Detection of a transit of the super-Earth 55 Cancri e with warm Spitzer

We report on the detection of a transit of the super-Earth 55 Cnc e with warm Spitzer in IRAC's 4.5 mu m band. Our MCMC analysis includes an extensive modeling of the systematic effects affecting warm Spitzer photometry, and yields a transit depth of 410 +/- 63 ppm, which translates to a planetary radius of 2.08(-0.17)(+0.16) R-circle plus as measured in IRAC 4.5 mu m channel. A planetary mass of 7.81(-0.53)(+0.58) M-circle plus is derived from an extensive set of radial-velocity data, yielding a mean planetary density of 4.78(-1.20)(+1.31) g cm(-3). Thanks to the brightness of its host star (V = 6, K = 4), 55 Cnc e is a unique target for the thorough characterization of a super-Earth orbiting around a solar-type star.