Biology
Scientific paper
Feb 2004
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2004mnras.348...46n&link_type=abstract
Monthly Notices of the Royal Astronomical Society, Volume 348, Issue 1, pp. 46-51.
Biology
24
Astrobiology, Comets: General, Interplanetary Medium, Ism: Clouds
Scientific paper
Metre-sized boulders ejected from the Earth by large impacts are destroyed through collisions and erosion by impacting zodiacal cloud dust particles. The time-scale for such disintegration in a dense zodiacal cloud may be <~ 104 yr. Once reduced to a critical size, the particles are rapidly ejected from the Solar system by radiation pressure. The critical size for ejection is of the order of a micron, large enough to protect groups of micro-organisms within them from solar ultraviolet irradiation. Such life-bearing particles are ejected at a mean rate of ~ 1020 per million years. During passages of the Solar system through or close to dense molecular clouds, a significant proportion of the particles may be incorporated into protoplanetary systems and protected from cosmic rays within growing planetesimals. The specific number density of micro-organisms so deposited is highest in small, dense molecular clouds. On the assumption that this ejection mechanism is common in other planetary systems environmentally capable of supporting life, a `chain reaction' may seed the disc of the Galaxy within a few billion years. In that case it is unlikely that life originated on Earth.
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