Since Venus and Earth are both rocky planets with roughly the same size and chemistry of their rocks, they should be losing their internal heat to space at a similar rate. Yet Venus’s heat flow process has remained a mystery. It is known how the earth loses heat. A new study of how Venus is cooling has been conducted using three decades of data from NASA’s Magellan mission. The results suggest that thin sections of the planet’s upper layer may hold the key.
Our planet’s hot core heats the surrounding mantle and transfers that heat to the lithosphere, the planet’s rigid outer layer of rocky material. The highest part of the mantle cools down because the heat is lost to space. This mantle convection keeps a jumble of moving plates moving, which also drives surface tectonic processes. Because Venus has no tectonic plates, planetary scientists have long wondered how it loses heat and what forces shape its surface.
The research drew on studies of Venus’ 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 new measurements of the coronae observed in the Magellan images.
Suzanne Smrekar, a senior research scientist at NASA’s Jet Propulsion Laboratory in Southern California, said: “We’ve been stuck for so long with the idea that Venus’ lithosphere is stagnant and thick, but our picture is now evolving.”
The study focused on 65 previously unstudied coronae with a maximum size of several hundred kilometers. They assessed the depth of the gullies and ridges that surround each corona to determine the thickness of the lithosphere around it. They found that ridges are closer together in areas where the lithosphere is more elastic, or flexible.
They found that the lithosphere around each corona averages about 7 miles (11 kilometers) thick, which is significantly smaller than previous 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 Earth, coronae may be geologically active.
Smrekar said, “While Venus has no terrestrial tectonics, these areas of thin lithosphere appear to release significant amounts of heat, similar to areas where new tectonic plates form on Earth’s seafloor.”
Planetary scientists count the number of observable 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 with molten rock from volcanoes on a tectonically active planet like Earth. Venus should be covered in ancient craters with no tectonic activity or regular 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 that the youthful appearance of Venus’ surface is likely due to volcanic activity, which is the cause of regional resurgence today. This finding is supported by the new research indicating higher heat flow in coronae regions – a state Earth’s lithosphere resembled in the past.
Smrekar said, “What’s interesting is that Venus offers a window into the past to help us better understand what Earth looked like more than 2.5 billion years ago. It’s in a state that is predicted to occur before a planet forms tectonic plates.”
Magazine reference:
- Smrekar, SE, Ostberg, C. & O’Rourke, JG Earth-like lithospheric thickness and heat flow on Venus consistent with active rifting. Wet. geosci. 16, 13–18 (2023). DOI: 10.1038/s41561-022-01068-0
