David Much, et al., report that attention has been given in the literature to the effects of astrophysical events on human and land-based life. However, little has been discussed on the resilience of life itself. In this paper they instead explore the statistics of events that completely sterilize an Earth-like planet with planet radii in the range 0.5 to 1.5 that of the Earth. In this analysis we have considered only direct effects of astrophysical events such as the direct boiling of oceans; however such events could serve as a trigger for a second change. An example of this is the runaway greenhouse effect in which a less energetic event could evaporate a fraction of the ocean, which in turn leads to increased temperatures. Such an occurrence would have a lower threshold energy, as total evaporation of the oceans is no longer necessary; however the precise details of such an event are not known. As an upper bound, we can presume that this would have to increase global temperatures by a larger amount than seasonal variations and changes in solar output. In essence this would reduce our energy threshold by about two orders of magnitude, still leaving such an occurrence very rare.
To assess such probabilities we consider what cataclysmic event could lead to the annihilation of not just human life, but also extremophiles, through the boiling of all water in Earth’s oceans. Surprisingly we find that although human life is somewhat fragile to nearby events, the resilience of Ecdysozoa such as Milnesium tardigradum renders global sterilisation an unlikely event. In this analysis we have considered only direct effects of astrophysical events such as the direct boiling of oceans; however such events could serve as a trigger for a second change. An example of this is the runaway greenhouse effect in which a less energetic event could evaporate a fraction of the ocean, which in turn leads to increased temperatures. Such an occurrence would have a lower threshold energy, as total evaporation of the oceans is no longer necessary; however the precise details of such an event are not known. As an upper bound, they presumed that this would have to increase global temperatures by a larger amount than seasonal variations and changes in solar output. In essence this would reduce our energy threshold by about two orders of magnitude, still leaving such an occurrence very rare.
Throughout this analysis they have made several assumptions, the primary being that life elsewhere will be similar to that found on Earth. To justify this assumption, they considered that when searches are conducted for exoplanetary life, the template used is that of life on Earth. They made the further assumption that life will evolve to adapt to the extreme environments of exoplanets as it has to those on Earth. Again, they justified this by the ubiquity of life across environmental conditions.
Finally, they noted that the type of life they expect to survive all but the most extreme of events is that which could survive elsewhere in our own solar system. The history of Mars indicates that it had an atmosphere that could have supported life, albeit in conditions that on Earth would be considered inhospitable, with both the Mars 2020 and ExoMars programs aiming for experimental verification. Organisms with similar tolerances to radiation and temperature such as tardigrades would be the only kind of
life that could survive long-terms in such conditions, and even then they would have to be significantly below the surface. The subsurface oceans that are posited to exist on Europa and Enceladus would have conditions similar to the deep oceans of Earth where taridgrades are found - volcanic vents providing heat in an environment devoid of light. The presence of extremophiles in the locations would be a significant step in narrowing the question of life starting on exoplanets.
Managed & Built by I2M Consulting, LLC | © 2010-
