Habitability and atmospheric pressure

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Habitability and atmospheric pressure

Post by Lazarus on 21st February 2013, 1:13 pm

Wasn't sure whether to add this to the new habitable zone estimates discussion or not...

The habitable zone of Earth-like planets with different levels of atmospheric pressure
http://arxiv.org/abs/1302.4566

Considers planets with atmospheric pressure from 0.1 3 bar, and various other effects such as eccentricity, obliquity, rotation period.

The estimate of the habitable zone for Earth-like atmospheres is quite narrow:
Our inner edge, calculated for Earth-like pressure, cloudiness and humidity, is located at a = 0.82 AU, in the range of the inner limits predicted by Selsis et al. (2007). Our outer edge, calculated for Earth-like atmospheric composition, lies at a = 1.08 AU, much closer to the star than the quoted outer limits of the classic HZ, which are estimated for CO2-rich planetary atmospheres (Kasting et al. 1993, Selsis et al. 2007).
Also to note:
Our calculations do not include the CO2 climate stabilization mechanism considered in the classic HZ definition (Kasting et al., 1993). In principle, EBM models can be used to simulate the carbonate-silicate cycle that drives this mechanism (WK97). However, this choice is not practical when running thousands of simulations, as we do here, because the time-scale of the CO2 cycle is much larger than the time-scale of convergence of the simulations. In addition, modeling the carbonate-silicate cycle requires ad hoc assumptions on the silicate weathering law and rate of CO2 production by volcanos. At the present time it is not clear if an active volcanism and tectonics, the ingredients required for the existence of the CO2 cycle, are common in terrestrial planets. For planets that do have this cycle, the outer edge of the HZ would shift to larger values of semi-major axis than estimated here. For completeness we note that, if oceans are salty, the outer edge would shift in the same direction due to the lowering of the water freezing point.
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