The Occurrence-weighted Median Planets Discovered by Transit Surveys Orbiting Solar-type Stars and Their Implications for Planet Formation and Evolution

Since planet occurrence and primordial atmospheric retention probability increase with period, the occurrence-weighted median planets discovered by transit surveys may bear little resemblance to low-occurrence, short-period sculpted escape ordinarily used calibrate mass--radius relations formation models. An relation for low-mass so far orbiting solar-type stars requires both Earth-mass Neptune-mass have a few percent of their masses in hydrogen/helium (H/He) atmospheres. Unlike Earth that finished forming long after protosolar nebula was dissipated, these must formed early systems' histories. The existence significant H/He atmospheres around confirms an important prediction core-accretion model formation. It also implies core $M_{\text{c}}$ range $2~M_{\oplus}\lesssim M_{\text{c}}\lesssim 8~M_{\oplus}$ can retain If is driven photoevaporation due extreme ultraviolet (EUV) flux, then our observation reduction fraction incident EUV flux converted into work usually assumed driven, large Bond albedos. In contrast Uranus Neptune at least 10% atmospheres, are poor. implication they experienced collisions or much shorter-lived and/or hotter parts parent protoplanetary disks than Neptune's location nebula.