Simulations show how Venus “ate” its own satellite

Venus, a planet often called Earth's "sister" because of its similar size, mass, and composition, may be hiding a dark secret: It may have swallowed its own moon. Unlike Earth, which has a powerful moon, Venus and Mercury are the only planets in the solar system that don't have natural satellites. A new study based on modeling offers an explanation for why Venus may not have been so lucky with a moon.

Lost opportunity to form a satellite

Scientists have long wondered whether Venus has always lacked a moon, or whether it once had one but later lost it. A team of researchers led by Stephen R. Kane of the University of California, Riverside, created a complex simulation to test a hypothesis about the fate of a possible moon of Venus.

“Venus is Earth’s ‘sister,’ and they are nearly identical in size, mass, and composition. However, Earth has a large moon, while Venus has no captured moon, not even a small one,” Kane notes. He adds that Venus, like Earth, has certainly experienced massive collisions that could have led to the formation of the moon.

Gravitational struggle and inevitable death

The simulations took into account the gravitational interactions between Venus, a hypothetical moon, and the Sun over billions of years. It turned out that in most cases, a Venusian moon would not have been able to safely drift away, as our Moon does. Instead, the simulations showed that the moon, as it orbited Venus, would eventually change course and spiral toward the planet, where it would be torn apart by its powerful gravity.

Interestingly, the more massive moon was destroyed more quickly because it was more efficient at "pulling" Venus's rotational energy, accelerating its own destruction. The only scenario for the moon's survival was that Venus rotated very quickly (a day lasted less than 12 hours) and the moon itself was not very massive, about the size of our Moon. However, such conditions probably did not correspond to the realities of early Venus.

Source: https://www.space.com/astronomy/venus/did-venus-eat-its-own-moon