KEPLER-93b: A TERRESTRIAL WORLD MEASURED TO WITHIN 120 km, AND A TEST CASE FOR A NEW SPITZER OBSERVING MODE

We present the characterization of the Kepler-93 exoplanetary system, based on three years of photometry gathered by the Kepler spacecraft. We conduct an asteroseismic analysis of the Kepler photometry and conclude that the star has an average density of 1.652 + or - 0.006 g cm super(-3). Its mass of 0.911 + or - 0.033 M sub([middot in circle]) renders it one of the lowest-mass subjects of asteroseismic study. We observed seven transits of Kepler-93b with Spitzer, three of which we conducted in a new observing mode. The pointing strategy we employed to gather this subset of observations halved our uncertainty on the transit radius ratio R sub(P)/R sub(*). We find, after folding together the stellar radius measurement of 0.919 + or - 0.011 R sub([middot in circle]) with the transit depth, a best-fit value for the planetary radius of 1.481 + or - 0.019 M sub([oplus]). After applying a prior on the plausible maximum densities of similarly sized worlds between 1 and 1.5 R sub([oplus]), we find that Kepler-93b possesses an average density within this group.