30 years of NASA's Magellan mission may finally solve how Venus cools

Given 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. How Earth loses its heat is well known, whereas Venus' flow process remains a mystery.

According to a news release from NASA, new research has taken a fresh look at how Venus cools using data from the NASA Magellan mission that spans three decades and discovered that thin parts of the planet's uppermost layer might provide an answer.

How does Venus, the hottest planet in the solar system, lose its heat?

The study investigated the mystery using observations made by the Magellan mission in the early 1990s of geological structures on Venus known as coronae.

Researchers found that coronae typically occur where the planet's lithosphere is thinnest and most active by taking fresh measurements of the coronae observed in the Magellan photos.

"For so long, we've been locked into this idea that Venus' lithosphere is stagnant and thick, but our view is now evolving," said lead author Suzanne Smrekar, a senior research scientist at NASA's Jet Propulsion Laboratory in Southern California.

Essentially, a thin lithosphere permits more heat to escape from the planet's interior through buoyant plumes of molten rock rising to the outer layer. Usually, greater heat flow is accompanied by increasing volcanic activity at depth. Hence, coronae probably indicate areas where Venus' surface is currently being shaped by active geology.

Sixty-five previously unstudied coronae that were up to a few hundred miles broad were the main focus of the study. 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 also found that, on average, the lithosphere surrounding each corona is roughly 7 miles (11 kilometers) thick- substantially thinner than prior studies suggest. 

The researchers applied a computer model of how an elastic lithosphere bends. Significantly, the predicted heat flow in these locations is higher than the average for Earth, indicating that coronae are geologically active.

"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," added Smrekar.

The complete study was published in Nature Geoscience and can be found here.

Study abstract:

Venus is Earth’s twin in size and radiogenic heat budget, yet it remains unclear how Venus loses its heat absent plate tectonics. Most Venusian stagnant-lid models predict a thick lithosphere with heat flow about half that of Earth’s mobile-lid regime. Here we estimate elastic lithospheric thickness at 75 locations on Venus using topographic flexure at 65 coronae—quasi-circular volcano-tectonic features—determined from Magellan altimetry data. We find an average thickness at coronae of 11 ± 7 km. This implies an average heat flow of 101 ± 88 mW m−2, higher than Earth’ s average but similar to terrestrial values in actively extending areas. For some locations, such as the Parga Chasma rift zone, we estimate heat flow exceeding 75 mW m−2. Combined with a low-resolution map of global elastic thickness, this suggests that coronae typically form on thin lithosphere, instead of locally thinning the lithosphere via plume heating, and that most regions of low elastic thickness are best explained by high heat flow rather than crustal compensation. Our analysis identifies likely areas of active extension and suggests that Venus has Earth-like lithospheric thickness and global heat flow ranges. Together with the planet’s geologic history, our findings support a squishy-lid convective regime that relies on plumes, intrusive magmatism and delamination to increase heat flow.