Kepler-1625b I
Kepler 1625b I, a possible moon of exoplanet Kepler-1625b, may be the first exomoon ever discovered, and was first indicated after preliminary observations by the Kepler Space Telescope. A more thorough observing campaign by the Hubble Space Telescope took place in October 2017, ultimately leading to a discovery paper published in "Science Advances" in early October 2018. Studies related to the discovery of this moon suggest that the host exoplanet is up to several Jupiter masses in size, and the moon is thought to be approximately the mass of Neptune. There is a possibility that the large exomoon may have a moon itself, called a moonmoon. Kepler-1625b I may be habitable, considering the host planet has an equilibrium temperature of.
However, a reanalysis of the data published in April 2019 concluded that the data was fit better by a planet-only model. According to this study, the discrepancy was an artifact of the data reduction, and Kepler-1625b I likely does not exist.
