A new theory suggests Earth may have stolen Venus' moon.
The idea challenges the widely accepted theory that the moon was formed when an unknown planet made impact with Earth at high speeds 4.5 billion years ago, Space.com reported.
"I think part of the key to [understanding] the moon may be that Venus has no moon, and we certainly have to study [Venus] more," Dave Stevenson, professor of planetary science at the California Institute of Technology who presented the idea at a Royal Society conference, told Space.com.
The theory suggests the Earth used its gravity to reel in Venus' moon and then adopted it as a satellite. The problem with this idea is that moon rocks brought back from lunar missions prove to have a similar isotopic composition to Earth.
Alex Halliday, head of science at Oxford University said the isotopic similarities suggest "the material that makes up the moon did actually either come out of the Earth, or that the stuff that was in the disk that formed the moon got completely mixed up with the stuff in the Earth."
Despite the technical issues, Halliday does think the idea is an interesting take on the moon's formation.
"The reason why it's interesting is that Earth and Venus are close to each other. They have similar mass, and people think they have probably formed in a similar way. So the question is, if Earth and Venus formed in similar ways, how come the Earth has a moon and Venus doesn't?" He said, Space.com reported.
There is still hope for the "moon capture" theory. If scientists are able to find similarities in Venus rock isotopes than it would work in favor of the idea.
"We cannot understand the terrestrial planets unless we understand Venus, and at the moment, we don't know anything about Venus in terms of the isotopes" it has, Stevenson said. "And I also think that as a test of our understanding of the origin of the moon, we need to understand whether Venus ever had a moon."
Another theory on the moon's birth is that it "'fissioned' from the Earth's crust and mantle due to the centrifugal force of a rapidly spinning early Earth," Space.com reported. Other people believe the moon was simply born at the same time as Earth.
