ON THE FEASIBILITY OF CHARACTERIZING FREE-FLOATING PLANETS WITH CURRENT AND FUTURE SPACE-BASED MICROLENSING SURVEYS

Abstract

Simultaneous space- and ground-based microlensing surveys, such as K2 's Campaign 9 ( K2 C9) and WFIRST , facilitate measuring the masses and distances of free-floating planet (FFP) candidates, which are identified as single-lens events with timescales that are of the order of 1 day. Measuring the mass and distance of an FFP lens requires determining the size of the source star ρ , measuring the microlens parallax , and using high-resolution imaging to search for the lens flux from a possible host star. Here we investigate the accessible parameter space for each of these components considering different satellites for a range of FFP masses, Galactic distances, and source star properties. We find that at the beginning of K2 C9, when its projected separation from the Earth is ≲0.2 au, it will be able to measure for Jupiter-mass FFP candidates at distances larger than ∼2 kpc and to Earth-mass lenses at ∼8 kpc. At the end of K2 C9, when = 0.81 au, it is sensitive to planetary-mass lenses for distances ≳3.5 kpc, and even then only to those with mass ≳ M Jup . From lens flux constraints we find that it will be possible to exclude hosts down to the deuterium-burning limit for events within ∼2 kpc. This indicates that the ability to characterize FFPs detected during K2 C9 is optimized for events occurring toward the beginning of the campaign. WFIRST , on the other hand, will be able to detect and characterize FFP masses down to or below super-Earths throughout the Galaxy during its entire microlensing survey.