Venus

Venus is a rocky planet in the solar system, very similar to Earth in its size and composition. However, it has a much higher surface temperature than our own planet. This higher surface temperature could also affect the surface manifestation of the internal dynamics. The atmosphere on Venus is much denser than on Earth and is made up mostly (96%) of carbon dioxide and the rest nitrogen.

Venus’s radius is 6 051 km and its mass is about 82% of Earth’s mass. The mean (average) density of Venus is about 5.2 g/cm3. Through Project Magellan, the surface of Venus was mapped and found to show evidence of volcanism. Sulphur in the atmosphere shows evidence for recent volcanism. It also lacks many impact craters implying the surface is relatively young, about 300-600 million years old.

Structure of Venus

Like the Earth, and other rocky planets, Venus differentiated after for- mation and has a similar structure, with a core, mantle and a crust. Because we do not have seismic data from Venus, we have little information about it’s internal structure beyond this basic division. Venus’s size and density is fairly close to that of Earth. Since Venus formed at the same time as Earth it has been cooling at about the same rate, which means a partially liquid core is likely (as observed on Earth).

The core of Venus has a radius of about 3000 km. The core is mostly ( 80%) iron, 6% nickel and some sulphur and little to no oxygen. The main difference between Venus and Earth is that Venus lacks evidence of plate tectonics at the surface.

Dynamics of Venus

While on Earth, the crust undergoes continuous subduction and recycling at the plate boundaries, the crust on Venus appears to be locked, like on Mars. However, unlike Mars there is no evidence for recent tectonic activity. Given it’s young surface age, it’s inferred that the entire planet experienced a global resurfacing event. The mantle temperatures rise, weakening the crust and then a large subduction event starts until the entire surface is recycled. It is thought this process occurs cyclically on Venus. We refer to this as surface in an episodic regime, as there are episodes of resurfacing subduction followed by long episodes of stagnant lid convection (where the surface is rigid and locked).

Video of stagnant lid convection

Here we see a video of mantle convection as it might appear today on Mars. Because there is no longer any tectonic activity on the surface, the planet is currently in a stagnant lid regime, where the mantle convects, but the surface does not subduct into the mantle. The surface is not being replenished with new material, instead it grows thicker over time, as the mantle cools at the surface.

Video of a Mobile lid convection

Here we see subduction starting, and soon most of the surface has been recycled into the mantle. After this event, it is likely the surface locks up again, and slowly the crust will grow thicker over time until it becomes unstable, triggering another resurfacing event.