Mann, Andrew W., Johnson, Marshall C., Vanderburg, Andrew, Kraus, Adam L., Rizzuto, Aaron C., Wood, Mackenna L., Bush, Jonathan L., Rockcliffe, Keighley, Newton, Elisabeth R., Latham, David W., Mamajek, Eric E., Zhou, George, Quinn, Samuel N., Thao, Pa Chia, Benatti, Serena, Cosentino, Rosario, Desidera, Silvano, Harutyunyan, Avet, Lovis, Christophe, Mortier, Annelies, Pepe, Francesco A., Poretti, Ennio, Wilson, Thomas G., Kristiansen, Martti H., Gagliano, Robert et al. 2020. "TESS Hunt for Young and Maturing Exoplanets (THYME). III. A Two-planet System in the 400 Myr Ursa Major Group." The Astronomical Journal, 160 179. https://doi.org/10.3847/1538-3881/abae64.
Exoplanets can evolve significantly between birth and maturity, as their atmospheres, orbits, and structures are shaped by their environment. Young planets (⊕ and 2.67 ± 0.12 R⊕, the orbital periods are 7.11 and 20.55 days, and the orbital eccentricities are lower than about 0.2. Using High Accuracy Radial velocity Planet Searcher for the Northern hemisphere velocities, we measure the Rossiter-McLaughlin signal of the inner planet, demonstrating that the orbit is prograde. Since the host star is bright (V = 6.9), both planets are amenable to transmission spectroscopy, radial velocity measurements of their masses, and more precise determination of the stellar obliquity. This system is therefore poised to play an important role in our understanding of planetary system evolution in the first billion years after formation.
