  Space astrometry is capable of sub-microarcsecond measurements of star
positions. A hundred visits over several years could yield relative astrometric
precision of ~0.1 uas, below the astrometric signature (0.3 uas) of a Sun-Earth
system at a distance of 10 parsecs. We investigate the impact of starspots on
the detectability, via astrometric and radial velocity techniques, of Earthlike
planets orbiting Sunlike stars. We find that for nearby stars, although
starspot noise imposes severe restrictions on detectability by the radial
velocity technique, it does not significantly affect astrometric detectability
of habitable zone planets down to below an Earth mass.
