…if indeed it ever had a moon at all. BBC takes up the story.
Study says that if Venus ever did have a moon, the planet’s spin and gravity would cause the moon to be swallowed by it
Earth and Venus orbit the Sun side by side and, compared to the icy, gassy giants of the outer Solar System, the two planets are relatively similar.
So why is it that Earth has a Moon – indeed, our other neighbour Mars has two – but Venus has none?
Scientists have come up with an intriguing new theory. They say Venus ate its own moon.
The story of Venus’s lost moon
Earth’s Moon is thought to have formed when a small planetary body – name Theia – smashed into our home planet during the more chaotic early days of the Solar System.
Scientists have previously suggested that Venus may have had a moon at one time, but the Venusian satellite was obliterated when it got hit by a much bigger body.
Another theory regarding Venus’s lack of a moon suggests Venus simply never experienced a collision – like Earth did – that formed a moon in the first place.
Gravity always wins
A team of scientists at the University of California, Riverside in the USA have published a study in The Astrophysical Journal that says neither of the theories explain Venus’s sans-satellite status.
“My study shows Venus didn’t require a catastrophe to arrive at what we can see today,” says UCR astrophysicist and lead author of the study Stephen Kane.
“It turns out the gravity of the planet itself, combined with the rate at which it spins, naturally caused Venus’s moon to collapse on top of it.”
Key to this theory is the fact that Earth’s Moon is gradually floating away from it, year by year.
Scientists know this because the Apollo astronauts left mirrors on the lunar surface that scientists can bounce lasers off to accurately measure the distance from Earth to the Moon.
The results show that the Moon is moving away from Earth at a rate of 3.8cm (1.5 inches) a year.
“We know that the Moon is slowly moving away from Earth at a rate of around 4cm per year,” Kane says.
This is happening, Kane says, because Earth spins so fast – once every 24 hours.
The energy from this rapid rotation is transferred to the Moon, causing it to move away from Earth.
But Venus, the scientists say, is the exact opposite. It takes Venus 243 Earth days to complete a single rotation.
So rather than moving away, that slow spin combined with Venus’s gravity would cause a moon to spiral inward.