Unlike many other planets in the solar system, Earth only has one natural satellite, universally called the ‘Moon.’ But have you ever stopped to think about what might happen if Earth had two moons? The result probably wouldn’t be as peaceful as what we see on Tatooine in the popular science fiction Star Wars.
If a second object as large as the moon suddenly found itself within Earth’s orbit in between Earth and the existing Moon, the gravitational influence would impose significant changes to the world as we know it. Oceanic tides would rise by as much as six times, swallowing major cities like New York, Singapore, and London. In addition to rising tides, the Earth’s rotation would slow over time.
These gravitational forces would likely also impact the new moon itself. Stuck in a gravitational tug of war between the Earth and the Moon, the newfangled moon would elongate over time, triggering intense volcanic activity on the body as we see on Jupiter’s moon Io.
But most frightening of all is the reality that the two moons could potentially collide with one another, sending debris flying in all directions, including toward Earth. Some of the larger fragments would leave devastating impact craters on our planet, and those that didn’t strike Earth would gather around the equator to form a planetary ring that would slowly clump back together into a single moon.
As dull as it sounds, it's probably a good thing that Earth only sports one Moon.