The Collaborative International Dictionary of English v.0.48:

astrobiology \astrobiology\ n.
   exobiology; -- not used technically.

   Syn: exobiology.
        [PJC]

WordNet (r) 3.0 (2006):

astrobiology
    n 1: the branch of biology concerned with the effects of outer
         space on living organisms and the search for
         extraterrestrial life [syn: exobiology, space biology,
         astrobiology]