Kepler-1625b

In July 2017, researchers found signs of a Neptune-sized exomoon (a moon in another solar system) orbiting Kepler-1625b using archival Kepler Mission data.

[5][6] In October 2018, researchers using the Hubble Space Telescope published new observations of the star Kepler-1625 which revealed two independent lines of evidence indicative of a large exomoon Kepler-1625b I.

[3] The study concluded that the exomoon hypothesis is the simplest and best explanation for the available observations, though warned that it is difficult to assign a precise probability to its reality and urged follow-up analyses.

[11][3] In February 2019, a reanalysis of the combined Kepler and Hubble observations recovered both a moon-like dip and similar transit timing variation signal.

[8] However, the authors suggested that the data could also be explained by an inclined hot-Jupiter in the same system that has gone previously undetected, which could be tested using future Doppler spectroscopy radial velocity measurements.