Abstract
It has been established theoretically that atmospheric thermal tides on rocky planets can lead to significant modifications of rotational evolution, both close to synchronous rotation and at faster rotations if certain resonant conditions are met. Here it is demonstrated that the normally considered dissipative gravitational tidal evolution of rocky planet rotation could, in principle, be “stalled” by thermal tide resonances for Earth-analog worlds in the liquid–water orbital zone of stars more massive than nsim 0.3{M_ odot }n. The possibility of feedback effects between a planetary biosphere and the planetary rotational evolution is examined. Building on earlier studies, it is suggested that atmospheric oxygenation and ozone production could play a key role in planetary rotational evolution, and therefore represents a surprising but potent form of biological imprint on astronomically accessible planetary characteristics.
Highlights
Differential, inelastic deformations of planets arise due to the gravitational effect of a perturbing body
It is suggested that atmospheric oxygenation and ozone production could play a key role in planetary rotational evolution, and represents a surprising but potent form of biological imprint on astronomically accessible planetary characteristics
Planetary atmospheres are subject to thermal tides due to stellar radiation, and these tides can alter atmospheric mass distributions leading to additional torques that are transferred to the solid body motion
Summary
Differential, inelastic deformations of planets arise due to the gravitational effect of a perturbing body. The resulting thermal tide torques would have been comparable with the dominant lunar tidal torque at that time (Fig. 1), leading to a ‘‘stalling’’ of Earth’s rotational slowdown while the lunar orbit continued to evolve The details of this resonant trapping hinge on numerous factors, including the resonance width (and the timescale over which restoring forces must act: a few 10– 1p00ffiffiffiffiffimffiffiffiffiillion years), atmospheric composition (through the m=T scaling and the efficiency of radiation absorption), surface temperature, and specifics of dissipative processes in atmospheric waves. Higher temperature lowers the daylength for resonance (i.e., moving curve in Figure 1 to the right,pbyffiffiffiaffiffiffilffitffieffi ring atmospheric column height according to the m=T dependency), allowing the planet to escape back to its longterm spin-down driven by lunar and solar tidal torques Other mechanisms, such as changes in oceanic dissipation, could be at play. It is assumed here that many Earth-analog worlds have initial rotation rates fast enough that thermal tides will eventually encounter the resonant state as solar tides slow the rotation
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