High-speed impacts on Venus early in its history could help explain why the planet isn’t habitable today.
It remains somewhat of a mystery why Venus and Earth took such divergent paths, despite being fairly similar in size at relatively similar distances from the sun. Various explanations, such as Venus never cooling enough to condense oceans, have previously been put forward.
and at the Southwest Research Institute in Boulder, Colorado, examined a different possibility. As material swirled around the early solar system, around 4.5 to 4 billion years ago, both Earth and Venus were probably hit by large objects. One of these, dubbed Theia, is thought to have helped form the moon, after a collision with Earth sent a chunk of material into space.
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Previous modelling has shown, however, that owing to Venus being closer to the sun’s immense gravity it experienced higher-velocity impacts than Earth – an average of 23 kilometres per second, compared with 19 kilometres per second. A quarter of these may have been extremely fast, at more than 30 kilometres per second.
Marchi and Rufu’s research found that these impacts could have turned as much as 80 per cent of Venus’s mantle molten, preventing it from following the same path as Earth. “We believe these energetic collisions could trigger interesting processes that would make the planet what it is today,” says Marchi. “It would melt the planet and drive water into the atmosphere.”
The research was presented on 16 December at a meeting of the American Geophysical Union in New Orleans.
Upcoming missions to Venus, such as three missions planned by NASA and the European Space Agency, could determine if this idea is correct. They could search the atmosphere for trace elements of gases from a molten mantle, or seek evidence of a late magma ocean on Venus.
The findings could have implications for exoplanets, too, even those in supposed habitable zones where liquid water could exist. “If you are in a [region] where there are collisions at high speeds, that could completely reset a planet,” says Marchi.
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