Kepler Microlens Planets and Parallaxes

TL;DR

Kepler can be repurposed to detect and characterize cool, outer solar system planets via microlensing, especially when combined with ground-based surveys, enabling detailed mass, distance, and population studies.

Contribution

This paper proposes using Kepler for microlensing planet detection and parallax measurement, expanding its capabilities beyond primary transit searches.

Findings

Kepler could detect microlensing planets in the Galactic bulge.

Combining Kepler with ground surveys allows mass and distance measurements for many planets.

The survey would also identify brown-dwarf binaries and probe the stellar mass function.

Abstract

Kepler's quest for other Earths need not end just yet: it remains capable of characterizing cool Earth-mass planets by microlensing, even given its degraded pointing control. If Kepler were pointed at the Galactic bulge, it could conduct a search for microlensing planets that would be virtually non-overlapping with ground-based surveys. More important, by combining Kepler observations with current ground-based surveys, one could measure the "microlens parallax" \pi_E for a large fraction of the known microlensing events. Such parallax measurements would yield mass and distance determinations for the great majority of microlensing planets, enabling much more precise study of the planet distributions as functions of planet and host mass, planet-host separation, and Galactic position (particularly bulge vs. disk). In addition, rare systems (such as planets orbiting brown dwarfs or black holes) that are presently lost in the noise would be clearly identified. In contrast to Kepler's current primary hunting ground of close-in planets, its microlensing planets would be in the cool outer parts of solar systems, generally beyond the snow line. The same survey would yield a spectacular catalog of brown-dwarf binaries, probe the stellar mass function in a unique way, and still have plenty of time available for asteroseismology targets.