An Eccentric Massive Jupiter Orbiting a Sub-Giant on a 9.5 Day Period Discovered in the Transiting Exoplanet Survey Satellite Full Frame Images

We report the discovery of TOI-172 b from the Transiting Exoplanet Survey Satellite (TESS) mission, a massive hot Jupiter transiting a slightly evolved G-star with a 9.48-day orbital period. This is the first planet to be confirmed from analysis of only the TESS full frame images, because the host star was not chosen as a two minute cadence target. From a global analysis of the TESS photometry and follow-up observations carried out by the TESS Follow-up Observing Program Working Group, TOI-172 (TIC 29857954) is a slightly evolved star with an effective temperature of $T_{\mathrm{e}\mathrm{f}\mathrm{f}}$ =$5645\pm 50$ K, a mass of $M_{\star }$ = $1.128_{-0.061}^{+0.065}$ $M_{\odot }$, radius of $R_{\star }$ = $1.777_{-0.044}^{+0.047}$ $R_{\odot }$, a surface gravity of $\log$ $g_{\star }$ = $3.993_{-0.028}^{+0.027}$, and an age of $7.4_{-1.5}^{+1.6}$ Gyr. Its planetary companion (TOI-172 b) has a radius of $R_{\mathrm{P}}$ = $0.965_{-0.029}^{+0.032}$ $R_{\mathrm{J}}$, a mass of $M_{\mathrm{P}}$ = $5.42_{-0.20}^{+0.22}$ $M_{\mathrm{J}}$, and is on an eccentric orbit ($e = 0.3806^{+0.0093}_{-0.0090}$). TOI-172 b is one of the few known massive giant planets on a highly eccentric short-period orbit. Future study of the atmosphere of this planet and its system architecture offer opportunities to understand the formation and evolution of similar systems.