Evolutionary processes transpiring in the stages of lithopanspermia
Résumé
Lithopanspermia is the theory that proposes the natural exchange of organisms between solar system bodies due to asteroidal or cometary impactors. Research not only studies the physics of the stages themselves, but also the survival probabilities of life in each of these. However, although life is the primary factor of interest in lithopanspermia, this life is mainly treated as a passive cargo. Life, however, does not merely passively receive an onslaught from stressful surroundings, it reacts. Thus, planetary ejection, interplanetary transport, and planetary entry are just the first 3 factors in the equation. The other factors are the quality, quantity, and evolutionary strategy of the transported organisms. Thus, it may be the case that a reduction in quantity in stage 1 will increase the quality towards a second stress challenge in stage 3, by increasing the frequency of robust genotypes. Thus, robustness towards a stressor may in fact be higher in the surviving bacterial population at the end of transport, in stage 3, than at its beginning, in stage 1. Thus, the stages of lithopanspermia can themselves act as facilitators of evolutionary processes that enhance the ability of the collected organisms to survive e.g. pressure and heat shock. Thus, the multiple abiotic pressures the population encounters through the 3 stages can potentially develop very robust bacteria with enhanced survival capacities considerably higher than otherwise expected. The analysis details a possible, but probably rare, possibility. However, next to lithopanspermia there is also the potential space craft mediated panspermia. The analogous stages in a space craft may provide a greater likelihood towards increasing the stress tolerance of hitch hiking organisms. Furthermore, missions that seek life elsewhere will frequently be sent to places where it has been assumed that there may be life as we know it. Thus, not only can we bring terrestrial organisms where they are potentially more likely to survive, but may also have given them a boost to their invasive potential along the way. The analysis highlights further demands planetary protection protocols need to implement, as well as providing a framework for analyzes of ecological scenarios regarding transmissions of life, natural or artificial, between worlds in a solar system.
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