Instead recent 3D calculations of the inner edge are beginning to employ fully

Instead recent 3d calculations of the inner edge are

This preview shows page 29 - 31 out of 48 pages.

Instead, recent 3D calculations of the inner edge are beginning to employ fully-coupled atmospheric ocean models (e.g., [ 30 , 244 ]). Better cloud and convection schemes have also continued to improve such calculations (e.g., [ 240 ]). Thus, the real future of habitability studies will be improved 1D and 3D models. However, better observations are truly needed to usher in a computer modeling renaissance, leading to an enhanced theoretical understanding that will advance 1D and 3D exoplanet habitability models alike [ 134 ]. Without better observations that can guide model predictions, all the increased model complexity, flexibility, or computational speed will be for naught.
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Geosciences 2018 , 8 , 280 30 of 48 14. An Appraisal of Superhabitability Although the search for life has partially focused on finding a “second Earth”, Heller and Armstrong [ 265 ] argue that other worlds can offer conditions that are even more suitable for life to emerge and evolve than those that have existed on our planet. These authors offer many examples of planetary traits that might characterize such “superhabitable worlds”, which generally suggests that planets that are somewhat bigger, more massive, more water-rich, or dryer than the Earth (to name a few) are likely to be even more habitable than our planet. However, a growing body of work demonstrates that predicting superhabitability may be challenging and different outcomes are possible depending on the relative influences of various factors. I will highlight a few of the traits that Heller and Armstrong [ 265 ] have considered for superhabitability, while giving an alternate point of view. It was suggested that planets slightly more massive than Earth may be superhabitable because plate tectonics should last longer [ 265 ]. However, simulations indicate that basal shear stresses that are too high can induce plate failure on planets that are only slightly more massive than the Earth [ 64 ]. Although a larger water surface area (smaller continental area) was also associated with superhabitability [ 265 ], such a planet should exhibit slower continental weathering rates, allowing atmospheric CO 2 concentrations to rise, assuming an operative carbon-cycling mechanism [ 266 ]. This may or may not make the planet too hot for life, depending on other planetary characteristics. Dry planets with shallower waters and more fractionate continents, than the Earth may have enriched habitat diversity [ 265 ]. However, with less continental area, there should also be less plants (if otherwise an Earth-clone), and less photosynthesis and atmospheric oxygen. At low enough oxygen levels, not only would potential biosignatures be difficult to detect (e.g., [ 106 ]), but fire may not be possible [ 127 ] . Plus, the smaller volume to surface area ratio of shallower fragmented water bodies may facilitate their freezing.
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