Exploring exoplanet populations with NASA's Kepler Mission

Abstract

The Kepler Mission is exploring the diversity of planets and planetary systems. Its legacy will be a catalog of discoveries sufficient for computing planet occurrence rates as a function of size, orbital period, star type, and insolation flux. The mission has made significant progress toward achieving that goal. Over 3,500 transiting exoplanets have been identified from the analysis of the first 3 y of data, 100 planets of which are in the habitable zone. The catalog has a high reliability rate (85-90% averaged over the period/radius plane), which is improving as follow-up observations continue. Dynamical (e.g., velocimetry and transit timing) and statistical methods have confirmed and characterized hundreds of planets over a large range of sizes and compositions for both single- and multiple-star systems. Population studies suggest that planets abound in our galaxy and that small planets are particularly frequent. Here, I report on the progress Kepler has made measuring the prevalence of exoplanets orbiting within one astronomical unit of their host stars in support of the National Aeronautics and Space Administration's long-term goal of finding habitable environments beyond the solar system.

Keywords: planet detection; transit photometry.

Fig. 1.

Non-Kepler exoplanet discoveries (Left) are plotted as mass versus orbital period, colored according to the detection technique. A simplified mass–radius relation is used to transform planetary mass to radius (Right), and the >3,500 Kepler discoveries (yellow) are added for comparison. Eighty-six percent of the non-Kepler discoveries are larger than Neptune, whereas the inverse is true of the Kepler discoveries: 85% are smaller than Neptune.

Fig. 2.

Stellar effective temperature versus insolation (stellar flux at the semimajor axis) for Kepler exoplanets larger than 2 R_⊕ (plusses) and smaller than 2 R_⊕ (circles). Symbols are colored blue if they lie within the HZ and are sized relative to the Earth (represented by a superimposed image) if they represent a planet smaller than 2 R_⊕. The confirmed HZ exoplanets (Kepler-22b, Kepler-62 e and f, Kepler-61b, and Kepler-186f) are displayed as the artist’s conceptions.

Fig. 3.

The radius distribution (Left) and period distribution (Right) of planet occurrence rates expressed as the average number of planets per star. The distributions have been marginalized over periods between 0.68 and 50 d (radius distribution) and radii between 0.5 and 22.6 R_⊕ (period distribution). H12 refers to ref. , F13 refers to ref. , and D13 refers to ref. . The reported one-sigma uncertainties are shown.