Evidently, M102 is the last possibly `missing', or doubty, Messier object. This means that two opinions on the identity of this object are common:

1. M102 may be a duplication of the Spiralna galaksija - Spiral Galaxy M101 (NGC 5457) in ursa Major, due to an error of either the catalog author Messier, or its `discoverer' Mechain.
2. M102 may be the Lenticular Galaxy NGC 5866 in draco, also sometimes called the Spindle Galaxy, as Messier's catalog description indicates, together with the position he added later by hand.

Some details on this topic are discussed here.