Could photosynthesis function on Proxima Centauri b?

Abstract

Could oxygenic and/or anoxygenic photosynthesis exist on planet Proxima Centauri b? Proxima Centauri (spectral type – M5.5 V, 3050 K) is a red dwarf, whereas the Sun is type G2 V (5780 K). The light regimes on Earth and Proxima Centauri b are compared with estimates of the planet's suitability for Chlorophyll a (Chl a) and Chl d-based oxygenic photosynthesis and for bacteriochlorophyll (BChl)-based anoxygenic photosynthesis. Proxima Centauri b has low irradiance in the oxygenic photosynthesis range (400–749 nm: 64–132 µmol quanta m−2 s−1). Much larger amounts of light would be available for BChl-based anoxygenic photosynthesis (350–1100 nm: 724–1538 µmol quanta m−2 s−1). We estimated primary production under these light regimes. We used the oxygenic algae Synechocystis PCC6803, Prochlorothrix hollandica, Acaryochloris marina, Chlorella vulgaris, Rhodomonas sp. and Phaeodactylum tricornutum and the anoxygenic photosynthetic bacteria Rhodopseudomonas palustris (BChl a), Afifella marina (BChl a), Thermochromatium tepidum (BChl a), Chlorobaculum tepidum (BChl a + c) and Blastochloris viridis (BChl b) as representative photosynthetic organisms. Proxima Centauri b has only ≈3% of the PAR (400–700 nm) of Earth irradiance, but we found that potential gross photosynthesis (Pg) on Proxima Centauri b could be surprisingly high (oxygenic photosynthesis: earth ≈0.8 gC m−2 h−1; Proxima Centauri b ≈0.14 gC m−2 h−1). The proportion of PAR irradiance useable by oxygenic photosynthetic organisms (the sum of Blue + Red irradiance) is similar for the Earth and Proxima Centauri b. The oxygenic photic zone would be only ≈10 m deep in water compared with ≈200 m on Earth. The Pg of an anoxic Earth (gC m−2 h−1) is ≈0.34–0.59 (land) and could be as high as ≈0.29–0.44 on Proxima Centauri b. 1 m of water does not affect oxygenic or anoxygenic photosynthesis on Earth, but on Proxima Centauri b oxygenic Pg is reduced by ≈50%. Effective elimination of near IR limits Pg by photosynthetic bacteria (<10% of the surface value). The spectrum of Proxima Centauri b is unfavourable for anoxygenic aquatic photosynthesis. Nevertheless, a substantial aerobic or anaerobic ecology is possible on Proxima Centauri b. Protocols to recognize the biogenic signature of anoxygenic photosynthesis are needed.

Constraints on Aquatic Photosynthesis for Terrestrial Planets around Other Stars

“…m for a late-type M-dwarf analogous to TRAPPIST-1 (T = 2500 K). These numbers are in reasonable agreement with the corresponding values of 185 m and 10 m calculated for Earth and Proxima b, respectively(Ritchie et al 2018, …”

“…Thus, communities circulating in this layer are theoretically 3 This result seems compatible with the detection of microalgae at depths of 285 m on Earth (Valiela 2015, Chapter 3.1). 4 As per empirical data and theoretical constraints, F C ∼ 0.01 µmol m −2 s −1 is compatible with anoxygenic photoautotrophs (Raven et al 2000;Manske et al 2005), but the prior conservative limit is adopted for comparison against Ritchie et al (2018). capable of survival and growth.…”

Extremophile Microalgae: the potential for biotechnological application

“…Ritchie et al. () discussed the possibility of a photosynthetic ecology existing on Proxima Centauri b which appears to be a viable habitable planet. Several researches addressed the evaluation of the survival capacity of extremophile/extremotolerant organisms when facing harsh conditions, including those of outer space or of simulated Martian environment (Duarte et al.…”

The bio-habitable zone and atmospheric properties for planets of red dwarfs

“…Although they radiate less photons in the Photo-synthetically Active Radiation (PAR) waveband (400-700nm) than is incident on Earth, there is still enough PAR flux to support Earth-like plant life (Gale and Wandel,2017). Ritchie et al (2018) made theoretical estimates and laboratory measurements of the photosynthesis of different species of algae exposed to radiation levels which could be expected at the Sub-stellar points of TLPs. They concluded that the PAR incident on TLPs may produce high levels of basic plant productivity: from 13-22% of what would be expected on Earth.…”