How on Earth did the moon come into being? If you subscribe to the latest theory, the moon was born out of a nuclear explosion on Earth that sent a chunk of mass flying from the planet's core into orbit, where it finally became the moon. But cool as that sounds, some killjoy scientists are pooh-poohing the hypothesis, calling it "unnecessary," "nonsensical," and "not physically sensible." The standard theory of the moon's origin holds that a giant space object, possibly an asteroid, banged into Earth and sent a large piece of the planet flying into space. That piece eventually became the moon. But the composition of the moon doesn't seem to support this theory. Researchers say if an asteroid or some such object smashed away part of the Earth,
the Moon ought to be composed of about 80 percent of that object's constituent material and about 20 percent of the Earth's. But the makeup of moon rock closely mirrors that of the Earth [Popular Science].
An alternate theory,
known as the fission theory, suggests that the moon spun out of the rapidly spinning blob of molten rock that would later become Earth [Popular Science]. But no one has been able to explain what caused a huge chunk of earth to spin away and become the moon. Now, researchers
Rob de Meijer and Wim van Westrenem have proposed in an online paper that centrifugal forces may have concentrated heavy, radioactive elements like uranium and thorium at the boundary between the Earth's mantle and its core. Then, they propose,
a massive nuclear explosion occurred at the edge of Earth's core, flinging red-hot, liquid rock into space. The orbiting detritus gradually congealed into what is now our planet's lone satellite [Discovery News].
Such "georeactors" have existed on Earth before, albeit on a smaller scale than these researchers propose. But de Meijer and van Westrenem have gotten little support for their hypothesis, and plenty of scorn. Geophysicist Marvin Herndon, who has previously espoused the controversial idea that uranium once sunk to the earth's core and formed a georeactor there, isn't buying into the new theory. He says he's skeptical of a georeactor's existence at the earth's core-mantle boundary, explaining that
uranium is so heavy that when it liquefies in a nuclear reaction, it should fall to the Earth's core [New Scientist].
Other scientists asked how the researchers had modeled this kind of explosion, as Princeton University astrophysicist Richard Gott pointed out:
"How do they really know it would produce a thin jet of matter?" [New Scientist]
. Gott adds that if indeed the georeactor hypothesis was right, then Venus, which is similar in mass and composition to Earth, should have formed its own moon in a similar process--but it didn't. For further evidence, points out to Pluto, asking
"how do you explain Charon, the big icy moon of Pluto? That would require an 'ice-reactor', which is a nonsensical idea!"[New Scientist].
David Stevenson, a planetary physicist at Caltech, blew the whole theory right back into space, saying:
"The whole idea is not physically sensible," he says. "Life is too short to spend on things like this" [New Scientist
]. The researchers, however, aren't backing down. They say the best way to test this idea is to look for isotopic signatures on the Moon left over from when the "georeactor" exploded. If they're there, it's a good chance that Earth once went critical in a huge way, and our ghostly galleon was tossed into the heavens by the world's first nuclear detonation
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