Venus’s ‘squishy’ outer shell may be resurfacing the planet

Geological activity under Venus’s “squishy” outer shell may be resurfacing our neighbouring planet, keeping its surface youthful and fresh. This is the conclusion of a new study undertaken by scientists with NASA using data from the three-decades-old Magellan mission. The findings may help explain exactly how Venus — a planet around the same size as Earth, and with a similar chemistry — loses heat.

Our planet has a hot core which heats up the surrounding mantle, which in turn carries this thermal energy up to the lithosphere, Earth’s rigid outer layer, where it can be lost to space.

Convection of material within the mantle, meanwhile, serves to drive tectonic processes on the Earth’s surface, keeping a patchwork of continental and ocean plates in motion.

In contrast, our neighbour Venus has no plate tectonics — and thus how it loses its heat and what processes shape its surface have been long-running questions for planetary scientists.

In the new study, NASA researchers have probed this mystery using data on quasi-circular geological features on Venus’s surface known as coronae that were observed by the Magellan spacecraft back in the early nineties.

Taking new measurements of coronae visible in the Magellan images, the team have concluded that the features tend to appear where Venus’s lithosphere is at its thinnest and most active.

Paper author and geophysicist Dr Suzanne Smrekar of NASA’s Jet Propulsion Laboratory in California said: “For so long we’ve been locked into this idea that Venus’s lithosphere is stagnant and thick, but our view is now evolving.”

As the team explains, a thin lithosphere offers less insulation, allowing more heat to escape from Venus’s interior from the buoyant plumes of molten rock within the planet’s mantle.

Enhanced heat flow typically corresponds to increased subterranean volcanic activity — and so the coronae likely reveal locations where geological processes are actively shaping Venus’s surface.

The researchers focussed on 65 previously unstudied coronae that were determined to be up to a few hundred miles across.

They estimated the thickness of the lithosphere at the site of each coronae by measuring the depth of the trenches and ridges around the feature and applying a model of how elastic lithosphere bends.

From this, they determined that, on average, the lithosphere around each coronae is some seven miles thick — much thinner than previous studies have indicated.

Moreover, these regions of Venus’s surface were estimated to have a heat flow that is much greater than the Earth average, suggesting that the coronae are geologically active.

Dr 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.”

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The team’s findings support those of previous studies which suggest that Venus’s surface is relatively young — having been refreshed by volcanic activity.

Scientists have come to this conclusion by counting the number of visible impact craters on the planet, which revealed far less than one would expect for a stagnant surface geology on a planet with no plate tectonics to recycle crustal material.

Dr 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.”

Alongside leading this study, Dr Smrekar is also heading up NASA’s upcoming Venus Emissivity, Radio science, InSAR, Topography, And Spectroscopy (VERITAS) mission, which is expected to launch within the next decade.

VERITAS has been designed to pick up where the Magellan mission left off — albeit bringing to bear higher resolution imaging and significantly lower margins of error.

A state-of-the-art synthetic aperture radar will be used to create global three-dimensional maps of Venus’s topography, while a near-infrared spectrometer will help scientists determine what the planet’s surface is made of.

Alongside this, the VERITAS spacecraft will also be taking measurements of the planet’s gravitational field in order to help probe the structure of Venus’s interior.

Dr Smrekar concluded: “VERITAS will be an orbiting geologist, able to pinpoint where these active areas are, and better resolve local variations in lithospheric thickness.

“We’ll even be able to catch the lithosphere in the act of deforming. We’ll determine if volcanism really is making the lithosphere ‘squishy’ enough to lose as much heat as Earth, or if Venus has more mysteries in store.”

The full findings of the study were published in the journal Nature Geoscience.

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