Venus May Have Devoured Its Moon, New Theory Suggests

A California-based astrophysicist has put forth a new theory to explain the absence of a moon orbiting Venus, the planet most similar to Earth in size, mass, and structure. The hypothesis suggests that Venus may have consumed its own moon due to its extremely slow rotation.

The theory, presented by scientists at the University of California, Riverside, and published in The Astrophysical Journal, posits that any natural satellite that may have once orbited Venus would have gradually spiraled closer to the planet and ultimately been destroyed in a cataclysmic collision. This offers a new perspective on why Venus, the second planet from the sun, lacks a lunar companion.

"If it had a moon, and it likely did at some point, it could not have kept it," said astrophysicist Stephen Krane, the study's lead author, in a statement. "That moon would have crashed down on the planet in a relatively short time scale."

Krane explained that computer models simulating the gravitational mechanics of hypothetical Venusian moons of various sizes consistently showed them meeting the same fate: collapsing into their parent planet. This moon-swallowing event, according to Krane, likely occurred within the first billion years of Venus's history, which, like the rest of the solar system, dates back approximately 4.5 billion years.

Previous scientific explanations for Venus's lack of a moon included the possibility that it never acquired one or that any existing moon was obliterated by a massive impact from another celestial object. The new UC Riverside study, however, emphasizes the critical role of planetary rotational speed.

In contrast to Venus, which takes 243 Earth days to complete a single rotation (slightly longer than its orbit around the sun), Earth spins on its axis every 24 hours. This makes Earth's rotation more than 200 times faster than Venus's, Krane noted.

This rapid rotation of Earth is gradually pushing our moon farther away, causing it to recede at a rate of 4 centimeters (1.6 inches) per year, a phenomenon precisely measured by mirrors left on the lunar surface by Apollo 11 astronauts in 1969.

Venus, often referred to as Earth's "twin" due to its similar rocky structure and slightly smaller size, is enveloped in a thick, toxic atmosphere that has resulted in a runaway greenhouse effect. This has led to surface temperatures as high as 880 degrees Fahrenheit (471 degrees Celsius), hot enough to melt lead.

While direct evidence of a Venusian moon's existence is lacking, Krane suggests it is improbable that Venus, in its early formation, escaped the kind of planet-altering collision believed to have formed Earth's moon. The early inner solar system was a chaotic environment filled with large celestial objects colliding, and Venus, being closer to the sun, may have experienced more such impacts than Earth.

Future research into Venus is planned with two forthcoming NASA missions, DAVINCI+ and VERITAS, scheduled for launch in the late 2020s or early 2030s, aimed at studying the planet's atmosphere and geological features.