High-speed impacts may have shaped the story of Venus – and explain why it is uninhabitable


New modeling suggests rapid collisions could explain why Earth is habitable while Venus is not. Credit: Southwest Research Institute / Simone Marchi & Raluca Rufu

New modeling suggests rapid collisions could explain why Earth is habitable when ">Venus is not.

New modeling suggests that large, high-speed impacts early in Venus’ history could reconcile the differences between Venus and its rocky sister planet Earth.

The two planets are similar in many ways. They have similar sizes, masses, and densities, and they are at relatively similar distances from the Sun. Yet 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 AGU’s fall 2021 meeting.

“In the beginning, at the start of the solar system, the impactors would have been immense,” said Simone Marchi, a planetologist at the Southwest Research Institute, who presented the study on Thursday, December 16, 2021. “If an early impactor was greater than, say, a few hundred kilometers in diameter, it could have affected the deep interior of a planet, as well as its surface and atmosphere. These colossal collisions would fundamentally affect everything on a planet. “

An example of a smoothed particle hydrodynamic impact simulation of a large planetesimal hitting a Venus-like planet. The middle and right panels show Venus 1 hour and 11 hours after impact. The colors indicate the temperature. Credit: South West Research Institute / Simone Marchi and Raluca Rufu.

Recent work by another research group has shown that impactors during the late accretion phase of Venus, around 4.5 to 4.0 billion years ago, could have struck the planet at much higher speeds, on average, than those colliding with Earth. More than a quarter of collisions with Venus are believed to have occurred at speeds of at least 30 kilometers per second (approximately 67,100 miles per hour).

The new research shows that large, high-speed impacts on Venus result in twice as much mantle melting as impact-induced melting on Earth. High-speed impactors hitting Venus at a low angle would have caused the mantle to completely melt, new research shows.

According to Marchi, even if just one of these massive high-speed impactors hit Venus, it would have interrupted and essentially reset the evolution of the planet. 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 formed, which is an important aspect of livability.

While large impacts likely struck both Earth and Venus, the latter could have experienced substantial melting and disturbance due to the high speed of its impacts, placing the planets on divergent evolutionary paths. For both planets and the solar system as a whole, these early collisions had big consequences for their habitability – or lack thereof – today.

“These collisions shaped the solar system. It is not a stretch of the imagination to say that without these processes we would be living in a completely different environment, and maybe we wouldn’t be here, ”Marchi said. “We must ask ourselves to what extent the planet we live on today was shaped by these early violent events.”

Meeting: American Geophysical Union Fall 2021 Meeting


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