Habitable Zones & Global Climate

Blue Marble, Stagnant Lid: Could Dynamic Topography Avert A Waterworld?

By Keith Cowing
January 19, 2022
Filed under
Blue Marble, Stagnant Lid: Could Dynamic Topography Avert A Waterworld?
The four major endogenic sources of topography on a stagnant lid planet. (a) The component of dynamic topography due to flow-induced traction on the lithosphere. (b) Tectonic crustal thickening caused by tension over cold downwellings. (c) The component of dynamic topography due to thermal isostasy over thinned lithosphere. (d) Magmatic crustal thickening caused by melting of upwelling plumes.

Topography on a wet rocky exoplanet could raise land above its sea level. Although land elevation is the product of many complex processes, the large-scale topographic features on any geodynamically-active planet are the expression of the convecting mantle beneath the surface.

This so-called “dynamic topography” exists regardless of a planet’s tectonic regime or volcanism; its amplitude, with a few assumptions, can be estimated via numerical simulations of convection as a function of the mantle Rayleigh number.

We develop new scaling relationships for dynamic topography on stagnant lid planets using 2D convection models with temperature-dependent viscosity. These scalings are applied to 1D thermal history models to explore how dynamic topography varies with exoplanetary observables over a wide parameter space. Dynamic topography amplitudes are converted to an ocean basin capacity, the minimum water volume required to flood the entire surface. Basin capacity increases less steeply with planet mass than does the amount of water itself, assuming a water inventory that is a constant planetary mass fraction.

We find that dynamically-supported topography alone could be sufficient to maintain subaerial land on Earth-size stagnant lid planets with surface water inventories of up to approximately 10βˆ’4 times their mass, in the most favourable thermal states. By considering only dynamic topography, which has ~1-km amplitudes on Earth, these results represent a lower limit to the true ocean basin capacity. Our work indicates that deterministic geophysical modelling could inform the variability of land propensity on low-mass planets.

Claire Marie Guimond, John Rudge, Oliver Shorttle

Comments: 33 pages, 9 figures, submitted to The Planetary Science Journal
Subjects: Earth and Planetary Astrophysics (astro-ph.EP)
Cite as: arXiv:2201.05636 [astro-ph.EP] (or arXiv:2201.05636v1 [astro-ph.EP] for this version)
Submission history
From: Claire Guimond
[v1] Fri, 14 Jan 2022 19:25:24 UTC (2,393 KB)

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) πŸ––πŸ»