Venus: A Thick Basal Magma Ocean May Exist Today

Abstract

Basal magma oceans develop in Earth and Venus after accretion as their mantles solidify from the middle outward. Fractional crystallization of the basal mantle is buffered by the core and radiogenic and latent heat in the magma ocean. Previous studies showed that Earth's basal magma ocean would have solidified after two or three billion years. Venus has a relatively hot interior that cools slowly in the absence of plate tectonics, which reduces heat flow through the solid mantle. Consequentially, the basal magma ocean could remain as thick as ~200–400 km today. Vigorous convection of liquid silicates could power a global magnetic field until recently while a core‐hosted dynamo is suppressed. The basal magma ocean may be a hidden reservoir of potassium and other incompatible elements. A high tidal Love number could reveal a basal magma ocean and would definitively establish that the core is at least partially liquid.

The Mantle Viscosity Structure of Venus

“…Nevertheless, we note that about 35% of the models present a viscosity decrease of over one order of magnitude from layer 3 to 4, which would correspond to a basal low viscosity zone. If confirmed, these regions could be analogous to the large low shear velocity provinces on Earth (e.g., French & Romanowicz, 2015) or indicate the presence of partial melting (O’Rourke, 2020). In contrast, the depth‐independent case (Figure 3c) requires an increase in viscosity in the mid mantle between the third and fourth layers at 1,330–1,550 km depth, which is significantly deeper than the ringwoodite‐bridgmanite phase transition.…”

Narrow range of early habitable Venus scenarios permitted by modeling of oxygen loss and radiogenic argon degassing

“…Additionally, 40 Ar may not be distributed homogeneously through Venus’s mantle. If Venus has mantle reservoirs enriched in incompatible elements or a thick basal magam occan ( 55 ), 40 Ar may be prevented from degassing to the atmosphere, increasing the number of our model runs compatible with Venus’s modern atmospheric 40 Ar concentration.…”

Ultrafast x-ray detection of low-spin iron in molten silicate under deep planetary interior conditions

“…The presence of highly conductive molten silicates at the base of the mantle may also have important implications for other rocky planets. For example, a recent model proposed that a basal magma ocean might have existed in Venus for a much longer period than Earth because of the higher internal temperatures expected for Venus ( 33 ). The model hypothesized that a dynamo could be generated solely from a Venusian basal magma ocean.…”