GEO and LEO: The Final Frontier for Plutonic FFP Parallax

TL;DR

This paper proposes a method to measure the masses of free-floating planets, including Pluto-sized ones, using combined observations from GEO and LEO or ground-based observatories, enhancing microlensing parallax measurements.

Contribution

It introduces a novel approach to derive microlens parallaxes for low-mass free-floating planets by combining satellite and ground-based observations, enabling precise mass measurements.

Findings

GEO and LEO observations can measure FFP masses down to Pluto size.

Earth-GEO and Earth-L2 observations complement each other for different FFP mass ranges.

Methods are discussed to resolve the two-fold degeneracy in parallax measurements.

Abstract

I show that microlens parallaxes, $\pi_{\rm E}$, can be derived for free-floating planets (FFPs) with masses down to that of Pluto, by combining observations from a satellite in geosynchronous (GEO) orbit with another observatory that is on or near Earth's surface, i.e., either ground-based or in low Earth orbit (LEO). Because these low-mass FFPs typically have measurements of the angular Einstein radius, $\theta_{\rm E}$, from finite-source effects, such $\pi_{\rm E}$ measurements directly yield the FFP mass $M=\theta_{\rm E}/\kappa \pi_{\rm E}$ where $\kappa$ is a physical constant. Such Earth-GEO measurements almost perfectly complement Earth-L2 measurements, which extend to higher FFP mass and greater FFP distance. LEO-only observations can yield mass measurement at even smaller FFP mass and nearer FFP distances. I discuss methods for breaking the Refsdal (1966) two-fold degeneracy in $\pi_{{\rm E},\pm}$.