A Super-Earth Transiting a Naked-Eye Star
(14 votes over all institutions)
We have detected transits of the innermost planet “e” orbiting 55 Cnc (V=6.0), based on two weeks of precise photometric monitoring with the MOST space telescope. The transits of 55 Cnc e occur with the period (0.74 d) and phase that had been predicted by Dawson & Fabrycky, and with the expected duration and depth for the crossing of a Sun-like star by a hot super-Earth. Assuming the star’s mass and radius to be 0.96 +/- 0.10 Msun and 1.10 +/- 0.10 Rsun, the planet’s mass, radius, and mean density are 8.57 +/- 0.64 Me, 1.63 +/- 0.16 Re, and 10.9 +/- 3.1 g/cm^3. The high density suggests the planet has a rock-iron composition as opposed to hydrogen, water, or other light elements. This makes 55 Cnc e similar to the other transiting super-Earths in tight orbits around G stars (Kepler-10b and Corot-7b), and unlike the lower-density super-Earths that are less strongly irradiated (GJ 1214b and Kepler-11d,e,f). The host star of 55 Cnc e is far brighter than that of any other known transiting planet, which will facilitate further investigations.
