Named simply Mone, Ottansey's sole moon is about 4 times the mass of Luna and is only 85% of the distance from Terra to Luna. Its angular diameter is 3.27 degrees, or nearly seven times that of Luna from Terra. Mone raises tides on Ottansey about 5.5 times the size of Terran tides. These occur every 17 hours 3 minutes 54 seconds.
Mone is tidal-locked, and thus presents always the same face to Ottansey. The eastern limb is scarred by an emormous crater, which was formed when Ottansey was settled and Mone's revolutionary period was slowed to make it exactly 1/20 of the Ottansey yere.
Mone resembles Mercury in composition, size, mass, and general appearance.