Because Venus and Earth are both rocky planets with roughly the same size and chemistry of their rocks, they should be losing their interior heat to space at a similar rate. Yet, Venus’ heat flow process has remained a mystery. It is well-known how Earth loses heat. A new investigation into how Venus cools has been conducted using three decades of data from NASA’s Magellan mission. The results suggest that thin regions of the planet’s topmost layer may hold the key.
Our planet’s hot core heats the surrounding mantle, transferring that heat to the lithosphere, the planet’s stiff outer layer of rocky material. The highest part of the mantle cools due to the heat being lost to space. This mantle convection keeps a jumble of movable plates in motion, which also powers tectonic processes on the surface. As Venus lacks tectonic plates, planetary scientists have long wondered how it loses heat and what forces form its surface.
The investigation used studies of Venus’s coronae, roughly round geological structures, made by the Magellan probe in the early 1990s. Scientists concluded that coronae typically occur where the planet’s lithosphere is weakest and most active by taking fresh measurements of the coronae observed in the Magellan photos.
Suzanne Smrekar, a senior research scientist at NASA’s Jet Propulsion Laboratory in Southern California, said, “For so long, we’ve been locked into this idea that Venus’ lithosphere is stagnant and thick, but our view is now evolving.”
The study concentrated on 65 previously unstudied coronae with a maximum size of a few hundred kilometers. They assessed the depth of the trenches and ridges encircling each corona to determine the thickness of the lithosphere surrounding them. They discovered that ridges are more tightly spaced apart in regions where the lithosphere is more elastic or flexible.
They found that, on average, the lithosphere surrounding each corona is roughly 7 miles (11 kilometers) thick, which is substantially smaller than prior studies suggest. They applied a computer model of how an elastic lithosphere bends. Since the predicted heat flow in these areas is higher than the norm for the Earth, coronae may be geologically active.
Smrekar said, “While Venus doesn’t have Earth-style tectonics, these regions of thin lithosphere appear to be allowing significant amounts of heat to escape, similar to areas where new tectonic plates form on Earth’s seafloor.”
Planetary scientists count the number of discernible impact craters on a celestial body’s surface to determine how old the surface material is. Impact craters are erased by the subduction of continental plates and covered by molten rock from volcanoes on a tectonically active planet like Earth. Venus should be covered in old craters with no tectonic activity or regular churn of Earth-like geology. But, scientists can determine how old the surface of Venus is by calculating how many craters there are on the planet.
Recent studies suggest the youthful appearance of Venus’ surface is likely due to volcanic activity, which drives regional resurfacing today. This finding is supported by the new research indicating higher heat flow in coronae regions – a state Earth’s lithosphere may have resembled in the past.
Smrekar said, “What’s interesting is that Venus provides a window into the past to help us better understand how Earth may have looked over 2.5 billion years ago. It’s in a state that is predicted to occur before a planet forms tectonic plates.”
- Smrekar, S.E., Ostberg, C. & O’Rourke, J.G. Earth-like lithospheric thickness and heat flow on Venus consistent with active rifting. Nat. Geosci. 16, 13–18 (2023). DOI: 10.1038/s41561-022-01068-0