# Microlensing Results Challenge the Core Accretion Runaway Growth Scenario for Gas Giants

## TL;DR

Microlensing observations challenge core accretion models by showing more intermediate-mass gas giants than predicted, suggesting alternative formation processes or environmental variations.

## Contribution

This study compares microlensing data with core accretion models, revealing a significant discrepancy in predicted and observed planet mass distributions.

## Key findings

- Microlensing detects more intermediate-mass gas giants than models predict.
- Core accretion models underestimate planets with mass ratios of 10^{-4} to 4×10^{-4}.
- Discrepancies suggest alternative formation processes or environmental factors.

## Abstract

We compare the planet-to-star mass-ratio distribution measured by gravitational microlensing to core accretion theory predictions from population synthesis models. The core accretion theory's runaway gas accretion process predicts a dearth of intermediate-mass giant planets that is not seen in the microlensing results. In particular, the models predict $\sim10\,\times$ fewer planets at mass ratios of $10^{-4} \leq q \leq 4 \times 10^{-4}$ than inferred from microlensing observations. This tension implies that gas giant formation may involve processes that have hitherto been overlooked by existing core accretion models or that the planet-forming environment varies considerably as a function of host-star mass. Variation from the usual assumptions for the protoplanetary disk viscosity and thickness could reduce this discrepancy, but such changes might conflict with microlensing results at larger or smaller mass ratios, or with other observations. The resolution of this discrepancy may have important implications for planetary habitability because it has been suggested that the runaway gas accretion process may have triggered the delivery of water to our inner solar system. So, an understanding of giant planet formation may help us to determine the occurrence rate of habitable planets.