This article has been reviewed according to Science X's editorial process and policies. Editors have highlighted the following attributes while ensuring the content's credibility: Scientists have long speculated why Venus, with a size, mass and structure similar to Earth's, doesn't have a moon. New UC Riverside research shows that our hungry twin likely swallowed it.
In the past, scientists theorized that Venus possibly had a moon that was hit by something massive, obliterating it. Other theories centered on the idea that Venus never underwent a collision that formed a moon in the first place. The new research, published in The Astrophysical Journal, shows that neither theory fits.
"My study shows Venus didn't require a catastrophe to arrive at what we can see today," said UCR astrophysicist and lead author Stephen Kane. "It turns out the gravity of the planet itself combined with the rate at which it spins naturally caused the moon to collapse on top of it." Scientists can precisely measure the distance between Earth and the moon because NASA's Apollo 11 landing left mirrors there. "We know that the moon is slowly moving away from the planet, at a rate of around four centimeters (1.6 inches) per year," Kane said.
This distancing, Kane said, is happening because Earth completes a relatively fast rotation every 24 hours. The energy from this spinning gets transferred to the moon, causing it to move away. Venus has the opposite situation.
It takes the planet 243 Earth days to complete a single rotation. Rather than gradually moving away, the slow spin and the planet's gravity would cause a moon to spiral inward toward a collision. To test this idea, Kane developed computer models based on the physics of how planetary bodies interact through gravity.
He first reproduced the evolution of Earth and its moon to make sure the model accurately represented a known system. Then he varied Venus' rotation rate and the size of its hypothetical moons, testing moons with masses ranging from half to 10 times the mass of Earth's moon. In most simulations, the result was the same: The moon crashed into Venus.
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