Novae and Coronae

This week’s image shows Yavine Corona, a volcanic feature near the equator of Venus. The description of this image on the NASA photojournal describes it as “a 500-km-wide asymmetric feature at latitude 5 degrees S., longitude 248.5 degrees; looking northeast”. This gives us a sense of the scale of the feature, a huge irregularly shaped dome with extensive fractures.  The 3D view was made by combining synthetic aperture radar data with elevation information, all from the Magellan Spacecraft. 

They don’t state to what extent the vertical scale has been exaggerated in this image, but it certainly looks as though it has been, this is particularly the case with the smaller dome to the right of centre, which has the characteristic features of a gentle hill where the “relief” has been exaggerated. This is common practice when presenting topographic features of this scale. It helps to pick out subtle details which would otherwise be too small to detect with the naked eye. We are also used to seeing hills and mountains from below, rather than from the sky. What would look like a steep slope from the ground, can often seem far too shallow when seen from a different angle, especially when the feature is hundreds of kilometres across. Some structures like shield volcanoes are very tall, but don’t actually have the steep slopes we associate with other types of mountain. This means that we often need to exaggerate the image in order to correctly interpret what we are seeing. 

The word Corona means “crown” in Latin, and continues the theme of planetary scientists naming things based on their approximate appearance. Coronae are vaguely “crown like” volcanic features, consisting of a heavily fractured plateau, often surrounded by a deep trench. The whole edifice is riddled with concentric and radial fractures. Coronae are believed to form through the upwelling of plumes of Magma. These partially melt the surface, causing collapse and faulting. However the exact mechanism is still being debated. There are 513 such features on Venus, and similar structures have been observed on Miranda, one of the moons of Uranus. The features on Miranda would have formed through the upwelling of molten ice, but are otherwise quite similar in form.  

Coronae are not the only volcanic feature in this image. Yavine Corona also exhibits two “novae”. These are circular hills around 100-300 km in diameter. They are named for the star like fractures that radiate out from their centre. Novae may be an early stage in the development of the larger coronae. The image below shows a close up of the southern of the two structures. The NASA photojournal notes that this feature is approximately 100 km across. Further data is needed to determine precisely how novae and coronae form, and whether one feature develops into the other. 

Image Credits: NASA/JPL/USGS

https://photojournal.jpl.nasa.gov/catalog/PIA00098

https://photojournal.jpl.nasa.gov/catalog/PIA00150