Why Does Earth Have Only One Moon, Whereas Other Planets Have Hundreds?

At night, you may see the moon shining brightly from hundreds of millions of miles away. However, if you visited Venus, this would not be the case. Why do certain planets have multiple moons while others have none?

First, a moon is known as a natural satellite. Astronomers define satellites as objects in space that orbit larger things. A moon is classified as a natural satellite because it was not created by humans.

Currently, there are two basic ideas about why some planets have moons. Moons are either gravitationally trapped or created as part of a solar system. Objects attract other adjacent objects by their gravitational force. The force of attraction increases with the size of the object.

This gravitational force keeps us all tethered to Earth rather than floating away. The solar system is controlled by the sun’s massive gravitational force, which keeps all of the planets in orbit.

The Sun is the largest massive object in our solar system; hence, it has the greatest gravitational pull on objects like planets. To orbit a planet, a satellite must be close enough for the planet’s gravity to keep it in orbit. The Hill sphere radius is the minimal distance required by a planet to keep a satellite in orbit.

The Hill sphere radius is calculated using the masses of both the larger and smaller objects. The moon orbiting Earth is an excellent example of how the Hill sphere radius works.  The Earth orbits the Sun, but the Moon is close enough to the Earth to be captured by its gravitational pull.

Because it is within the hill sphere radius of Earth, the moon revolves around it rather than the sun. Mars has two moons: Phobos and Deimos. Jupiter, Saturn, Uranus, and Neptune have bigger hill sphere radii than Earth, Mars, Mercury, and Venus because of their larger sizes and distance from the Sun.

Another theory suggests that some moons formed at the same time as their solar system. Finally, the reason why some planets have moons is still contested, but elements such as a planet’s size, gravitational pull, Hill sphere radius, and how its solar system developed may all play a part.