Quote:
Originally Posted by eburacum45
The number of unknowns are very high. If abiogenesis occurs frequently and early while the stars are still in the cluster then the rate of cross-infection increases. Additionally the cluster can act as a net to catch wandering life-bearing rocks; it seems possible that once a rock wanders into a tightly packed cluster and starts off a process of lithopanspermia in that cluster, several worlds might be infected in the heavy bombardment phases of planetary development in each system. This would drive up the frequency of cross-infection, if the process happens at all.
On the downside there is no guarantee that a lifebearing rock will sucessfully infect the planet it fall upon; the environment in some larger clusters is dangerous because of the hot, bright stars which are prone to explode, and life may quickly die out on many or most worlds even if a biosphere forms.
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The cluster they describe has 1000 stars within 1 parsec, this enables them to ignore the transit times between stars. Nonetheless life still requires ~100Myr for ejection and arrival. Once the rock is moving outside the cluster the time would get ridiculously huge, maybe it wouldn't be able to keep up with the expansion of space.
So even in the most optimistic lithopanspermic scenario the probability of a single successful transfer event is 1 multiplied by the probability of a single occurrence of newly evolved life surviving heavy bombardment, acceleration to 5km/s, 100myr+ in deep space of a stellar nursery, impact, and then thriving on whatever object it happens to land.