  We study theoretically the dynamics of two-component Bose-Einstein
condensates in two dimensions, which admit topological excitations related to
the Skyrmions of nuclear physics. We show that there exists a branch of
uniformly propagating solitary waves characterised by a conserved momentum.
These excitations exhibit a cross-over from spatially extended spin-wave states
at low momentum to a localised "spin-wave droplet" at intermediate momentum; at
still higher momentum, the configuration evolves continuously into a
Skyrmion-antiSkyrmion pair. We discuss how these solitary waves can be
generated and studied in experiment.
