The minimum mass of detectable planets in protoplanetary discs and the derivation of planetary masses from high resolution observations

TL;DR

This study determines the minimum detectable planet mass in protoplanetary discs using high-resolution infrared and submm observations, providing methods to estimate planetary masses from observed disc structures.

Contribution

It introduces multi-fluid simulations to identify observable signatures of low-mass planets and offers a framework to derive planet masses from disc imaging data.

Findings

Minimum detectable planet mass is approximately 15 Earth masses.

Planets above 20 Earth masses create dust traps and potential disc holes.

Disc features in images can be used to estimate planetary masses.

Abstract

We investigate the minimum planet mass that produces observable signatures in infrared scattered light and submm continuum images and demonstrate how these images can be used to measure planet masses to within a factor of about two. To this end we perform multi-fluid gas and dust simulations of discs containing low mass planets, generating simulated observations at $1.65 \mu$m, $10 \mu$m and $850 \mu$m. We show that the minimum planet mass that produces a detectable signature is $\sim 15 M_\oplus$: this value is strongly dependent on disc temperature and changes slightly with wavelength (favouring the submm). We also confirm previous results that there is a minimum planet mass of $\sim 20 M_\oplus$ that produces a pressure maximum in the disc: only planets above this threshold mass generate a dust trap that can eventually create a hole in the submm dust. Below this mass, planets produce annular enhancements in dust outward of the planet and a reduction in the vicinity of the planet. These features are in steady state and can be understood in terms of variations in the dust radial velocity, imposed by the perturbed gas pressure radial profile, analogous to a traffic jam. We also show how planet masses can be derived from structure in scattered light and sub-mm images. We emphasise that simulations with dust need to be run over thousands of planetary orbits so as to allow the gas profile to achieve a steady state and caution against the estimation of planet masses using gas only simulations.