Kipping, D. M.2; Torres, G.2; Buchhave, L. A.8; Kenyon, S. J.2; Henze, C.9; Isaacson, H.5; Kolbl, R.5; Marcy, G. W.5; Bryson, S. T.9; Stassun, K.10; Bastien, F.7
1 Astrophysics and Planetary Science, The Niels Bohr Institute, Faculty of Science, Københavns Universitet2 Harvard-Smithsonian Center for Astrophysics3 Natural History Museum of Denmark, Natural History Museum of Denmark, Faculty of Science, Københavns Universitet4 NASA Ames Research Center5 University of California, Berkeley6 Vanderbilt University7 Fisk University, Nashville8 Natural History Museum of Denmark, Natural History Museum of Denmark, Faculty of Science, Københavns Universitet9 NASA Ames Research Center10 Vanderbilt University
In most theories of planet formation, the snow-line represents a boundary between the emergence of the interior rocky planets and the exterior ice giants. The wide separation of the snow-line makes the discovery of transiting worlds challenging, yet transits would allow for detailed subsequent characterization. We present the discovery of Kepler-421b, a Uranus-sized exoplanet transiting a G9/K0 dwarf once every 704.2 days in a near-circular orbit. Using public Kepler photometry, we demonstrate that the two observed transits can be uniquely attributed to the 704.2 day period. Detailed light curve analysis with BLENDER validates the planetary nature of Kepler-421b to >4σ confidence. Kepler-421b receives the same insolation as a body at ~2 AU in the solar system, as well as a Uranian albedo, which would have an effective temperature of ~180 K. Using a time-dependent model for the protoplanetary disk, we estimate that Kepler-421b's present semi-major axis was beyond the snow-line after ~3 Myr, indicating that Kepler-421b may have formed at its observed location.