Program: GN-2021B-Q-232

Among the cornucopia of exoplanet varieties discovered in the past decade, the ultra-hot Jupiters (UHJs) stand out for their extreme properties. UHJs have equilibrium dayside temperatures of > 2200 K and day-to-night side temperature gradients of ~1000 K. Such high temperatures mean that the molecules on the stellar-facing hemisphere are mostly dissociated, making the spectral properties of UHJs more akin to low-mass stars than cooler Jupiter-mass planets. UHJs have also emerged as rich targets for transmission spectroscopy due to their extended atmospheres and the variety of observable atomic metal transitions. Despite their popularity as transmission spectroscopy targets, few studies have been able to derive useful empirical information about the velocity dynamics in these extreme atmospheres. We propose to observe a transit of the UHJ HAT-P-70 b in order to produce the first transmission spectrum for this planet and measure thee velocity flows in its extended atmosphere. HAT-P-70 b is highly inflated, with a radius of ~1.9 Jupiter radii and a dayside temperature of ~2500 K. Based on our past work quantifying the velocity flows in UHJ atmospheres, we expect to detect rotational velocities in excess of the planet's tidally-locked value. Constraints on HAT-P-70 b's velocity dynamics will provide another crucial data point for understanding the physics of UHJ atmospheres.