<i>Kepler K2</i>Campaign 9 – II. First space-based discovery of an exoplanet using microlensing

ABSTRACT We present K2-2016-BLG-0005Lb, a densely sampled, planetary binary caustic-crossing microlensing event found from blind search of data gathered Campaign 9 the Kepler K2 mission (K2C9). K2-2016-BLG-0005Lb is first bound exoplanet discovered space-based data. The has caustic entry and exit points that are resolved in K2C9 data, enabling lens-source relative proper motion to be measured. have fitted microlens model simultaneous observations multiple ground-based surveys. Whilst only sparsely sample caustic, they provide clear detection parallax allows us break completely mass-position-velocity degeneracy measure planet’s mass directly. find host 0.58 ± 0.04 M⊙ 1.1 0.1 MJ. system lies at distance 5.2 0.2 kpc Earth towards Galactic bulge, more than twice previous most distant planet by Kepler. sky-projected separation its 4.2 0.3 au which, for circular orbits, deprojects $a = 4.4^{+1.9}_{-0.4}$ orbital period $P 13^{+9}_{-2}$ yr. This makes close Jupiter analogue orbiting low-mass star. According current formation models, this very threshold below which Jupiters not expected form. Upcoming surveys NASA’s Nancy Grace Roman Space Telescope and, possibly, ESA’s Euclid mission, will demanding tests models.