The CO-Fuelled Time Machine: Tracing Birth Conditions and Terrestrial Planet Formation Outcomes in HD 163296 through Pebble Drift-induced CO Enhancements

TL;DR

This paper introduces a novel method to infer the initial conditions of protoplanetary discs by analyzing CO enhancements caused by pebble drift, providing insights into planet formation around HD 163296.

Contribution

The study combines MCMC sampling with a fast radial drift model to retrieve birth disc properties from observed CO enhancements, advancing understanding of planet-forming environments.

Findings

Estimated birth gas mass of the disc: log10(M_disc/M_sun) ≈ -0.64

Derived characteristic radius of the disc: log10(r_c/AU) ≈ 2.30

Dust grains must be fragile with fragmentation velocity ~100 cm/s

Abstract

The architecture and composition of planetary systems are thought to be strongly influenced by the transport and delivery of dust and volatiles via ices on pebbles during the planet formation phase in protoplanetary discs. Understanding these transport mechanisms is crucial in building a comprehensive picture of planet formation, including material and chemical budget; constraining the birth properties of these discs is a key step in this process. We present a novel method of retrieving such properties by studying the transport of icy pebbles in the context of an observed gas-phase CO enhancement within the CO snowline in the protoplanetary disc around HD 163296. We combine Markov Chain Monte Carlo (MCMC) sampling with a fast model of radial drift to determine the birth gas mass and characteristic radius of the disc, and compare our results against observations and models in the literature; we find the birth-condition disc gas mass to be $\log_{10}(M_{\rm{disc}}/M_{\odot})=-0.64^{+0.19}_{-0.24}$ and the characteristic radius to be $\log_{10}(r_{\rm{c}}/\rm{AU})=2.30^{+0.45}_{-0.46}$. We additionally determine that dust grains must be `fragile' ($v_{f}=100~\mathrm{cms}^{-1}$) to retain enough dust to match current dust mass observations, with our lowest fragmentation velocity model providing a current-age dust mass of $\rm{M_{dust}}=662^{+518}_{-278} \rm{M_{\oplus}}$ based on the retrieved birth conditions. Using our retrieved birth conditions, we extend our simulations to mass of material reaching the water snowline in the inner disc, where terrestrial and super-Earth planets may be forming, and speculate on the nature of these exoplanets.