  We present the discovery of KELT-22Ab, a hot Jupiter from the KELT-South
survey. KELT-22Ab transits the moderately bright ($V\sim 11.1$) Sun-like G2V
star TYC 7518-468-1. The planet has an orbital period of $P = 1.3866529 \pm
0.0000027 $ days, a radius of $R_{P} = 1.285_{-0.071}^{+0.12}~R_{J}$, and a
relatively large mass of $M_{P} = 3.47_{-0.14}^{+0.15}~ M_{J}$. The star has
$R_{\star} = 1.099_{-0.046}^{+0.079}~ R_{\odot}$, $M_{\star} =
1.092_{-0.041}^{+0.045}~ M_{\odot}$, ${T_{\rm eff}\,} = 5767_{-49}^{+50}~$ K,
${\log{g_\star}} = 4.393_{-0.060}^{+0.039}~$ (cgs), and [m/H] =
$+0.259_{-0.083}^{+0.085}~$, and thus, other than its slightly super-solar
metallicity, appears to be a near solar twin. Surprisingly, KELT-22A exhibits
kinematics and a Galactic orbit that are somewhat atypical for thin disk stars.
Nevertheless, the star is rotating quite rapidly for its estimated age, shows
evidence of chromospheric activity, and is somewhat metal rich. Imaging reveals
a slightly fainter companion to KELT-22A that is likely bound, with a projected
separation of 6\arcsec ($\sim$1400 AU). In addition to the orbital motion
caused by the transiting planet, we detect a possible linear trend in the
radial velocity of KELT-22A suggesting the presence of another relatively
nearby body that is perhaps non-stellar. KELT-22Ab is highly irradiated (as a
consequence of the small semi-major axis of $a/R_{\star} = 4.97$), and is
mildly inflated. At such small separations, tidal forces become significant.
The configuration of this system is optimal for measuring the rate of tidal
dissipation within the host star. Our models predict that, due to tidal forces,
the semi-major axis of KELT-22Ab is decreasing rapidly, and is thus predicted
to spiral into the star within the next Gyr.
