Dynamical considerations for life in multihabitable planetary systems

TL;DR

This study investigates how planet-planet interactions in multihabitable systems influence climate stability and the potential for life transfer, finding that close proximity favors habitability without significant obliquity variations or impact on lithopanspermia.

Contribution

It provides new insights into the effects of resonant interactions on climate stability and lithopanspermia in multihabitable planetary systems.

Findings

Resonant interactions do not cause larger obliquity variations.

Resonant interactions are not a primary factor in lithopanspermia.

Close proximity enhances lithopanspermia rates significantly.

Abstract

Inspired by the close-proximity pair of planets in the Kepler-36 system, we consider two effects that may have important ramifications for the development of life in similar systems where a pair of planets may reside entirely in the habitable zone of the hosting star. Specifically, we run numerical simulations to determine whether strong, resonant (or non-resonant) planet-planet interactions can cause large variations in planet obliquity---thereby inducing large variations in climate. We also determine whether or not resonant interactions affect the rate of lithopanspermia between the planet pair---which could facilitate the growth and maintenance of life on both planets. We find that first-order resonances do not cause larger obliquity variations compared with non-resonant cases. We also find that resonant interactions are not a primary consideration in lithopanspermia. Lithopanspermia is enhanced significantly as the planet orbits come closer together---reaching nearly the same rate as ejected material falling back to the surface of the originating planet (assuming that the ejected material makes it out to the location of our initial conditions). Thus, in both cases our results indicate that close-proximity planet pairs in multihabitable systems are conducive to life in the system.