The Earth once boasted two moons, according to Professor Erik Asphaug from the University of California at Santa Cruz. The smaller moon is believed to have lived for a few million years before it collided with our current moon in a dramatic event.
Asphaug plans to detail the theory at a conference about the moon, which will be held at the Royal Society in September. However, he explained some of the twin moon theory, saying:
"The second moon would have lasted for only a few million years; then it would have collided with the moon to leave the one large body we see today."
He went on to explain that the Earth's second moon orbited at the same speed and distance as its much larger twin. But then it "just got slowly sucked in until they hit and then coalesced."
The moon as we see it today appears to have mountains on its landscape. Professor Asphaug explained that he believes these mountains are the remains of the second moon. The former celestial body is believed to have been one-thirtieth of the size of our current moon.
There are several theories about the moon and the Earth, including one published last year by scientists from Harvard. They suggested the moon was once part of Earth, but it spun off after the planet collided with another body. And Asphaug isn't the first to suggest the Earth once had two moons.
This isn't the first time that Ausphaug has suggested the Earth once had twin moons. He argued the point previously in 2011 when his work was published in the journal Nature. He collaborated with colleague Martin Jutzi of the University of Bern in Switzerland to present the theory.
The theory is based off the very different topography of the far side of the moon, which was first photographed in 1959 by the Soviet Luna 3. The moon's near side is comprised of widespread plains of volcanic rock. However, the far side only has a few. The surface of the near side is also mostly low and flat. The far side is high and mountainous.