Biotic Factors in Long-Term Planetary Habitability

The probability of long-term survival of putative life on exoplanets has direct implications for the prevalence of extant life elsewhere.  Environmental stability can be greatly attributed to abiotic features of a planetary body. However, we know that Earth’s current state is largely the result of life. Untangling biotic and abiotic influence, though, from Earth's deep history is difficult. To study these phenomena, we turn to computer simulation.  We utilize, modify, and, in some cases, combine Planets Model Code (Tyrrell 2020), Tangled Nature Model (Christensen et al. 2002), and Daisy World (Watson & Lovelock 1983) to conduct a series of computer experiments.  First, we modify and utilize Planets Model Code (Tyrrell 2020) to investigate worlds that harbor passive biota, which can only affect the environment in a random and unchanging manner over time. In this model, findings from a moderate sample study suggest that the probability of survival ( p_s ) of life grows considerably with the increase in life's viable temperature range ( ΔT ) and follows the power law: p_s ∝ ΔT ⁴. Also, we find that the chances of survival of any life on a given planet decrease linearly with time.  Finally, we discern that the chances of survival of eukaryotic analogues remain low regardless of their emergence time in a planet's history. We complement these findings with two additional studies. Our current endeavor is to create a new model that adds an active set of evolving and competing species which can affect temperature only on a local scale and temporary basis. To build this adaptive ecology simulation, we modify and merge Planets Model Code (Tyrrell 2020) and Tangled Nature Model (Christensen et al. 2002). Planets Model Code (Tyrrell 2020) is utilized to simulate the climactic characteristics of the exoplanet.  Tangled Nature Model (Christensen et al. 2002), which is utilized to run the ecological evolutionary model, operates in the form as modified by Arthur and Nicholson (2023), but with a few additional modifications of our own.  Findings from this effort are soon forthcoming.  Finally, we comment on plans for a future study, in which we propose a separate model wherein an active ecosystem is the dominant driving force in the stability, or lack thereof, of its home planet.  By assessing p_s in these limiting cases, we seek to understand if life can be a driver of planetary environmental stability.  

References: 

Arthur, Rudy and Arwen Nicholson (2023). “A Gaian Habitable Zone”. In: Monthly Notices of the Royal Astronomical Society 521.1. Publisher: Oxford University Press, pp. 690–707.

Christensen, Kim et al. (2002). “Tangled Nature: a Model of Evolutionary Ecology”. In: Journal of Theoretical Biology 216.1. Publisher: Elsevier, pp. 73–84.

Tyrrell, Toby (Oct. 2020). Planets Model code. DOI: 10.5281/zenodo.4081451.

Watson, Andrew J. and James E. Lovelock (Jan. 1983). “Biological Homeostasis of the Global Environment: the Parable of Daisyworld”. In: Tellus B: Chemical and Physical Meteorology 35.4, p. 284. ISSN: 1600-0889, 0280-6509.