  We have shown that Earth-mass planets could survive in variously restricted
regions of the habitable zones (HZs) of most of a sample of nine of the 93
main-sequence exoplanetary systems confirmed by May 2003. In a preliminary
extrapolation of our results to the other systems, we estimate that roughly a
third of the 93 systems might be able to have Earth-mass planets in stable,
confined orbits somewhere in their HZs. Clearly, these systems should be high
on the target list for exploration for terrestrial planets. We have reached
this conclusion by launching putative Earth-mass planets in various orbits and
following their fate with a mixed-variable symplectic integrator.
