Motivated by Smale's work in dynamics, the following questions are studied and answered: (1) Which 3-manifolds admit an automorphism whose non-wandering set consists of Smale solenoids? (2) Which 3-manifolds admit an automorphism having a knotted Smale solenoid as attractor? As a consequence of (2), every solenoind that appears as an attractor of a homeomorphism of $R^3$ is UNknotted.