To this day, continental drift has been responsible for changes to Earth's surface. Venus, on the other hand, displays a motionless crust, but this was not always the case. Using simulations, planetary researchers at the German Aerospace Center (Deutsches Zentrum für Luft- und Raumfahrt; DLR) have now discovered that, in the past, the surface of Venus was probably quite hot, and consequently dynamic.
"Our calculations have given us a glimpse into the past of Venus, when the surface temperature was significantly higher than today’s 470 degrees Celsius. We have encountered an amazing effect," says Lena Noack, a post-graduate student at the DLR Institute of Planetary Research in Berlin-Adlershof. "Venus' crust is not rigid at such temperatures. Instead, it starts moving in certain places. It stretches and elongates without cracking, like a chocolate bar softened by the heat of summer." The particularly high temperatures on Venus were the result of a massive greenhouse effect that later weakened. "A particularly strong greenhouse effect can overcome the rigidity of a planet’s surface. This could be what happened during the course of Venus’ history," explains the planetary researcher. The partial movement of Venus’ crust even enabled the interior to release more heat into the atmosphere, leading to a reduction in the temperature of the planet’s mantle much like the cooling of Earth’s interior by plate tectonics.
Extremely slow movement
Movements in Venus' crust probably occurred extremely slowly. "The speed obtained in our calculations was of just a few millimetres a year," says Doris Breuer, Head of the Planetary Physics Department at the DLR Institute of Planetary Research. "Earth's tectonic plates move relative to one another at a rate of several centimetres per year." Besides the known plate tectonics on Earth and the rigidity of Mars' crust, the planetary researchers have found a third variant. "We refer to this process as 'local mobilisation' because Venus’ crust is very slowly being moved by the underlying layer in just a few places," explains Noack.
'Planetary Evolution and Life' research alliance
The research results published in the scientific journal Icarus under the title 'Coupling the Atmosphere with Interior Dynamics: Implications for the Resurfacing of Venus' came about as part of the 'Planetary Evolution and Life' research alliance. The alliance was sponsored by the Helmholtz Association of German Research Centres (Helmholtz-Gemeinschaft Deutscher Forschungszentren; HGF) and is headed by the DLR Institute of Planetary Research. "Under this alliance, over 150 scientists from non-university research facilities and from German and international universities are jointly researching planetary evolution and the subsequent conditions under which life emerges and survives," says Tilman Spohn, Director of the DLR Institute of Planetary Research and scientific coordinator of the alliance. "In order to research these subjects more comprehensively, we have created a network of representatives from the various natural sciences, such as physicists, geologists and biologists." The research alliance was initiated in 2008 and will run for five years.