Geodynamics and Rate of Volcanism on Massive Earth-Like Planets

Abstract

We provide estimates of volcanism versus time for planets with Earth-like composition and masses 0.25 -25 M ⊕ , as a step toward predicting atmospheric mass on extrasolar rocky planets. Volcanism requires melting of the silicate mantle. We use a thermal evolution model, calibrated against Earth, in combination with standard melting models, to explore the dependence of convection-driven decompression mantle melting on planet mass. We show that (1) volcanism is likely to proceed on massive planets with plate tectonics over the main-sequence lifetime of the parent star; (2) crustal thickness (and melting rate normalized to planet mass) is weakly dependent on planet mass; (3) stagnant lid planets live fast (they have higher rates of melting than their plate tectonic counterparts early in their thermal evolution), but die young (melting shuts down after a few Gyr); (4) plate tectonics may not operate on high mass planets because of the production of buoyant crust which is difficult to subduct; and (5) melting is necessary but insufficient for efficient volcanic degassing -volatiles partition into the earliest, deepest melts, which may be denser than the residue and sink to the base of the mantle on young, massive planets. Magma must also crystallize at or near the surface, and the pressure of overlying volatiles must be fairly low, if volatiles are to reach the surface. If volcanism is detected in the τ Ceti system, and tidal forcing can be shown to be weak, this would be evidence for plate tectonics.

The habitability of a stagnant-lid Earth

“…Batalha 2014), it has proven difficult to establish only on the basis of mass and radius whether plate tectonics is more or less likely to occur than on Earth. While some authors argue for a reduced tendency for plate tectonics to take place on these bodies (O'Neill & Lenardic 2007;Kite et al 2009;Stamenković et al 2012;Stein et al 2013), others favour an increased tendency (Valencia et al 2007;van Heck & Tackley 2011;O'Rourke & Korenaga 2012) or suggest that the tectonic behaviour of a rocky body can be strongly affected by the specific thermal conditions present after planetary formation and by the particular thermochemical history experienced by the interior (e.g. Noack & Breuer 2014;O'Neill et al 2016).…”

WATER LOSS FROM TERRESTRIAL PLANETS WITH CO2-RICH ATMOSPHERES

“…Because of the diversity of planetary formation histories, it is likely that many terrestrial exoplanets will form with much more H 2 O than Earth possesses. Depending on the efficiency of processes that partition water between the surface and mantle, many such planets would then be expected to have deep oceans, with little or no rock exposed to the atmosphere (Kite et al 2009;Elkins-Tanton 2011). Given an Earth/Venus-like total CO 2 inventory, these waterworlds 3 could be expected to have much higher atmospheric CO 2 than Earth today due to inhibition of the land carbonate-silicate cycle.…”

“…We then use an iterative procedure to calculate equilibrium temperature and water vapor profiles self-consistently. We show that in certain circumstances, strong temperature inversions may occur in the low atmosphere due to absorption of incoming 3 Here we use the term "waterworld" for a body with enough surface liquid water to prevent subaerial land, but not so much H 2 O as to inhibit volatile outgassing (see, e.g., Kite et al 2009, Elkins-Tanton 2011, following Abbot et al (2012). We use the term "ocean planet" for any planet covered globally by liquid H 2 O, without any constraint on the total water volume (Léger et al 2004;Fu et al 2010).…”

Melting in super-earths

“…The interior temperature controls long-term planetary evolution and processes with potentially observable consequences such as volcanism and magnetic field generation. The volcanic flux and magnetic field strength both scale with the heat flux out of the interior F [12,13]. Assuming the flux is dominated by thermal convection and neglecting internal heat sources such as those owing to radioactive decay or tidal heating where T TBL is the temperature contrast across the thermal boundary layer, and the properties within the boundary layer: ρ is density, α is the volumetric thermal expansivity, g is gravitational acceleration, C P is isobaric heat capacity, k is thermal conductivity and η is dynamic viscosity [14].…”