Role of stellar physics in regulating the critical steps for life

Abstract

We use the critical step model to study the major transitions in evolution on Earth. We find that a total of five steps represents the most plausible estimate, in agreement with previous studies, and use the fossil record to identify the potential candidates. We apply the model to Earth-analogs around stars of different masses by incorporating the constraints on habitability set by stellar physics including the habitable zone lifetime, availability of ultraviolet radiation for prebiotic chemistry, and atmospheric escape. The critical step model suggests that the habitability of Earth-analogs around M-dwarfs is significantly suppressed. The total number of stars with planets containing detectable biosignatures of microbial life is expected to be highest for Kdwarfs. In contrast, we find that the corresponding value for intelligent life (technosignatures) should be highest for solar-mass stars. Thus, our work may assist in the identification of suitable targets in the search for biosignatures and technosignatures.

Colloquium: Physical constraints for the evolution of life on exoplanets

“…In the event that t p is much less than t HZ , i.e. the temporal duration of the HZ, it is the former that will serve as an upper limit on the time over which biological evolution can occur; the expression for t HZ as a function of M is found in Rushby et al (2013) and Lingam and Loeb (2019a). This is because of the fact that the presence of an atmosphere is necessary for sustaining liquid water on the surface as seen from its phase diagram.…”

“…where κ ≈ 3 for M M , κ ≈ 1 for M M and t A,⊕ is the timescale for the origin of life on Earth, which has a strict upper bound of 0.8 Gyr. Coupled to the fact that Earth-analogs around M-dwarfs are expected to lose their atmospheres more rapidly, it was proposed that stars with M 0.4M are relatively unlikely to host biospheres (Lingam and Loeb, 2019a).…”

Multiverse Predictions for Habitability: Fraction of Planets that Develop Life

“…A biological perspective was applied to try to identify what these steps could be in Reference [51] on the basis of reorganizations of information processing, and is consistent with this number, and including the distribution of these other purported hard steps in time bolsters the agreement with this model. The hard step model was combined with stellar activity models to deduce that life should be most probable around K dwarfs in Reference [52]. One important consequence of this model is that intelligent life should be quite rare in the universe, since it relies on a sequence of improbable events.…”

Photosynthesis on habitable planets around low-mass stars

“…In other words, it is conceivable that planets host life but are not detectable by seeking signatures of O2 and O3 because of the simple fact that the concentrations of these gases in the atmosphere would be too low. 1 The Earth, for instance, possessed a largely anoxic atmosphere until ∼ 2.4 Ga with near-modern O2 levels having been achieved only 0.5 Ga (Lyons et al 2014;Knoll & Nowak 2017;Catling & Kasting 2017;Lingam & Loeb 2018a). Hence, Figure 2 can assist in the identification of suitable target planets based on the stars that they orbit (Lingam & Loeb 2018c).…”