# Connecting HL Tau to the Observed Exoplanet Sample

## TL;DR

This study uses N-body simulations to connect initial planet formation conditions observed in HL Tau with the diverse exoplanet populations, including eccentricities, hot Jupiters, and free-floating planets.

## Contribution

It demonstrates that HL Tau's initial planetary conditions can naturally produce observed exoplanet characteristics and offers predictions for mutual inclination distributions.

## Key findings

- Reproduces the eccentricity distribution of giant exoplanets.
- Matches the observed rate of hot Jupiters around FGK stars.
- Predicts a broad mutual inclination distribution for future observations.

## Abstract

The Atacama Large Millimeter/submilimeter Array (ALMA) recently revealed a set of nearly concentric gaps in the protoplanetary disk surrounding the young star HL Tau. If these are carved by forming gas giants, this provides the first set of orbital initial conditions for planets as they emerge from their birth disks. Using N-body integrations, we have followed the evolution of the system for 5 Gyr to explore the possible outcomes. We find that HL Tau initial conditions scaled down to the size of typically observed exoplanet orbits naturally produce several populations in the observed exoplanet sample. First, for a plausible range of planetary masses, we can match the observed eccentricity distribution of dynamically excited radial velocity giant planets with eccentricities $>$ 0.2. Second, we roughly obtain the observed rate of hot Jupiters around FGK stars. Finally, we obtain a large efficiency of planetary ejections of $\approx 2$ per HL Tau-like system, but the small fraction of stars observed to host giant planets makes it hard to match the rate of free-floating planets inferred from microlensing observations. In view of upcoming GAIA results, we also provide predictions for the expected mutual inclination distribution, which is significantly broader than the absolute inclination distributions typically considered by previous studies.