California-Kepler Survey. IX. Revisiting the Minimum-mass Extrasolar Nebula with Precise Stellar Parameters

Abstract

We investigate a possible correlation between the solid surface density Σ of the minimum-mass extrasolar nebula (MMEN) and the host star mass M★ and metallicity [Fe/H]. Leveraging on the precise host star properties from the California-Kepler Survey (CKS), we found that Σ= 50⁺³³₋₂₀ g cm ⁻² (a/1 au)^(−1.75±0.07) (M★/M⊙)^(1.04±0.22) 10^(0.22±0.05[Fe/H]) for Kepler-like systems (1–4R⊕; a < 1 au). The strong M★ dependence is reminiscent of previous dust continuum results that the solid disk mass scales with M★. The weaker [Fe/H] dependence shows that sub-Neptune planets, unlike giant planets, form readily in lower metallicity environment. The innermost region (a < 0.1 au) of an MMEN maintains a smooth profile despite a steep decline of planet occurrence rate: a result that favors the truncation of disks by corotating magnetospheres with a range of rotation periods, rather than the sublimation of dust. The Σ of Kepler multitransiting systems shows a much stronger correlation with M★ and [Fe/H] than singles. This suggests that the dynamically hot evolution that produced single systems also partially removed the memory of formation in disks. Radial-velocity planets yielded a MMEN very similar to CKS planets; transit-timing-variation planets' postulated convergent migration history is supported by their poorly constrained MMEN. We found that lower mass stars have a higher efficiency of forming/retaining planets: for Sun-like stars, about 20% of the solid mass within ~1 au are converted/preserved as sub-Neptunes, compared to 70% for late-K to early-M stars. This may be due to the lower binary fraction, lower giant-planet occurrence, or the longer disk lifetime of lower mass stars.