The stability of the orbits of terrestrial planets in the habitable zones of known exoplanetary systems

We have investigated whether terrestrial planets can exist in orbits in kno wn exoplanetary systems such that life could have emerged on those planets. Four contrasting systems have been examined in which giant planets have be en detected. Mixed-variable symplectic numerical integration has been used to investigate the orbits of putative terrestrial planets within the habita ble zone of each system (the range of distances from the star within which water at the surface of a terrestrial planet would be in the liquid phase). We have shown that Rho CrB and 47 UMa could have terrestrial planets in or bits that remain confined to their habitable zones for biologically signifi cant lengths of time. We have also shown that the Gliese 876 and Ups And sy stems are very unlikely to have such orbits.