Evolutionary Exobiology II: investigating biological potential of synchronously-rotating worlds

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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.

Section: Resultsmentioning

confidence: 99%

“…Moreover, the manner in which oceans circulate may further limit (but possibly enhance) habitable regions by altering precipitation and temperature profiles (Cullum et al ., 2014; de Lavergne et al ., 2017; Stevenson, 2018a).…”

Section: Resultsmentioning

confidence: 99%

Niche amplitude, tidal-locking and Fermi's Paradox

Stevenson¹

2018

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“…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.…”

Section: Life On Tidally Locked Planetsmentioning

confidence: 99%

“…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.…”

Section: The Effect Of Tidal Locking and The Absence Of Seasonal And mentioning

confidence: 99%

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

Wandel

Gále

2019

The Kepler data show that habitable small planets orbiting Red Dwarf stars (RDs) are abundant, and hence might be promising targets to look at for biomarkers and life. Planets orbiting within the Habitable Zone of RDs are close enough to be tidally locked. Some recent works have cast doubt on the ability of planets orbiting RDs to support life.In contrast, it is shown that temperatures suitable for liquid water and even for organic molecules may exist on tidally locked planets of RDs for a wide range of atmospheres. We chart the surface temperature distribution as a function of the irradiation, greenhouse factor and heat circulation. The habitability boundaries and their dependence on the atmospheric properties are derived. Extending our previous analyses of tidally locked planets, we find that tidally locked as well as synchronous (not completely locked) planets of RDs and K-type stars may support life, for a wider range of orbital distance and atmospheric conditions than previously thought.In particular, it is argued that life clement environments may be possible on tidally locked and synchronously orbiting planets of RDs and K-type stars, with conditions supporting Oxygenic Photosynthesis, which on Earth was a key to Complex life. Different climate projections and the biological significance of tidal locking on putative complex life are reviewed. We show that when the effect of continuous radiation is taken into account, the Photo-synthetically Active Radiation (PAR) available on tidally locked planets, even of RDs, could produce a high Potential Plant Productivity, in analogy to mid-summer growth at high latitudes on Earth.Awaiting the findings of TESS and JWST, we discuss the implications of the above arguments to the detection of biomarkers such as liquid water and oxygen, as well as to the abundance of biotic planets and life.

“…Some are more restrictive than this (Merlis and Schneider, 2010). While these models apply specifically to aquaplanets, the climate models do offer a means of interrogating climate on telluric planets with land areas (Stevenson, 2018). If we consider realistic distributions of precipitation and consider the physiological impacts of this on water transport (Friend, 1993;Pockman and Sperry, 2000;Brienen et al, 2017), one should expect vegetation with lower heights in areas removed from the SSP on synchronous rotators.…”

Section: Effect On Climate Models For Synchronously Rotating Worldsmentioning

confidence: 99%

Planetary mass, vegetation height and climate

Stevenson¹

2019

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The maximum height trees can grow on Earth is around 122–130 m. The height is constrained by two factors: the availability of water, and where water is not limiting, the pressure available to drive the column of water along the xylem vessels against the pull of gravity (cohesion tension). In turn the height of trees impacts the biodiversity of the environment in a number of ways. On Earth the largest trees are found in maritime temperate environments along the Pacific Northwest coasts of northern California and southern Oregon. These forests provide a large number of secondary habitats for species and serve as moisture pumps that return significant volumes of water to the lower atmosphere. In this work, we apply simple mathematical rules to illustrate how super-terran planets will have significantly smaller trees, with concomitant effects on the habitability of the planet. We also consider the impact of varying tree height on climate models.