Douglas Caldwell


Douglas Caldwell, NASA-SETI

The Kepler Mission: Searching for Planets using 17th Century Physics (with a few modern twists)

The discovery of the first exoplanets in the 1990's confirmed that giant planets were common in the Galaxy but left open the question of the prevalence of terrestrial planets. NASA's Kepler Mission was launched in March 2009 to determine the frequency of Earth-size planets orbiting within the habitable zone of their parent stars. Kepler monitors more than 100,000 stars nearly continuously, searching for the small drop in brightness as the planet passes in front of, i.e., transits, its host star. Using essentially the same methods described by Johannes Kepler and put into practice during the 17th and 18th century transits of Venus, we determine the planet's size, orbital period, and orbital semi-major axis.  Using simple energy balance arguments developed in the 19th century, we estimate the equilibrium temperature of the discovered planets. In special cases, we can use 20th century relativity to directly determine the mass of planets from the transit light curve alone. To date, Kepler has discovered more than 1,200 planet candidates; somewhat surprisingly, more than 400 of them are in multiple planet systems. As Kepler's observations continue, we will be able to answer the question of whether Earth-size planets are common, or whether we really do live in a geocentric universe.