Why Venus is so “hot-blooded”.

Presentation video for the study. ©Southwest Research Institute

What is the secret of our planetary neighbor’s “fiery temper” and “youthful looks”? A model simulation now shows: Compared to Earth, Venus was hit by harder impacts in its early development history. This led to a particularly hot core, which caused extensive volcanism and the associated surface renewal processes, the scientists explain.

Initially, a loose disk of material orbited the young sun, then the material agglomerated into larger and larger structures – the planets of our solar system were formed. This also formed two rocky planets that have a lot in common, but still differ significantly. “One of the mysteries of the inner Solar System is that despite their similar sizes and densities, Earth and Venus function in strikingly different ways, particularly affecting the processes that move materials through the planets,” says lead author Simone Marchi of the Southwest Research Institute (SwRI) in Boulder.

Why so different?

In the case of the earth, the dynamic processes are shaped by plate dynamics: the earth’s crust is divided into large pieces that seem to float on the molten underground. In doing so, they collide or overlap, causing mountains to fold up and, in places, molten material to penetrate to the surface. But Earth’s volcanism is modest compared to the record holder for “hot-bloodedness” in the solar system: Venus has more than 80,000 volcanoes – 60 times more than Earth. The volcanoes of Venus are not located on plate edges, because our planetary neighbor does not have them: it has a continuous surface that is perforated by the numerous volcanoes. Their lava flows have led to the comparatively young surface structures of Venus, according to earlier studies.

So far, however, it has not been possible to explain convincingly why Venus exhibits such intense volcanism. As part of their study, Marchi and her colleagues have now used model simulations to specifically investigate the extent to which impacts of planetary building blocks could have played a role in the early history of Venus. The multidisciplinary team developed collision models based on known data and combined them with simulations of geodynamic processes in order to assess the consequences of the impacts for the long-term evolution of Venus.

Consequences of a particularly “wild” youth

As the team reports, their results now demonstrate a significant effect of the early bombardment: “Our new modeling makes it plausible that particularly high-energy collisions on Venus led to the long-lived volcanism and young surface age of Venus,” summarizes the senior author Jun Korenaga of Yale University in New Haven. “The tremendous volcanic activity is driven by a very hot core, which leads to violent internal melting processes,” says the scientist. The team explains that the hard impacts on Venus compared to Earth have to do with its slightly more inward orbit. Because both planets were created in the same neighborhood when the lumps of matter collided with each other and gradually united to form the two rocky planets. But the subtle differences in the distances of Earth and Venus from the Sun clearly shaped the impact processes.

As the researchers explain, the planetary building blocks crashed into Venus with more force because it moves faster around the sun than Earth. In addition, impactors probably also whizzed into the young planets, which had entered the interior of the solar system from outside the Earth’s orbit. According to the scientists, they had a particularly large amount of kinetic energy. “The high impact velocities then led to a particularly intense silicate melt,” says co-author Raluca Rufu from SwRI. “This created a very hot core and a mantle of molten materials,” says the scientist. This apparently shaped the subsequent geophysical evolution of Venus, the team explains. “If you integrate the energetic impact scenarios into model simulations, the extent of the volcanism on Venus can be easily calculated,” says Korenaga.

With regard to their research topic, the researchers are now looking forward to the research missions currently planned: Both NASA and the European Space Agency ESA want to send new probes to Venus, which are intended to target volcanism, among other things. “There is a lot of interest in Venus at the moment,” says Marchi. “Our results can now benefit the upcoming missions and the mission data could in turn help to confirm them,” says the scientist.

Source: Southwest Research Institute, Article: Nature Astronomy, doi: 10.1038/s41550-023-02037-2

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