The paper reports the discovery of an extrasolar planet, XO-2b, transiting a bright, early K dwarf star, XO-2. The planet has a radius of 0.98 Jupiter radii and a mass of 0.57 Jupiter masses, with an orbital period of 2.615857 ± 0.000005 days. XO-2 is characterized by high metallicity ([Fe/H] = 0.45 ± 0.02), high proper motion ($\mu_{tot} = 157$ mas yr$^{-1}$), and a common proper motion stellar companion with a separation of 31". The two stars are nearly identical in spectral type and apparent magnitude. The high metallicity of XO-2 suggests that it has a mass and radius close to the solar values, $M_* = 0.98 \pm 0.02$ M$_\odot$ and $R_* = 0.97 \pm 0.02$ R$_\odot$. The high proper motion of XO-2 is attributed to an eccentric orbit confined to the Galactic disk. The phase space position of XO-2 suggests it originated in the metal-rich inner Thin Disk and was subsequently scattered into the solar neighborhood. The paper describes an efficient Markov Chain Monte Carlo algorithm for calculating the Bayesian posterior probability of the system parameters from transit light curve data. The analysis confirms the planetary mass of XO-2b and refine the ephemeris, while ruling out the possibility of a background line-of-sight binary. The high space velocity of XO-2 suggests it belongs to the Thick Disk, but its orbit is well confined to the Galactic plane. The findings support the idea that metal-enhanced dynamical streams should be overabundant in detectable extrasolar planets.The paper reports the discovery of an extrasolar planet, XO-2b, transiting a bright, early K dwarf star, XO-2. The planet has a radius of 0.98 Jupiter radii and a mass of 0.57 Jupiter masses, with an orbital period of 2.615857 ± 0.000005 days. XO-2 is characterized by high metallicity ([Fe/H] = 0.45 ± 0.02), high proper motion ($\mu_{tot} = 157$ mas yr$^{-1}$), and a common proper motion stellar companion with a separation of 31". The two stars are nearly identical in spectral type and apparent magnitude. The high metallicity of XO-2 suggests that it has a mass and radius close to the solar values, $M_* = 0.98 \pm 0.02$ M$_\odot$ and $R_* = 0.97 \pm 0.02$ R$_\odot$. The high proper motion of XO-2 is attributed to an eccentric orbit confined to the Galactic disk. The phase space position of XO-2 suggests it originated in the metal-rich inner Thin Disk and was subsequently scattered into the solar neighborhood. The paper describes an efficient Markov Chain Monte Carlo algorithm for calculating the Bayesian posterior probability of the system parameters from transit light curve data. The analysis confirms the planetary mass of XO-2b and refine the ephemeris, while ruling out the possibility of a background line-of-sight binary. The high space velocity of XO-2 suggests it belongs to the Thick Disk, but its orbit is well confined to the Galactic plane. The findings support the idea that metal-enhanced dynamical streams should be overabundant in detectable extrasolar planets.