A Family of Newborn Planets Transiting a Young Solar Analog at 20-30 Myr

Compact, multi-planet systems are one of the defining discoveries of the Kepler mission. These planetary systems are ubiquitous in the galaxy yet much about their nature remains a mystery, including whether they formed in situ and what their architectures were when the protoplanetary disk dispersed. Theoretical models suggest that close-in Kepler planets had radii that were roughly 2 to 10 times larger at the time of disk dispersal. With the recent discoveries of exoplanets transiting young stars (<100 Myr), it is now possible to put these models to the test and study close-in planets at a stage when contraction, cooling, and initial atmospheric loss are still underway. To date, only a few exoplanets have been discovered transiting pre-main sequence stars, all of which are currently single-planet systems. I will discuss the recent detection of four transiting planets larger than 5 Earth radii orbiting within 0.5 AU of a young solar analog aged between 20-30 Myr. The inner planets are larger than Neptune and expected to be actively losing envelope mass through photo-evaporation. The outer planets are both Jupiter-sized and, with separations >0.15 AU, they are expected to be largely shielded from the effects of photo-evaporation. Consequently, the outer planets may be particularly valuable benchmarks, with properties that may more closely reflect the initial conditions of Kepler planets. In a single system, we thus have the opportunity to study proto-Kepler planets across a range of insolation fluxes shortly after the accretion of envelopes and at a time when stellar X-ray emission is near its peak.