  The tidal heating of hypothetical rocky (or terrestrial) extra-solar planets
spans a wide range of values depending on stellar masses and initial orbits.
Tidal heating may be sufficiently large (in many cases, in excess of radiogenic
heating) and long-lived to drive plate tectonics, similar to the Earth's, which
may enhance the planet's habitability. In other cases, excessive tidal heating
may result in Io-like planets with violent volcanism, probably rendering them
unsuitable for life. On water-rich planets, tidal heating may generate
sub-surface oceans analogous to Europa's with similar prospects for
habitability. Tidal heating may enhance the outgassing of volatiles,
contributing to the formation and replenishment of a planet's atmosphere. To
address these issues, we model the tidal heating and evolution of hypothetical
extra-solar terrestrial planets. The results presented here constrain the
orbital and physical properties required for planets to be habitable.
