The planet Earth's moon may have been a gift from Venus, according to a professor at the California Institute of Technology. The planet Venus once had a moon but lost it, presumably to Earth, Yahoo! News reports.

The theory posited by Dave Stevenson, professor of planetary science at the California Institute of Technology, suggests that the moon in Venus had been pulled towards Earth because of gravity, and that the Earth's natural satellite is actually not its own.

Previous theories held that the Earth's moon was formed around 4.5 billion years ago due to a high-speed collision between the planet and another celestial body. This giant impact theory has its flaws, pushing scientists to continue studying the origin of the Earth's moon, Mother Nature Network noted.

Stevenson's theory however, met little support compared to the previous theory, as lunar experts acknowledge the fact that the giant impact theory has more merit since the Earth and the moon have isotopic similarities; and it's more likely possible that the Earth has essentially 'given birth' to the natural satellite, reports UPI.com.

Stevenson himself admitted that he found the giant impact theory more plausible, but he quickly added that the idea contained so many glitches, it was time to look elsewhere. He said, "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?" noted Mother Nature Network.

This new theory is just one among the many other ideas that scientists presented at the Royal Society conference in London. For now, the moon origin concept continues to be open for determination.

The planets Venus and Mercury have no moon, while Earth only has one, and the planet Mars has two. Jupiter, an outer planet, has 67.