Solar systems with life-bearing planets are, so far, unique.  There is only one.  But they would be rare anyway, if they are dependent on the presence of asteroid belts of just the right mass, according to two US astronomers.

Rebecca Martin, a NASA Sagan Fellow from the University of Colorado and astronomer Mario Livio of the Space Telescope Science Institute in Baltimore suggest that the size and location of an asteroid belt, shaped by the evolution of the Sun's protoplanetary disk and by the gravitational influence of a nearby giant Jupiter-like planet, may determine whether complex life could evolve on an Earth-like planet. 

So asteroids aren't just a nuisance? They propose instead that asteroid collisions with planets may provide a boost to the birth and evolution of complex life, and might have here - by delivering water and organic compounds to the early Earth. According to the concept of punctuated equilibrium, occasional asteroid impacts might accelerate the rate of biological evolution by disrupting a planet's environment to the point where species must try new adaptation strategies.

The astronomers' theoretical model and archival observations of extrasolar Jupiter-sized planets and debris disks around young stars led
Martin, the study's lead author, to conclude: "Our study shows that only a tiny fraction of planetary systems observed to date seem to have giant planets in the right location to produce an asteroid belt of the appropriate size, offering the potential for life on a nearby rocky planet. Our study suggests that our solar system may be rather special."

Three possible scenarios for the evolution of asteroid belts. In the top panel, a Jupiter-size planet migrates through the asteroid belt, scattering material and inhibiting the formation of life on planets. The second scenario shows our solar-system model: a Jupiter-size planet that moves slightly inward but is just outside the asteroid belt. In the third illustration, a large planet does not migrate at all, creating a massive asteroid belt. Material from the hefty asteroid belt would bombard planets, possibly preventing life from evolving. Illustration Credit: NASA, ESA, and A. Feild (STScI). Science Credit: NASA, ESA, R. Martin and M. Livio (STScI)








Citation: Rebecca G. Martin and Mario Livio. 'On the formation and evolution of asteroid belts and their potential significance for life', Monthly Notices of the Royal Astronomical Society: Letters DOI: 10.1093/mnrasl/sls003 (free to read)