Did Planet Earth Once Have Two Moons?
Astronomers from the University of California, Santa Cruz have uncovered evidence suggesting that two moons once orbited Earth.
They speculate that the second moon -- which was about 1/3 the size of our current moon -- was formed in the same collision between Earth and a Mars-sized object that scientists believe created our existing moon. Then, after orbiting earth for tens of millions of years, this second moon smashed into the larger moon and the two moons became one, as illustrated in the above graphic.
The imprint of this massive-space collision would also explain the stark differences in topography between the two sides of our moon.
That said, we've got nothing on some other planets: Jupiter still boasts a whopping 64 moons today.