  We report on the discovery of WASP-12b, a new transiting extrasolar planet
with $R_{\rm pl}=1.79 \pm 0.09 R_J$ and $M_{\rm pl}=1.41 \pm 0.1 M_J$. The
planet and host star properties were derived from a Monte Carlo Markov Chain
analysis of the transit photometry and radial velocity data. Furthermore, by
comparing the stellar spectrum with theoretical spectra and stellar evolution
models, we determined that the host star is a super-solar metallicity
([M/H]$=0.3^{+0.05}_{-0.15}$), late-F (T$_{\rm eff}=6300^{+200}_{-100}$ K) star
which is evolving off the zero age main sequence. The planet has an equilibrium
temperature of T$_{\rm eq}$=2516 K caused by its very short period orbit
($P=1.09$ days) around the hot, 12th magnitude host star. WASP-12b has the
largest radius of any transiting planet yet detected. It is also the most
heavily irradiated and the shortest period planet in the literature.
