Does the Evolution of Complex Life Depend on the Stellar Spectral Energy Distribution?

Abstract

This paper presents the proportional evolutionary time hypothesis, which posits that the mean time required for the evolution of complex life is a function of stellar mass. The "biological available window" is defined as the region of a stellar spectrum between 200 to 1200 nm that generates free energy for life. Over the ∼4 Gyr history of Earth, the total energy incident at the top of the atmosphere and within the biological available window is ∼ 10 34 J. The hypothesis assumes that the rate of evolution from the origin of life to complex life is proportional to this total energy, which would suggest that planets orbiting other stars should not show signs of complex life if the total energy incident on the planet is below this energy threshold. The proportional evolutionary time hypothesis predicts that late K-and M-dwarf stars (M < 0.7 M⊙) are too young to host any complex life at the present age of the universe. F-, G-, and early K-dwarf stars (M > 0.7 M⊙) represent the best targets for the next generation of space telescopes to search for spectroscopic biosignatures indicative of complex life. 1.

The Resilience of Habitable Climates Around Circumbinary Stars

“…The period of instellation experienced by circumbinary planets poses a more complex pattern than a single‐star system: The inference of natural numbers from the setting stars might be more difficult in such a system, although perhaps such added complexity would enhance the evolution of technology. The “proportional evolutionary time” hypothesis (Haqq‐Misra, 2019) suggests that the evolutionary timescale for complex life depends upon the availability of free energy between 200 and 1,000 nm. The incident radiation for an Earth‐like circumbinary planet with different spectral host stars (e.g., a G‐dwarf primary and K‐dwarf secondary) will show a similar time‐mean irradiance within this wavelength range compared to a planet orbiting a single‐star at an equivalent orbital distance.…”

Um critério energético para o desenvolvimento de vida em um exoplaneta

“…No início desta seção seguiremos os desenvolvimentos apresentados por Haqq-Misra na Ref. [5]. É importante já ressaltar que esta análise poderá ser estendida a qualquer outro sistema planetário.…”

“…Neste artigo faremos uma revisão da hipótese do tempo evolutivo proporcional cuja abreviação em inglês é PET. 2 Proposta nas referências [4,5], a hipótese PET relaciona o tipo espectral da estrela hospedeira a com a probabilidade da existência de vida complexa. Segundo os resultados apresentados nestas referências, o tempo necessário para o desenvolvimento da vida complexa em planetas que orbitam estrelas com massas menores que a do Sol, como estrelas tipo K e M, deve ser bem maior que a idade do universo.…”

Testing Earth-like atmospheric evolution on exo-Earths through oxygen absorption: required sample sizes and the advantage of age-based target selection

“…Since the advent of oxygenic photosynthesis is presumed a prerequisite for global oxygenation, the rate at which evolutionary changes occur in the biosphere could also limit the oxygenation timescale. Several authors have investigated factors affecting the pace of biological evolution on planets hosted by low-mass stars, with some suggesting that prebiotic chemistry could be inhibited by a deficit of ultraviolet radiation (Buccino et al 2007;Ranjan et al 2017;Rimmer et al 2018), and others proposing that complex life could take longer to subsequently evolve (Haqq-Misra & Kopparapu 2018;Haqq-Misra 2019). Biogenic oxygen levels may be substantially lower around low-mass stars, as they emit less of the visible-wavelength radiation which drives oxygenic photosynthesis on Earth (e.g., Kiang et al 2007;Gale & Wandel 2016;Lehmer et al 2018;Mullan & Bais 2018;Ritchie et al 2018;Lingam & Loeb 2018.…”