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Small black rock-fungi and lichens on the way of Lithopanspermia

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In this 7th session of the internet-based live lectures between Universities and Institutes, Dr Silvano Onofori discusses Cryptoendolithic microbial communities and epilithic lichens that have been considered as appropriate candidates for the scenario of lithopanspermia, which proposes a natural interplanetary exchange of organisms by means of rocks that have been impact ejected from their planet of origin. 



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Lithopanspermia in Star Forming Clusters
Authors:
Fred C. Adams, David N. Spergel

This paper considers the lithopanspermia hypothesis in star forming groups and clusters, where the chances of biological material spreading from one solar system to another is greatly enhanced (relative to the field) due to the close proximity of the systems and lower relative velocities.
These effects more than compensate for the reduced time spent in such crowded environments.
This paper uses 300,000 Monte Carlo scattering calculations to determine the cross sections for rocks to be captured by binaries and provides fitting formulae for other applications.
We assess the odds of transfer as a function of the ejection speed and number of members in the birth aggregate. The odds of any given ejected meteoroid being recaptured by another solar system are relatively low. Because the number of ejected rocks per system can be large, virtually all solar systems are likely to share rocky ejecta with all of the other solar systems in their birth cluster.

The number of ejected rocks that carry living micro organisms is much smaller and less certain, but we estimate that several million rocks can be ejected from a biologically active solar system.

For typical birth environments, the capture of life bearing rocks is expected to occur 10 -- 16,000 times per cluster (under favourable conditions), depending on the ejection speeds.
Only a small fraction of the captured rocks impact the surfaces of terrestrial planets, so that only a few lithopanspermia events are expected (per cluster).


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