Tidal Heating in Multilayered Terrestrial Exoplanets

Abstract

The internal pattern and overall magnitude of tidal heating for spin-synchronous terrestrial exoplanets from 1 to 2.5 R E is investigated using a propagator matrix method for a variety of layer structures. Particular attention is paid to ice-silicate hybrid super-Earths, where a significant ice mantle is modeled to rest atop an iron-silicate core, and may or may not contain a liquid water ocean. We find multilayer modeling often increases tidal dissipation relative to a homogeneous model, across multiple orbital periods, due to the ability to include smaller volume low viscosity regions, and the added flexure allowed by liquid layers. Gradations in parameters with depth are explored, such as allowed by the Preliminary Earth Reference Model. For ice-silicate hybrid worlds, dramatically greater dissipation is possible beyond the case of a silicate mantle only, allowing non-negligible tidal activity to extend to greater orbital periods than previously predicted. Surface patterns of tidal heating are found to potentially be useful for distinguishing internal structure. The influence of ice mantle depth and water ocean size and position are shown for a range of forcing frequencies. Rates of orbital circularization are found to be 10-100 times faster than standard predictions for Earth-analog planets when interiors are moderately warmer than the modern Earth, as well as for a diverse range of ice-silicate hybrid super-Earths. Circularization rates are shown to be significantly longer for planets with layers equivalent to an ocean-free modern Earth, as well as for planets with high fractions of either ice or silicate melting.

Venusian Habitable Climate Scenarios: Modeling Venus through time and applications to slowly rotating Venus-Like Exoplanets

“…These are the same numbers used for the modern Earth in R. Barnes (2017). Recent work by Henning and Hurford (2014) demonstrates that our choice for Q may not be unreasonable for Venus. Henning and Hurford (2014) give estimates of Q for Earthlike planets (see their Fig 15, top-center-row plot) with orbital periods from 0 to 200 days.…”

Full-lifetime simulations of multiple unequal-mass planets across all phases of stellar evolution

“…The particulars of this process are highly dependent on the composition of the approaching planet and the evolutionary stage of the star; all our bodies are point-masses with no assumed composition. The variation in tidal circularization behaviour and time-scale due to composition is so great (Henning & Hurford 2014) that any meaningful exploration would require a dedicated study, which we do not perform here. Our simulations here illustrate pre-conditions for this tidal interaction to occur.…”

Detectable close-in planets around white dwarfs through late unpacking

“…Consequently, a process such as tidal circularization of a terrestrial planet orbiting a WD must be taken on a case-by-case basis, one that is highly dependent on the rheology of the planet (but independent of the WD). The circularization timescale can easily vary by orders of magnitude depending on this rheology (Henning & Hurford 2014). Giant planets also suffer from this uncertainty, as they may contain solid cores, necessitating the combined modeling of fluid mechanics and solid mechanics.…”