Artist’s impression of Kepler-78b, an Earth-sized rocky exoplanet discovered by Roberto Sanchis-Ojeda (MIT) using Kepler Space Telescope data, and confirmed by Andrew Howard (UH Institute for Astronomy), et al. Using W. M. Keck Observatory (atop Mauna Kea, HI.) HIRES instrument data and radial velocity method to determine the planet’s mass. Results presented in the Oct. 31, 2013, issue of the journal Nature. Kepler-78b is a member of a new class of “ultrashort period” of planets that orbit their star in less than 12 hours. It is the first of these planets to have both size and mass measured. With a radius about 1.2 x Earth and a mass about 1.7 x Earth, Kepler-78b has a density that is the same as Earth’s, suggesting that it also made primarily of rock and iron. It orbits its star every 8.5 hrs. Its star is slightly smaller and less massive than the sun and is located about 400 light-years from Earth in the constellation Cygnus.