Venus’ squishy lid
When it comes to size and radiogenic heat (which is generated by the radioactive decay of elements within a planet’s mantle and crust), Venus is the twin of Earth. This is, however, where their similarities end. Venus and Earth differ geologically, and one key aspect has left a gap in the ongoing geodynamic puzzle that is Venus – plate tectonics.
Plate tectonics, in particular areas of active extension where the crust is pulling apart, like at spreading ridges and behind subduction zones, prevent Earth from overheating by allowing it to lose its radiogenic heat to space. In contrast, although Venus has tectonic activity in the form of volcanoes and mountains, it doesn’t have tectonic plates across its surface. This raises the question of how Venus loses its radiogenic heat.
Suzanne Smrekar at the Jet Propulsion Laboratory, California, USA, and colleagues investigate this heat loss mystery. Using altimetry data collected by the Magellan spacecraft during NASA’s mission to Venus in the early 1990s, the team estimate the thickness of Venus’ crust beneath specific volcano-tectonic features on the planet’s surface, termed coronae. From these estimates, they calculate the average amount of radiogenic heat lost by Venus to space.
They find that although Venusian crust has a similar general thickness to Earth’s crust, the thickness varies across the planet; coronae in particular typically form on areas of thin lithosphere. As a result, heat flow differs globally. However, Venus loses more radiogenic heat than Earth overall, at rates comparable to areas of highest heat loss on Earth. The findings support the idea that Venus loses radiogenic heat via abundant intrusive magmatism – the so called ‘squishy lid’ model – implying that Venus may reflect the Archaean Earth before plate tectonics evolved.
Nature Geoscience (2022 In Press); https://doi.org/10.1038/s41561-022-01068-0