A city in China wants to launch an artificial moon into orbit by 2020 as a way to reduce energy needs by replacing street light with artificial moonlight. Regardless of whether or not they succeed, their ambitious idea really made us wonder…
What would happen if Earth had two moons?
Well, it wouldn’t be pretty.
Imagine the Moon’s identical twin comes hurtling by and is trapped by Earth’s gravity. As it settles into orbit, halfway between Earth and our original moon, it yanks violently at the oceans. In the real world, this is how our original Moon helps generate tides. So, the second moon would amplify the effect. Causing peak tides that would be 6 times higher, eroding shorelines and flooding many of our world’s greatest cities including: New York, Singapore, and London — gone.
But not all destruction would happen on Earth. The combined pull of the planet and the original moon would also yank on the second moon. The second moon would be caught in a tug of war between Earth and the original moon. The gravitational pull back and forth from both ends would warp the second moon’s surface triggering tremendous volcanic activity. Flooding the second moon’s surface with red-hot rivers of lava. Just like hundreds of the volcanoes you see today on Jupiter’s hellish moon, Io.
But even that’s not the end of the spectacle. Right now, our current moon is spiraling away from Earth at 3.8 cm a year. That’s about how fast your fingernails grow. At the same time, it pulls on the Earth slowing down the planet’s rotation. Which is actually lengthening our days by around 1 second every 40,000 years. It may not sound like much, but with two moons in place it would accelerate this process even more.