It feels like Venus has been in the news a lot lately, which is surprising because up until last year, we mostly ignored our sister planet. The clouds are too thick, the surface is too hot, the air is too toxic, etc. Now we’re talking about sending more missions there than ever before, and the science coming out from a variety of work being done is being noticed by the press. Thank you, phosphine, whether or not you’re really there.

In our first planetary story today, a new paper published in Nature Astronomy uses the planet’s largest known crater to analyze the thickness of Venus’s lithosphere, that outer shell of crust. Here on Earth, our crust is considered thin. It is broken into plates that ride on the top of the mantle, which is warm and plastic. This configuration is why we have volcanoes and earthquakes — our planet is constantly changing, creating new land and destroying old crust.

Venus also has volcanoes. It is suspected they may even have been active in the recent geological past. But that thick atmosphere I mentioned earlier prevents us from directly imaging the surface to really analyze the rocks. In our interview with Dr. Darby Dyar last week, we talked about how there are spectroscopic windows future missions might be able to use to “see” that surface more clearly. In the meantime, we have to use the radio imaging data currently available to make sense of Venus. And one of the questions we’re trying to answer is whether or not Venus had a primitive form of plate tectonics that could account for those volcanoes.

Scientists used radio images of Mead Crater, the largest on Venus, to generate computer models that allowed them to analyze the thickness of the lithosphere. The crater is surrounded by two rings of ridges, and their final position is an indicator of the thickness and thermal gradient of the rocks that were impacted. Basically, it’s harder to deform colder rocks than warmer ones, and those characteristics determine the distance at which the impact rings formed.

What the team found was that the crust is thicker on Venus with a lower thermal gradient than on Earth and unlikely to have had similar plate tectonics. Graduate student and lead author Evan Bjonnes explains: You can think of it like a lake freezing in winter. The water at the surface reaches the freezing point first, while the water at depth is a little warmer. When that deeper water cools down to similar temperatures as the surface, you get a thicker ice sheet.

The Mead impact is about a billion years old, which means Venus hasn’t had active tectonics in at least that long, and that result changes what we thought happened in Venus’s past. We need those new missions to Venus, please.

More Information

Brown University press release

“Estimating Venusian thermal conditions using multiring basin morphology,” E. Bjonnes, B. C. Johnson and A. J. Evans, 2021 January 28, Nature Astronomy