Geophysical Surface Consequences for Terrestrial Exoplanets Subjected to Recent Orbital Scattering
Abstract
In early solar systems, the reorganization of planetary orbits often leads to ideal conditions for extreme geophysical surface phenomena, in particular for short-period terrestrial planets experiencing rapid changes in tidal forcing following close encounters with Jupiter-sized objects. Such orbital scattering events cause significant changes in orbital elements, which are effectively instantaneous on a geological timescale. In the few orbits immediately following such a scattering event, a planetary surface may remain in a colder more brittle state that has not yet adapted to increased extremes of cyclical tidal deformation, creating optimal conditions for severe surface fault production. In addition, changes in semi-major axis mean that terrestrial planets, if they had previously attained 1:1 spin-orbit synchronization, will be immediately desynchronized, often by a significant degree. We report the magnitude of possible surface fault production for a range of scattering parameters in terms of changes in eccentricity, inclination, and semi-major axis/orbital period. Full theoretical ranges are compared to specific close-encounter results obtained from N-body simulations including scattering between 1 Earth-mass and 1 Jupiter-mass planets around a 1 Solar-mass host. The role of interior structure is highlighted, with the thickness and rheology of a terrestrial world's crust found to be strong controls. Worlds with and without sub-lithospheric magma oceans are considered. Single-location accommodation of resultant strain for eccentricity-only outcomes can reach the order of opening 1-2 km wide faults in the orbits immediately following scattering. De-synchronization of spin can cumulatively enhance this to 4-8 km widths. Stresses often achieve failure thresholds, with tensile disruption depending primarily on the phenomenon of scale-weakening of crustal rocks. In addition to fault production, total crustal stain energy immediately increases following scattering, and the possibility of widespread earthquake activity is discussed. Additional consideration is made of higher-order terms in eccentricity and cross-terms in the tidal potential. Observability is limited by the rarity of such events, but perhaps enhanced by high IR brightness due to sudden extreme magmatic activity.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2018
- Bibcode:
- 2018AGUFM.P53C2984H
- Keywords:
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- 0328 Exosphere;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 0343 Planetary atmospheres;
- ATMOSPHERIC COMPOSITION AND STRUCTUREDE: 6207 Comparative planetology;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTSDE: 6296 Extra-solar planets;
- PLANETARY SCIENCES: SOLAR SYSTEM OBJECTS