  Planetary migration is essential to explain the observed mass-period relation
for exoplanets. Without some stopping mechanism, the tidal, resonant
interaction between planets and their gaseous disc generally causes the planets
to migrate inward so efficiently that they plunge into the host star within the
gaseous disc lifetime ($\sim $ 1-3 Myrs). We investigate planetary migration by
analytically calculating the migration rate and time within self-consistently
computed, radiatively heated discs around M stars in which the effects of dust
settling are included. We show that dust settling lowers the disc temperature
and raises the gas density in the mid-plane. This inescapable evolution of disc
structure speeds up type I planetary migration for lower mass bodies by up to a
factor of about 2. We also examine the effects of dust settling on the
gap-opening mass and type II migration, and find that the gap-opening mass is
reduced by a factor of 2 and type II migration becomes slower by a factor of 2.
While dust settling can somewhat alleviate the problem of planetary migration
for more massive planets, the more rapid migration of low mass planets and
planetary cores requires a robust slowing mechanism.
