Kepler Planet-Detection Mission: Introduction and First Results

TLDR

The habitable zone is the region where planetary temperatures are suitable for water to exist on a planet's surface. The Kepler mission was designed to determine the frequency of Earth‑sized planets in and near the habitable zone of Sun‑like stars. During the first six weeks of observations, Kepler monitored 156,000 stars and discovered five new exoplanets with sizes between 0.37 and 1.6 Jupiter radii and orbital periods from 3.2 to 4.9 days. Kepler discovered five short‑period exoplanets, including Neptune‑sized Kepler‑4b with a density similar to Neptune despite extreme irradiation, the low‑density Kepler‑7b (~0.17 g cm⁻³), and Kepler‑5b, ‑6b, and ‑8b, all confirming planets with densities below gas‑giant predictions.

Abstract

The Kepler mission was designed to determine the frequency of Earth-sized planets in and near the habitable zone of Sun-like stars. The habitable zone is the region where planetary temperatures are suitable for water to exist on a planet's surface. During the first 6 weeks of observations, Kepler monitored 156,000 stars, and five new exoplanets with sizes between 0.37 and 1.6 Jupiter radii and orbital periods from 3.2 to 4.9 days were discovered. The density of the Neptune-sized Kepler-4b is similar to that of Neptune and GJ 436b, even though the irradiation level is 800,000 times higher. Kepler-7b is one of the lowest-density planets (approximately 0.17 gram per cubic centimeter) yet detected. Kepler-5b, -6b, and -8b confirm the existence of planets with densities lower than those predicted for gas giant planets.