Earth Stole Its Moon From Venus, Caltech Professor Suggests At 'Origin Of The Moon' Conference
A professor of planetary science from the California Institute of Technology has accused Earth of stealing its moon from Venus. Caltech professor Dave Stevenson told the Origin of the Moon conference in London that it's an "interesting possibility" to consider that Earth, which has one moon (obviously), may have swiped Venus's moon, a planet that has no moon at all.
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Stevenson's theory puts forth the idea that Earth's gravity was able to pull Venus's moon away. Earth and Venus are close to one another, have similar mass and are believed to have been formed in the same way, all of which makes Stevenson think a moon swipe would have been possible. There are enough holes in the prevailing theory for the moon's origin, Stevenson says, that ideas like moon theft are worth exploring.
The prevailing theory for the moon's origin is known as the "giant impact," which states that the Moon formed from the resulting debris of a collision between Earth and another body. That event is believed to have happened 4.56 billion years ago, or perhaps a little earlier, according to a recent Origin of the Moon speaker who put it at between 4.4 billion and 4.45 billion years ago. There's a wealth of supporting information behind the giant impact hypothesis: lunar and terrestrial rocks have identical isotopes and probably have a common origin; the spin of Earth and the orbit of the moon have similar orientations; and big collisions like the theorized giant impact are consistent with how we believe the solar system formed.
But we don't know enough about Venus to know whether their rocks are similar to those found on the Earth and moon, says Stevenson. Most of what we know about Venus comes from radar observations; no probe has been able to survive on the Venus surface for over an hour, due to the planet's high heat and pressure. So it's possible that Venus and the moon share isotope similarities in the way that the Earth and moon do.
"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 [planet's] isotopes," said Stevenson. "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."
Sean Solomon, the director of the Lamont-Doherty Earth Observatory of Columbia University, told Space.com that there are enough questions about the giant impact theory that other theories could still hold water.
"We are still on the trail of the detailed scenario that would seem both likely and complete in its ability to account for all the geochemical and geophysical observations," Solomon said. "Even with the giant impact idea, we don't know the origin of the impacting object. It could've been an early protoplanet. It could've been a moon of another object that was removed from the gravitational field of its original [planet]. It could've been a very large asteroid. All of those scenarios are still open."
Including the scenario in which Earth is a lowdown moon thief.
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