Masses for Free-Floating Planets and Dwarf Planets

TL;DR

This paper proposes a method using dual observatories to measure masses and distances of free-floating planets and dwarf planets through microlensing, enabling insights into planetary system formation.

Contribution

It introduces a novel observational strategy combining existing and proposed telescopes to measure free-floating planets' properties across different mass ranges.

Findings

130 measurements over four years for FFPs down to 0.7 Earth masses.

Potential to measure sub-Moon mass objects and distinguish dwarf planets.

Feasible with current and near-future telescope configurations.

Abstract

The mass and distance functions of free-floating planets (FFPs) would give major insights into the formation and evolution of planetary systems, including any systematic differences between those in the disk and bulge. We show that the only way to measure the mass and distance of individual FFPs over a broad range of distances is to observe them simultaneously from two observatories separated by $D\sim {\cal O}(0.01\,AU)$ (to measure their microlens parallax $\pi_{\rm E}$) and to focus on the finite-source point-lens (FSPL) events (which yield the Einstein radius $\theta_{\rm E}$). By combining the existing KMTNet 3-telescope observatory with a 0.3m $4\,{\rm deg}^2$ telescope at L2, of order 130 such measurements could be made over four years, down to about $M\sim 6\,M_\oplus$ for bulge FFPs and $M\sim 0.7\,M_\oplus$ for disk FFPs. The same experiment would return masses and distances for many bound planetary systems. A more ambitious experiment, with two 0.5m satellites (one at L2 and the other nearer Earth) and similar camera layout but in the infrared, could measure masses and distances of sub-Moon mass objects, and thereby probe (and distinguish between) genuine sub-Moon FFPs and sub-Moon ``dwarf planets'' in exo-Kuiper Belts and exo-Oort Clouds.