Science.-Colossal impacts would explain why Venus is not like Earth

12-16-2021 An artist’s rendering of a large early collision on Venus. The new modeling results suggest that high-speed impacts like this could have melted the mantle of Venus, altering its planetary evolution. RESEARCH AND TECHNOLOGY POLICY SOUTHWEST RESEARCH INSTITUTE / SIMONE MARCHI.


A new model suggests that large, high-speed impacts during Venus’ early history could explain the differences between Venus and its rocky sister planet Earth.

The two planets are alike in many ways. They have similar sizes, masses and densities, and are at relatively similar distances from the Sun. However, some key differences, such as habitability, atmospheric composition and plate tectonics, remain unexplained.

High-speed impacts could help explain why Earth is habitable while Venus is not, according to new research presented at the fall meeting of the AGU (American Geophysicial Union).

“At the beginning, at the beginning of the Solar System, the impactors would have been huge,” Simone Marchi, a planetary scientist at the Southwest Research Institute, said in a statement. “If an early impactor had been larger than, say, a few hundred kilometers in diameter, it could have affected the deep interior of a planet, along with its surface and atmosphere. These colossal collisions would affect basically everything about a planet. “.

Recent work by a different research group showed that impactors during Venus’ late accretion phase, around 4.5 to 4 billion years ago, could have hit the planet at much higher speeds, on average, than those that collide. with the Earth. More than a quarter of the collisions with Venus would have occurred at speeds of at least 30 kilometers per second.

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The new research shows that large, high-speed impacts on Venus cause twice the mantle melting as impact-induced melting on Earth. High-speed impactors hitting Venus at a shallow angle would have resulted in the complete melting of the mantle, according to the new research.

When even one of these high-speed massive impactors hit Venus, it would have disrupted and essentially reset the planet’s evolution, according to Marchi. Venus could have gone from a solid rocky body to a molten mess in moments, altering the mineralogy and physical structure of the planet’s interior and surface. Any pre-existing atmosphere would have been largely destroyed and replaced by volatile gases emerging from the melt. A single high-speed impact could have ultimately determined whether or not tectonic plates were formed, which is an important aspect of habitability.

While the large impacts likely struck both Earth and Venus, the latter could have suffered substantially greater melt and disruption due to the high velocity of their impacts, placing the planets on divergent evolutionary paths. For both planets, and the Solar System as a whole, these early collisions had major consequences on their habitability – or lack thereof – today.

“These collisions were responsible for shaping the Solar System. It is not a stretch of the imagination to say that without these processes, we would live in a completely different environment and perhaps we would not be here,” Marchi said. “We need to ask ourselves how much of the planet we live on today was shaped by these early violent events.”

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