How Many Moons Does Earth Have?

The Earth is unique among the inner planets of our solar system for many reasons, one of which is the presence of a large moon. While Mercury and Venus do not have moons, and Mars has two tiny moons, the Earth’s moon stands out among the worlds of the inner solar system. However, is the moon the only moon that Earth has? While the general consensus is that Earth only has one moon, there is the occasional object that falls into Earth orbit that could be defined as a natural satellite.

What is a Moon?

The moon
A moon is a celestial body that orbits a planet.

In order to understand whether or not the Earth has more than one moon, we must first know what a moon is. A moon is simply defined as a celestial object that orbits a planet. Interestingly, there is no defined size limit for how big or how small a moon has to be. So long as it's a celestial, natural occurring object that orbits a planet, it is defined as a moon.

Is the Earth Orbited by More Than One Moon?

Asteroid and Earth
Occasionally, an asteroid may fall into Earth orbit and become a small, temporary moon.

While the moon is the largest object that orbits Earth, there are several other known objects that orbit our world from time to time. Most of these objects are near-Earth asteroids and meteors that orbit the sun in reconnaissance with the Earth, hence they appear to orbit the Earth. Some asteroids occasionally fall into Earth’s orbit for a short period of time and become temporary moons. While the moon is the only large, permanent satellite of our world, we do get the occasional mini, temporary moon. 

Did the Earth Have More Moons in the Past?

Planets colliding
Image depicting the collision between Earth and another planet.

Some models of the moon’s formation suggest that the Earth may have had two large moons in the distant past. The moon formed around 4.5-billion years ago after the young Earth underwent a collision with a Mars-sized planet. While the solar system is home to eight planets today, as many as a hundred planets coalesced from the solar nebula. Astronomers believe that every planet in our solar system, including the Earth, underwent one or more collisions with the other forming planets. Around 4.5-billion years ago, the Earth collided with another planet. The impact resulted in a tremendous amount of debris that fell into orbit around the forming Earth. That debris went on to form the moon, yet some models suggest that it may have actually formed two moons that eventually collided to form Earth’s current moon.