The HD 60779 Planetary System: A Transiting Sub-Neptune on a 30 Day Orbit and a More Massive Outer World

We present the discovery of the planetary system orbiting the bright (V = 7.2), nearby (35 pc), Sun-like (M⋆ = 1.050 ± 0.044 M⊙, R⋆ = 1.129 ± 0.013 R⊙) star, HD 60779. We report two Transiting Exoplanet Survey Satellite transits and a subsequent Characterising Exoplanet Satellite transit of HD 60779 b, a sub-Neptune ( (Formula presented) 3.246−0.097+0.100R⊕ ) planet on a (Formula presented) 29.986175−0.000033+0.000030day orbit. Additionally, 313 High Accuracy Radial velocity Planet Searcher for the Northern hemisphere radial velocity (RV) measurements reveal the mass of planet b ( (Formula presented) 14.19−0.96+0.97M⊕ ) and the presence of an outer planet, HD 60779 c (Porb = 104.79 ± 0.23 days, (Formula presented) Mpsini=28.3±1.5M⊕ ). Both of these planets’ orbits are consistent with being circular, suggesting that they have a dynamically quiet history. The data are not sufficient to determine whether planet c transits. HD 60779’s uniquely high systemic RV (129.75 ± 0.12 km s−1) allows its Lyα emission to avoid absorption by the interstellar medium, making it a prime candidate for probing atmospheric escape from HD 60779 b. HD 60779 is also the third brightest host of a Porb > 25 day sub-Neptune with a measured mass and radius, distinguishing it in terms of accessibility to spectroscopic characterization.