  The atmospheres of close-in extrasolar planets absorb most of the incident
stellar radiation, advect this energy, then reradiate photons in preferential
directions. Those photons carry away momentum, applying a force on the planet.
Here we evaluate the resulting secular changes to the orbit, known as the
Yarkovsky effect. For known transiting planets, typical fractional changes in
semi-major axis are about 1% over their lifetime, but could be up to ~5% for
close-in planets like OGLE-TR-56b or inflated planets like TrES-4. We discuss
the origin of the correlation between semi-major axis and surface gravity of
transiting planets in terms of various physical processes, finding that
radiative thrusters are too weak by about a factor of 10 to establish the lower
boundary that causes the correlation.
