Corona

So far, coronae have been found only on Venus. Some of the conditions for corona formation also exist on Earth, but the landforms that result there never become coronae.

Coronae are round volcano-tectonic structures. Their main features are a circular rise with a trough directly beside it, at the rim. Together these give the basic corona shape. The interior may be a raised dome, a plateau or a basin, and it may have a peak. It may also hold many other volcanic or tectonic forms: fractures, domes and shields.

They are 60–1100 km across. The exception is the largest, Artemis Corona, which is 2600 km across. It sits at the centre of a mantle flow that affects the whole of Venus (Hansen 2018). For this reason it may be regarded as a landform type of its own, a superstructure.

The shape of a corona tells us whether it is active now or “extinct” (Gülcher et al. 2020). If there is an active mantle upwelling beneath it, its centre is a raised dome. If the upwelling has stopped, the interior slowly “settles”, and in time it becomes a basin. A rampart then forms around its edge.

The most popular theory of corona formation is the hot-spot model. Here a hot mantle upwelling pushes the crust upwards. Artemis Corona, however, bears the marks of a kind of plate tectonics. Material may rise in its central region and sink (subduct) in the trough at its rim (Stofan et al. 1992).

About 500 coronae have been counted on Venus. Most of them occur in chains or in groups, mainly near trough systems whose sides move apart.