Andromeda XVIII

Andromeda XVIII, discovered in 2008, is a dwarf spheroidal galaxy, which is a satellite of the Andromeda Galaxy. It is one of the 14 known dwarf galaxies orbiting M31. It is relatively isolated, being about 1.8 million light-years away. However, for an isolated dwarf galaxy it is also unusually quiescent. This suggests that Andromeda XVIII is a backsplash galaxy, a galaxy that once had a close orbital encounter with a more massive galaxy which stripped it of much of its star-forming matter. However, alternative hypotheses are also possible for Andromeda XVIII.
It was announced in 2010 that the orbiting galaxies lie close to a plane running through M31's center.