  We study the supersymmetric solutions of 11-dimensional supergravity with a
factor of $AdS_2$ made of M2-branes. Such solutions can provide gravity duals
of superconformal quantum mechanics, or through double Wick rotation, the
generic bubbling geometry of M-theory which are 1/16-BPS. We show that, when
the internal manifold is compact, it should take the form of a warped
U(1)-fibration over an 8-dimensional Kahler space.
