  We report the discovery of a transiting planet orbiting the star TYC
6446-326-1. The star, WASP-22, is a moderately bright (V=12.0) solar-type star
(Teff = 6000 +/- 100 K, [Fe/H] = -0.05 +/- 0.08). The lightcurve of the star
obtained with the WASP-South instrument shows periodic transit-like features
with a depth of about 1 and a duration of 0.14 days. The presence of a
transit-like feature in the lightcurve is confirmed using z-band photometry
obtained with Faulkes Telescope South. High resolution spectroscopy obtained
with the CORALIE and HARPS spectrographs confirm the presence of a planetary
mass companion with an orbital period of 3.533 days in a near-circular orbit.
From a combined analysis of the spectroscopic and photometric data assuming
that the star is a typical main-sequence star we estimate that the planet has a
mass M_p = 0.56 +/- 0.02 M_Jup and a radius R_p = 1.12 +/- 0.04 R_Jup. In
addition, there is a linear trend of 40 m/s/yr in the radial velocities
measured over 16 months, from which we infer the presence of a third body with
a long period orbit in this system. The companion may be a low mass M-dwarf, a
white dwarf or a second planet.
