The potential of planets orbiting red dwarf stars to support oxygenic photosynthesis and complex life

Abstract

We review and reassess the latest findings on the existence of extra-solar system planets and their potential of having environmental conditions that could support Earth-like life. Within the last two decades, the multi-millennial question of the existence of extra-Solarsystem planets has been resolved with the discovery of numerous planets orbiting nearby stars, many of which are Earth-sized (and some even with moderate surface temperatures).Of particular interest in our search for clement conditions for extra-solar system life are planets orbiting Red Dwarf (RD) stars, the most numerous stellar type in the Milky Way galaxy. We show that including RDs as potential life supporting host stars could increase the probability of finding biotic planets by a factor of up to a thousand, and reduce the estimate of the distance to our nearest biotic neighbor by up to 10. We argue that multiple star systems need to be taken into account when discussing habitability and the abundance of biotic exoplanets, in particular binaries of which one or both members are RDs. Early considerations indicated that conditions on RD planets would be inimical to life, as their Habitable Zones (where liquid water could exist) would be so close as to make planets tidally locked to their star. This was thought to cause an erratic climate and expose life forms to flares of ionizing electro-magnetic radiation and charged particles. Moreover, it has been argued that the lesser photon energy of the radiation of the relatively cool RDs would not suffice for Oxygenic Photosynthesis (OP) and other related energy expending reactions. Recent calculations show that these negative factors are less severe than originally thought. Numerous authors suggest that OP on RD planets may evolve to utilize photons in the infrared. We however argue, by analogy to the evolution of OP and the environmental

Colloquium: Physical constraints for the evolution of life on exoplanets

“…It was argued by Gale and Wandel (2017) that oxygenic photosynthesis in the PAR is feasible on planets around low-mass stars, primarily because the side facing the star (assuming synchronous rotation) will receive continuous illumination that compensates for the moderate photon flux. A detailed analysis of the prospects for photosynthesis on Proxima b was undertaken by Ritchie et al…”

How far are extraterrestrial life and intelligence after Kepler?

“…However, 16 years later, several of the assumptions in this work were found or shown to be inaccurate: terrestrial planets in the habitable zone, even of G-stars, were found to be frequent, M stars were shown to be less hostile to host planets with conditions life than previously thought (e.g. Tarter et al 2007;Seager and Demming 2010;Gale and Wandel 2016), and planets in the Habitable Zone of RDs were argued to be able to support liquid water and photosynthesis for a wide range of atmospheric and other properties (Wandel 2016). If RD planets are suitable for life this would imply that about half of the stars in the Galaxy could harbor a biotic planet and correspondingly enhance the potential abundance of civilizations.…”

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

“…Maximum GPP at 55 o N was found to be very high (in midsummer) resulting in an annual GPP (almost entirely produced in the summer months) reaching to about one third of that in the tropics (0±10 o latitude). By extrapolation, this should at least double the productivity on TLPs as calculated by Ritchie et al Furthermore, damaging levels of radiation would be avoided on TLPs, by the plants "selecting" locations with optimum radiation regimes, between the Sub-stellar point and light termination (Gale and Wandel 2017).…”