a1 Cardiff Centre for Astrobiology, Cardiff University, 2 North Road, Cardiff CF10 3DY, UK e-mail: email@example.com
Mechanisms of interstellar panspermia have recently been identified whereby life, wherever it has originated, will disperse throughout the habitable zone of the Galaxy within a few billion years. This re-opens the question of where life originated. The interiors of comets, during their aqueous phase, seem to provide environments no less favourable for the origin of life than that of the early Earth. Their combined mass throughout the Galaxy overwhelms that of suitable terrestrial environments by about 20 powers of ten, while the lifetimes of friendly prebiotic environments within them exceeds that of localized terrestrial regions by another four or five powers of ten. We propose that the totality of comets around G-dwarf Sun-like stars offers an incomparably more probable setting for the origin of life than any that was available on the early Earth.
(Received July 10 2007)
(Accepted October 04 2007)
(Online publication August 06 2007)