16, J. Korth13, M. Kuzuhara17,18, J. Livingston19, N. Narita19,17,18, D. Nespral 7,8, G. Nowak7,8, E. Palle7,8, M. Pätzold13, C.M. Persson11, E. Petigura20, J. Prieto-Arranz7,8, H. Rauer1,21, I. Ribas22, and V. Van~Eylen10
1Institute of Planetary Research, DLR, Berlin; 2MIT, USA; 3Universitá di Torino, Italy; 4Tokyo Institute of Technology, Japan; 5Princeton University, USA; 6Aarhus University, Denmark; 7IAC, Tenerife, Spain; 8Universidad de La Laguna, Spain; 9University of Texas at Austin, USA; 10Leiden University, The Netherlands; 11Chalmers University of Technology, Onsala, Sweden; 12National Astronomical Observatory of Japan, Okayama; 13Universität zu Köln; 14Thüringer Landessternwarte Tautenburg; 15Astronomy, Caltech, USA; 16UC Berkeley, USA; 17Astrobiology Center, Mitaka, Japan; 18National Astronomical Observatory of Japan, Mitaka; 19University of Tokyo, Japan; 20Geological and Planetary Sciences, Caltech, USA; 21TU Berlin; 22Institut de Ci\`encies de l'Espai, Bellaterra, Spain

We report the discovery from K2 of a transiting terrestrial planet in an ultra-short-period orbit around an M3-dwarf. The planet completes each orbit in just 4.3~hours, the second-shortest orbital period of any known planet, only 4~minutes longer than that of KOI~1843.03, which also orbits an M-dwarf. Using a combination of imaging, RV measurements, and light curve modelling, we show that no plausible eclipsing binary scenario can explain the K2 light curve, and thus confirm the planetary nature of the system. The short-period orbit of the planet, whose radius we determine to be 0.89 \pm 0.09~\mathrmR_\rm \oplus, allows us to place constraints on its composition - we find it must be composed of at least 45 % iron. We also discuss the possible implications of the surprising fact that the two shortest-period planets known both orbit M-dwarfs.