Since a suite of spacecraft confirmed abundant water on the moon in the past few years, scientists have wondered how it got there. Could it have come from comets, dusty snowballs making their way toward the sun and melting? Could it have come from meteorites, collecting tiny amounts of water over time? Or maybe even the sun, donating hydrogen particles from its blustery wind that combined with lunar oxygen? Now there's a new theory: It came from Earth.
Most moon-formation theories hold that the moon came from the Earth, and was sheared off when a Mars-sized object walloped our planet in its youth. And just a couple months ago, scientists reported that the moon probably has had water its entire life. A new study that examines lunar water evidence could explain this: Earth had water when this happened, and that somehow, it survived the collision and wound up on the moon.
Alberto Saal, associate professor of Geological Sciences at Brown University, and colleagues examined some Apollo moon rocks, specifically looking for a phenomenon called melt inclusions. These are small pockets of volcanic glass, usually trapped inside a mineral called olivine.
Previous research by a co-author on this paper, Erik Hauri, showed that these melt inclusions have water in them--a lot of it, too, as much as lavas forming on Earth's ocean floor. Saal et al. set out to find where that water came from.
They examined rocks from Apollo 15 and 17 and found the hydrogen isotope ratios were the same as water on Earth. Deuterium, a heavy form of hydrogen, is found in about three-tenths of a percent of Earth water. This ratio is indistinguishable from that of carbonaceous chondrites, the most common and oldest type of space rock in these parts. But it is very different from the ratio found in most comets.
Scientists think meteorites may have delivered Earth's water a long, long time ago, when the solar system was just 100 million years old--but they thought comets may have delivered it to the moon.
If the ratios are the same, that could mean the water on the moon is the same as the original water on the Earth, and that could mean Earth was already watery when something huge bombarded it and formed the moon. That also means somehow, the water didn't vaporize in the unspeakable cataclysm that took off a giant chunk of our planet. That would be very strange, and that question needs further probing.
Or, it could mean the Earth and the moon were bombarded by the exact same family of meteorites shortly after they separated from each other.
"The new data provide the best evidence yet that the carbon-bearing chondrites were a common source for the volatiles in the Earth and moon, and perhaps the entire inner solar system," Hauri said in a statement.
The results were published online today in Science Express.
If the moon was a big chunk of the earth, why wouldn't we see some kind of evidence to support the theory? I.E. an odd shaped earth or something. I understand the earth is not perfectly round, but that's a pretty large chunk. I would also expect the moon to be something other than round. Plus, there'd be a good chance we would have had multiple moons instead of just the one.
I think the moon is round because when it broke off, the big proto-Earth (and by extension, the moon) were very hot, and thus gravity acting on these large materials was still able to shape them into somewhat circular objects.
Don't quote me though, but that's my guess.
That makes sense. You'd have to think that if the earth was molten then what ever hit the earth would have been molten too. (I would assume)Then that would mean finding signs of water on any planet is possible.
It's all speculation and beyond the scope of science.
I have heard the theory about the moon coming from earth before but what I am wondering is if the Earth got hit by something about as big as Mars to make this happen then how did Earth not get thrown out of orbit?
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I am just guessing here. If the Earth was hit by an object as large as Mars and this was in the early days when Earth and many other objects in the solar system was mostly hot and soft, one object speed energy would exchange to another’s objects and if the Earth loss or gain mass these things could change its orbit around the sun. To what extent, are all theories, since the smarty’s with the best ideas were not there.
And while all the debris of the explode rock fragments came from Earth, orbited Earth eventually came together form the moon. The moon as it became solid orbits the Earth is slowly leaving Earth and if nothing else changes over time will eventually leave Earth and head out to the cosmos.
Once upon a time as the moon formed, it seems it would reach a balance state, fixed in orbit around the Earth. Why will the moon eventually leave the Earth? It would have gained more speed after forming it a final mass, but how?
I suppose we are lucky as the moon formed that gravity just didn't pull it down and crash it into the Earth, too.
HandThumb there's this thing called gravity that's how most planets and moons get their shape. So if a big chunk of the earth got knocked off it goes flying off and gravity basically compresses it into a big ball.