  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 $10^{-4}$ 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.
