Friday, July 29, 2016

The Tightly-Spaced Planets of Kepler-80

Kepler has discovered many planetary systems consisting of multiple small planets with orbital periods less than ~50 days. These compact planetary systems are known as Systems with Tightly-spaced Inner Planets (STIPs). Kepler-80 (KOI-500) is one such STIP. It consists of 5 transiting planets identified as planets "f", "d", "e", "b", and "c"; and their orbital periods are 1.0, 3.1, 4.6, 7.1, and 9.5 days, respectively. Additionally, the 5 planets have ~1.21, ~1.53, ~1.60, ~2.67, and ~2.74 times the radius of Earth, respectively.

Measurements of the transit times and transit timing variation (TTV) analysis indicate that the outer four planets ("d", "e", "b", and "c") have ~6.75, ~4.13, ~6.93, and ~6.74 times the mass of Earth, respectively. The similar masses but different radii is consistent with planets "d" and "e" having Earth-like compositions, and planets "b" and "c" with Earth-like cores surrounded by ~2 percent (by mass) hydrogen-helium envelopes. The orbits of the four outer planets are also in a rare dynamical configuration. The host star of this planetary system is a K5 main sequence star located ~1200 light years away. It has 0.678 times the radius, 0.730 times the mass and 0.170 times the luminosity of the Sun, and its effective temperature is 4540 K.

MacDonald et al. (2016), "A Dynamical Analysis of the Kepler-80 System of Five Transiting Planets”, arXiv:1607.07540 [astro-ph.EP]