Comets in other planetary systems?
Comets in our solar system appear to have provided a bridge between the cold, volatile-rich outer solar system, and the warm, but volatile-poor inner solar system.  Excluding tidal and possible extinct radionuclide heating sources, only in the inner solar system are temperatures high enough for liquid water, and therefore life as we know it, to exist for times comparable to the age of the solar system.  Comets may have been crucial for providing biogenic volatiles and perhaps organic molecules to this warm environment.  It is therefore interesting from an exobiological point of view to ask if comets exist in other planetary systems.  Most attempts to detect comets around other stars or in interstellar space have failed.  However, there is growing spectroscopic evidence for comet-like bodies orbiting the star Beta Pictoris.
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Laboratory for Extraterrestrial Physics, NASA Goddard Space Flight Center, Greenbelt, MD 20771, USA.
D055580:Astronomical Phenomena; D001256:Astronomy; D019418:Evolution, Chemical; D018559:Exobiology; D005118:Extraterrestrial Environment; D019110:Meteoroids; D008962:Models, Theoretical; D016082:Solar System