GEO and LEO: The Final Frontier for Plutonic FFP Parallax

Abstract

I show that microlens parallaxes, ${\pi }_{\mathrm{E}}$, 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, ${\theta }_{\mathrm{E}}$, from finite-source effects, such ${\pi }_{\mathrm{E}}$ measurements directly yield the FFP mass $M={\theta }_{\mathrm{E}}/\kappa {\pi }_{\mathrm{E}}$ 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 ${\pi }_{\mathrm{E},\pm }$.

15 pages, 3 figures