Planetary targets in the search for extrasolar oxygenic photosynthesis

Abstract

Background:In the coming decades space telescopes will be constructed that will attempt to find the gaseous products of oxygenic photosynthesis, the most promising biosignatures of life, in the atmospheres of temperate Earth-like planets orbiting distant stars. Aims: This paper aims to provide a synthesis of the range of feasible targets -either planets or their satellites -that could harbour photosynthesis. Methods: We calculated photosynthetically active radiation (PAR) fluxes on a diversity of planetary bodies including those receiving direct light from a single star, similarly to the Earth, and investigated the potential of these fluxes to support photosynthesis. Results: All main sequence stars emit radiation that is capable of supporting photosynthesis on Earth-like planets. We discuss tidally-locked M star planets as a special case. Less conventional targets for searches include large moons orbiting gas giant planets, which receive reflected light from their host planets and from the host star, planets in stable orbits in binary star systems, and the search for two planets within the same star system with photosynthetic signatures. Conclusions: A diversity of planetary bodies are targets in the search for extrasolar photosynthesis. The demonstration that many or none of these candidate planetary bodies harbour photosynthesis would be an important conclusion in understanding the evolution and prevalence of photosynthesis.

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

“…This was a period from ~ 550 to 470 million years ago when life advanced from 3.3 billion years of mainly single celled organisms to multi-cellular, complex life forms (Fig.1). For all these reasons, OP and conditions for OP are primary targets in the search for advanced extrasolar life (Cockell et al, 2009). Although there were (and still are), a number of problems for the biota resulting from the oxygen-rich atmosphere produced by OP, without its appearance on Earth there would probably have been no complex life as we know it.…”

Spectro-Thermometry of M Dwarfs and Their Candidate Planets: Too Hot, Too Cool, or Just Right?

“…5 We find that these candidate HZ planets receive anywhere from 10% to 45% of the PAR as the Earth ( Figure 16); this varies somewhat from the of Wolstencroft & Raven (2002) in part because these stars cover a range of spectral types. However, lest this dim prospects for plants on M dwarf planets, the reduced PAR is still orders of magnitude higher than the minimum light requirement of terrestrial oxygen-evolving photosynthetic life (Cockell et al 2009). Indeed, operation of the photosystem II moiety of oxygenic photosynthesis can be inhibited by high light conditions (photoinhibition; Long et al 1994), a phenomenon which would be relieved in the HZ of an M dwarf.…”

Photosynthetic potential of planets in 3 : 2 spin–orbit resonances

“…If photosynthetic organisms live in a marine environment, or within substrates such as rock, then they can satisfactorily avoid strong UV flares (Cockell et al, 1999;Cockell et al, 2009). Planets with thick cloud cover may offer extra UV protection (Mayer et al, 1998).…”

“…Life operating with oxygenic photosynthetic machinery, whereby the host star's energy is the primary energy source and oxygen is the waste product, is a promising biosignature, as well as having the greatest potential for driving primary productivity (Wolstencroft & Raven, 2002 ;Raven & Cockell, 2006), and consequently there has been significant interest into the potential for planets to host photosynthetic life in single star systems (Wolstencroft & Raven, 2002;Cockell et al, 2009). …”