Microlensing Detections of Moons of Exoplanets

TL;DR

This paper explores the potential of microlensing to detect moons of exoplanets, identifying optimal separation ranges and comparing detection capabilities with transit methods.

Contribution

It characterizes microlensing signals of exomoons, establishing detection ranges based on planet-moon separation and comparing with other detection techniques.

Findings

Satellite signals are detectable when the planet-moon separation exceeds the Einstein radius.

Satellite signals tend to have the same sign as planetary signals due to lensing effects.

Optimal detection ranges vary by planet mass, e.g., 0.05-0.24 AU for Jupiter-mass planets.

Abstract

We investigate the characteristic of microlensing signals of Earth-like moons orbiting ice-giant planets. From this, we find that non-negligible satellite signals occur when the planet-moon separation is similar to or greater than the Einstein radius of the planet. We find that the satellite signal does not diminish with the increase of the planet-moon separation beyond the Einstein radius of the planet unlike the planetary signal which vanishes when the planet is located well beyond the Einstein radius of the star. We also find that the satellite signal tends to have the same sign as that of the planetary signal. These tendencies are caused by the lensing effect of the star on the moon in addition to the effect of the planet. We determine the range of satellite separations where the microlensing technique is optimized for the detections of moons. By setting an upper limit as the angle-average of the projected Hill radius and a lower limit as the half of the Einstein radius of the planet, we find that the microlensing method would be sensitive to moons with projected separations from the planet of $0.05 {\rm AU} \lesssim d_{\rm p} \lesssim 0.24 {\rm AU}$ for a Jupiter-mass planet, $0.03 {\rm AU}\lesssim d_{\rm p} \lesssim 0.17 {\rm AU}$ for a Saturn-mass planet, and $0.01 {\rm AU} \lesssim d_{\rm p} \lesssim 0.08 {\rm AU}$ for a Uranus-mass planet. We compare the characteristics of the moons to be detected by the microlensing and transit techniques