  Self-propulsion of a Janus droplet in a solution of surfactant, which reacts
on a half of a drop surface, is studied theoretically. The droplet acts as a
catalytic motor creating a concentration gradient, which generates its
surface-tension-driven motion; the self-propulsion speed is rather high, $60\;
{\rm \mu m/s}$ and more. This catalytic motor has several advantages over other
micromotors: simple manufacturing, easily attained neutral buoyancy. In
contrast to a single-fluid droplet, which demonstrates a self-propulsion as a
result of symmetry breaking instability, for Janus one no stability threshold
exists; hence, the droplet radius can be scaled down to micrometers.
  The paper was finalized and submitted by Denis S. Goldobin after Sergey
Sklyaev had sadly passed away on June 2, 2014.

Fluid Dynamics;Soft Condensed Matter