Evidence for a hotspot Venus - clues from mysterious coronae

The surface of Venus is littered with ring-shaped structures called coronae, whose formation is often linked to underlying mantle plumes. We show how coronae provide unique insights into the present-day geological activity of Venus, and globally map ongoing plume activity on the planet.

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Our neighbouring planet Venus holds key insights into terrestrial planet evolution and early Earth geodynamics. Amongst several spacecraft missions to the planet, NASA's Magellan mission (1989-1994) revealed that geodynamically, Venus is a surprise. A wealth of volcanoes, rifts and mountains cover the planet's surface, despite the apparent absence of Earth-like plate tectonics. To what extent these surface tectonic and volcanic features reflect the current state of the planet's interior, and whether Venus is geologically active today, remain in question. 

Corona structures
 may bear testimony to turbulent processes within Venus. Coronae (Latin for 'crowns', singular corona) are large ring-shaped features on the Venusian surface with traces of tectonic and volcanic activity. They are commonly thought to form by the interaction between a hot mantle plume and the lithosphere, yet the detailed processes involved remain enigmatic. During my MSc thesis project, I systematically ran 3D computer models of plume-lithosphere interactions on Venus to assess the origin and morphological diversity of these corona structures. Building on previous work of corona formation and guided by an excellent team of scientists (Taras Gerya, Laurent Montési and Jessica Munch), I pursued this scientific avenue in the hope of expanding our understanding of Venusian geodynamics. 

Several types of plume-lithosphere interaction dynamics were found to underly distinct types of corona structures at the surface. Most notably, however, the results showed that different corona morphologies represent no­­­t only different styles of plume-lithosphere interaction, but also different stages in evolution: corona structures related to ongoing plume-lithosphere interaction (active) are profoundly different from fossil corona structures (inactive). 

Corona structures on Venus imaged by Synthetic Aperture Radar (left), their topographic signature (middle) and comparison with one of our numerical models (right). The presence of an outer rise and a deep trench at the Aramaiti corona (top) is suggestive of ongoing plume activity, whereas the Thouris corona (bottom) displays an outer rim and inner depression that we ascribe to inactivity. More detail can be found in Gülcher et al. (2020)

But what are the implications of these numerical results? What more can they tell us about nature? These questions naturally arise after having run and analysed a suite of numerical models. It was only during a fruitful discussion at my poster presentation at the AGU Fall Meeting 2018 that it hit me. Could I use these numerical modelling results to individually assess the current activity of large corona structures on Venus, and thereby globally map locations of plume (in)activity on the planet? When I proposed this to my collaborators, they were full of enthusiasm. "That may reach Nature", Laurent said, and I suppose he was right. 

Full of excitement I took on this challenge, despite my MSc thesis project formally being finished and having started a new PhD project (thanks to my supportive supervisors). I set out to investigate the topographic patterns of 133 large coronae on the Venusian surface, using the global data set from NASA's Magellan mission. I identified which structures are currently active, inactive or 'unresolved', guided by the conclusions from our numerical modelling study. This assessment revealed broad regions of ongoing plume activity on the planet, mostly located in the Eistla Regio and in essentially a ring around the planet in the southern hemisphere (covering Themis Regio, Lada Terra and Alpha Regio), as is shown in the Figure below. The full coronae classification dataset has been made freely available

Global distribution of coronae identified as inactive (white circles) or showing ongoing activity (red circles) on Venus. The lines surround proposed areas of plume activity (red) or inactivity (white). In particular, the seemingly active 'belt' in the lower hemisphere sparks intriguing questions about dynamics in the deep interior of Venus. More detail can be found in Gülcher et al. (2020)

These results present new evidence for widespread recent tectonic and magmatic activity on the surface of Venus, supporting team 'geologically active Venus'. The planet's dynamics may be much more akin to Earth-like volcanic and interior processes than originally thought. Moreover, the global distribution of these active coronae may suggest that Venus has a sort of 'ring of fire', like the Earth, only from a different origin. Clearly, how this global distribution reflects the circulation patterns of the deeper interior remains something to explore further. 

With the help of my collaborators and the tough but fair comments by the reviewers, this work is now published in Nature Geoscience. It was a challenging road to get here, but well worth it. I foresee many interesting future studies on this 'hotspot Venus' and the evolution of terrestrial planets in general, and advocate any of the future missions to Venus that are currently on the drawing board. I'll leave you with our key findings visualised on a 3D rotating Venus:

The full article (Corona structures driven by plume-lithosphere interactions and evidence for ongoing plume activity on Venus by A. J. P. Gülcher, T. V. Gerya  L. G. J. Montési and J. Munch) is available at https://www.nature.com/articles/s41561-020-0606-1 

Featured (top) image Credit: Dotted Yeti / Shutterstock.com

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Anna Gülcher

PhD student, Geophysical Fluid Dynamics group, ETH Zürich

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