We are trying to understand why Venus and Earth ended up such vastly different worlds. After all, they are roughly the same size, mass, and density, and their distances from the Sun aren’t that different. But their atmospheres and plate tectonics are not the same, and that doesn’t even bring into account the weirdly slow rotation of Venus.

In new research presented at the American Geophysical Union’s Fall Meeting, scientists modeled how large, high-speed impacts in our early solar system might have affected Venus differently from Earth. Planetary scientist Simone Marchi explains: Early on, in the beginning of the Solar System, the impactors would have been immense. If an early impactor was 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 basically affect everything about a planet.

Basically, the higher speed impacts lead to twice as much melting of Venus’ mantle than the impacts that hit Earth. And impacts to Venus that came in at shallow angles would have completely melted the mantle. All that sudden melting affected the mineralogy and structure of the planet, and the atmosphere would have been blasted away for the most part. Then the volatile gases from the interior would have replaced that atmosphere, and suddenly, you have a very different world from Earth.

Thank goodness we have not one, not two, but three missions heading to Venus to help us understand a world we sometimes refer to as Earth’s twin. Sister planets they may be, but they are fraternal twins at best.

More Information

AGU press release