Does Venus have a Moon?
No, Venus does not have a moon – not even a small one. Venus isn’t alone in being moonless; its neighbouring planet, Mercury, also has no moons. These are the only two planets in the Solar System without their own little worlds orbiting them.
Scientists aren’t sure why Venus doesn’t have a moon, but they have a few ideas. Some even suggest that Venus may have had a moon in its distant past, but somehow lost it. That was rather careless of it, wasn't it?
Moons are rocky objects that orbit planets, and they can form in a few different ways:
- They Form with the Planet (Regular Moons): Some moons form alongside their planets from the same materials that created the planet itself. These are called regular moons and tend to have circular orbits that follow the planet's rotation. Jupiter’s Galilean moons and Saturn’s Titan are examples of regular moons.
- They are captured by the Planet (Irregular Moons): A planet’s gravity can capture a nearby object, such as an asteroid, which then begins to orbit the planet. These are known as irregular moons and usually have more elliptical, tilted, or retrograde (backward) orbits. Most captured moons are small, but Neptune’s moon Triton is a large irregular moon.
- Collision Debris: When objects like asteroids collide with a planet or its moons, or moons collide with each other, the debris can stay in orbit and eventually form new moons.
- Giant Impact: A large object might crash into a planet, breaking off a huge chunk. Earth’s moon is believed to have formed this way, when a Mars-sized object collided with Earth billions of years ago.
For whatever reason, none of these things happened to Venus - or to Mercury for that matter. But there may be other reasons why neither planet has a moon. I think this calls for a new box. Shall we go for a blue one, Bobsdog?
Now that we know why other planets have moons, what might prevent Venus from having one? Here are a few ideas:
- Too Close to the Sun: Venus is much closer to the Sun than most other planets, and the Sun’s strong gravitational pull could destabilise the orbit of any potential moon. This might cause a moon to either crash into Venus or be flung out into space.
- Moons Are Rare in the Inner Solar System: None of the inner planets (Mercury, Venus, Earth, Mars) have many moons. Earth has just one, and Mars only has two tiny moons. Most moons are found around the outer planets, like Jupiter and Saturn, which each have dozens of the things. Perhaps the Sun's gravitational influence makes it harder for moons to form or remain stable in the inner Solar System.
- Venus Just Got Unlucky: There might not actually be a specific reason preventing Venus from having a moon. It could be that a moon could exist around Venus, but the right conditions for it to get one just never occurred. After all, if the giant collision that gave Earth its moon hadn't happened, Earth might be moonless as well.
- Venus did have a moon, but lost it: Now that’s an interesting idea – so interesting that it deserves its own section.
It’s possible that Venus had a moon long ago. In 2006, scientists from Caltech suggested that Venus may have had a moon billions of years ago, formed by a large collision similar to how Earth’s moon was created. However, a second massive collision could have reversed Venus' rotation and caused its moon to eventually crash back into the planet.
This theory could explain Venus' retrograde rotation (it spins clockwise, unlike most planets) and its extremely slow rotation speed. While most planets rotate in hours - Earth takes 24 hours, Jupiter takes 10 hours for example - Venus takes 243 Earth days to complete a single rotation!
In the 17th Century, some astronomers, including Italian astronomer Giovanni Cassini, reported seeing a mysterious object near Venus, which they named Neith. However, modern observations have shown that it was likely a star or an optical illusion.
If they ever do find a moon around Venus, I think they should called it Keith. That would be funny.
Moons are referred to as natural satellites. The word "satellite" refers to any object that orbits another object, and a natural satellite means it wasn’t made by humans. Artificial satellites are human-made and are sent into space to orbit planets or other objects.
