Debiasing the Minimum-Mass Extrasolar Nebula: Planet Multiplicity and the Diversity of Solid Density Profiles

A foundational idea in the theory of in situ planet formation is the “minimum mass extrasolar nebula” (MMEN), a power-law profile for the surface density of disk solids that is necessary to form the planets we see in their present locations. While the MMEN framework is intuitively simple, it continues to be debated whether most exoplanetary systems fit a universal disk template. Previous studies have relied on simplistic treatments for detection biases and the exoplanet mass-radius relationship to construct the MMEN from the Kepler planet catalog. The recent development of detailed forward models for the Kepler mission has enabled unprecedented inferences on the intrinsic population of inner planetary systems from the observed population, leading to advanced statistical models, such as the “maximum AMD model” that captures the underlying architectures and correlations in multi-planet systems. Here, we use simulated catalogs from this model to reconstruct the MMEN. Fitting a power-law relation for the solid surface density as a function of semi-major axis to each individual multi-planet system results in a diverse distribution of disk profiles. Our approach allows us to account for the role of non-transiting and undetected planets in altering the MMEN; we find that while transit observations do not tend to bias the inferred median power-law slope, they can lead to both over- and under-estimated normalizations for the disk density and thus significantly broaden the inferred distribution for MMEN mass. We use our model to explore how the MMEN varies with planet multiplicity and prescriptions for the feeding zone width, and discuss implications for planet formation.