Study suggests Venus may have swallowed its moon

A California astrophysicist has presented a new theory that could explain why Venus, the planet most similar to Earth in size, mass and structure, does not have a moon. It could be said to be a case of celestial cannibalism.

Venus's extremely slow rotation around its axis would mean that any natural satellite that may have once orbited the planet was doomed to gradually approach it and eventually be destroyed in a catastrophic collision.

That's the theory put forward by scientists at the University of California, Riverside, and published in The Astrophysical Journal. It represents a departure from previous explanations for why Venus, the second planet from the Sun, has no natural satellite, Reuters reports.

"If it had a moon, and it probably did at some point, it couldn't have held on to it," astrophysicist Stephen Crane, the study's lead author, told Reuters. "That moon would have crashed into the planet in a relatively short period of time."

Crane said that data from computer models based on planetary physics, which simulated the gravitational dynamics of hypothetical Venusian moons of different sizes, showed that they would all suffer the same fate - sooner or later they would fall back onto their home planet.

Such a postulated event in which Venus "swallowed" its moon likely occurred during the first billion years of that planet's history, which, like the rest of the solar system, is about 4,5 billion years old, Crane said.

Scientists previously assumed that Venus, known as Earth's "twin," either never had its own moon, or it did have one but it was destroyed in a powerful impact from another celestial body.

Earth rotates much faster than Venus

A study by the University of California, Riverside, which looked at the dynamics of the relationship between the Earth and the Moon, showed that the planet's rotation speed is a key factor.

Unlike Venus, which takes 243 Earth days to rotate once on its axis - slightly longer than it takes to orbit the Sun - Earth rotates on its axis in 24 hours, or more than 200 times faster than Venus, Crane said.

The transfer of energy from the Earth's faster rotation is gradually pushing the Moon further and further away from our planet, causing it to recede at a rate of four centimeters per year. This rate was precisely measured by reflectors left on the lunar surface by the Apollo 11 astronauts in 1969.

Venus, the third brightest object in our sky after the Sun and Moon, is very important to scientists trying to learn more about Earth's past, but also its future.

Similar in rocky structure to Earth but slightly smaller, Venus is enveloped in a thick and toxic atmosphere that has caused an uncontrolled greenhouse effect. As a result, the temperature on its surface reaches as high as 471 degrees Celsius, which is enough to melt lead.

While there is no evidence that Venus ever had a moon, it is unlikely that it somehow avoided a violent collision with another protoplanet in its early history, like the one thought to have led to the formation of Earth's Moon, Crane said.

In the early days of the inner solar system, numerous large rocky bodies moved through space and collided with each other, and Venus probably suffered more such impacts than Earth because it is closer to the Sun.

Scientists hope to uncover more of Venus' secrets thanks to two upcoming NASA missions, DAVINCI+ and VERITAS, scheduled for launch in the late 2020s or early 2030s, which will study the planet's atmosphere and geological features.