Niche amplitude, tidal-locking and Fermi's Paradox

Abstract

Abstract‘Where is everybody?’ remarked Enrico Fermi, leading to the famous, and as yet unanswered ‘Fermi's Paradox’ as this remark has come to be known. While there are a number of possible solutions that vary from the distances are too great; the cost prohibitive or civilizations naturally decline or eliminate themselves before interstellar travel becomes possible, none of these are intellectually satisfying. More recently, Manasvi Lingam and Abraham Loeb suggested that for those planets orbiting red dwarfs, atmospheric erosion may be a partial solution to this ‘paradox’. Such planets may experience greater exposure to stellar winds and/or extreme ultraviolet and X-radiation (henceforth abbreviated to EUV). While this proposition is undeniably reasonable, it is likely incomplete. A more fundamental limitation on the development of biological complexity is imposed by plate tectonics: time. On asynchronously rotating planets, the habitable area for any species is defined by latitudinal bands that encompass the globe. Conversely, on synchronous rotators, the comparative habitable area is limited to broadly concentric regions surrounding the Sub-Stellar Point (SSP). Given that terrestrial mammals and from them humans evolved in tropical or subtropical regions, the geographical area subtended with these conditions is likely to be smaller and transected by suitable landmasses for shorter periods than on asynchronously rotating worlds. Habitable subaerial regions for individual species are therefore more limited in area. This leads to a greater limitation on the temporal intervals over which biological complexity can evolve.

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

“…Recently Stevenson and Large (2017), Stevenson (2018 a , 2018 b ) considered that the surface temperature structure of locked planets would deny the development of biological complexity, as the habitable belt around the sub-stellar point may be narrower than the latitudinal habitable bands on asynchronously rotating planets. However, as can be seen in Fig.…”

“…These temporal responses are governed by mechanisms which measure day/night length and temperature cycles (Lambers et al ., 2008). Such adaptations would be absent on TLPs, where plants would be exposed to continuous steady radiation, although geographic features (Stevenson, 2018 a , 2018 b ) and planet obliquity (Kite et al ., 2011) may produce some climate variations.…”

Phytoclimatic mapping of exoplanets

“…Therefore, one should always expect that the area of land that is habitable for complex life will be less on synchronously-rotating worlds than those that have asynchronous rotation. This gives a quantitative assessment of the habitability in relation to addressing the Fermi Paradox (Stevenson, 2018b). With less habitable surface on which complex life can evolve and fill niches, the evolutionary complexity of life on these worlds will always be lower than that it is on asynchronously-rotating planets.…”

“…This assumption is based solely on the biological requirements for the development and succession of life on Earth. The data can be combined or compared with other analyses based on niche volume and produce regionally accurate models of habitability (Gatti, 2016; Stevenson, 2018 a , 2018 b ).…”