  We consider the approach to self-similarity (or dynamical scaling) in
Smoluchowski's equations of coagulation for the solvable kernels $K(x,y)=2$,
$x+y$ and $xy$. In addition to the known self-similar solutions with
exponential tails, there are one-parameter families of solutions with algebraic
decay, whose form is related to heavy-tailed distributions well-known in
probability theory. For K=2 the size distribution is Mittag-Leffler, and for
$K=x+y$ and $K=xy$ it is a power-law rescaling of a maximally skewed
$\alpha$-stable Levy distribution. We characterize completely the domains of
attraction of all self-similar solutions under weak convergence of measures.
Our results are analogous to the classical characterization of stable
distributions in probability theory. The proofs are simple, relying on the
Laplace transform and a fundamental rigidity lemma for scaling limits.
