WFIRST and EUCLID: enabling the microlensing parallax measurement from space

The Wide Field Infrared Survey Telescope (WFIRST) is expected to detect hundreds of free-floating planets, but it will not be able to measure their masses. However, simultaneous microlensing observations by both Euclid and WFIRST spacecraft, separated by ~ 100, 000 km in orbits around the Sun-Earth L2 Lagrange point, will enable measurements of microlensing parallax for low-mass lenses such as free-floating planets. Using simple Fisher matrix estimates of the parallax measurement uncertainties, we show that high-cadence observations by Euclid could be used to measure ~ 1 free-floating planet microlens parallax per 6 days of simultaneous Euclid observations. Accounting for Euclid's pointing constraints, it could therefore potentially measure ~ 20 free-floating planet parallaxes with 120 days of observations split equally between Euclid's main mission and an extended mission, with a potential to increase this number if spacecraft pointing constraints can be relaxed after the end of the main mission. These Euclid observations would also provide additional mass measurements or cross-checks for larger numbers of WFIRST's bound planets, among other benefits to several science cases.