Lunar Ballistics Sheds More Light on Cataclysmic Origin of the Moon

Lunar Ballistics Sheds More Light on Cataclysmic Origin of the Moon

The long-standing theory on our moon's origin gains a heap of evidence - and a small twist - thanks to a study out of UCLA.

For an object that has inspired myth, poetry, and general reverence the way it has for all our history, the moon's origin is a little bit more Michael Bay than, say, Sylvia Plath. The consensus is that our favorite satellite was ripped from the Earth's own still-forming crust more than four billion years ago, after a devastating collision with another planetoid.

That consensus has been shaken up, somewhat, by a recent study out of the University of California in Los Angeles. Whereas scientists have once believed the initial crash was more like a side-swipe, the truth is more violent, and direct.

About four and a half billion years ago, the embryonic planet we now call "Theia" was simply minding its own business, circling our sun in an orbit that overlapped Earth's. Theia, named for the Greek titan who gave birth to the moon, may have been the same size as Earth or slightly smaller. It smashed head-on into its sister planet, sending fragments into orbit that would coalesce into the moon.

In the gallery below, you can see a close-up of the lunar rock, as well as paintings by scientist William K. Hartmann depicting the current theory (which looks like two planets undergoing mitosis) and the previously held one.

This new theory comes about after the chemical makeup of lunar rocks and the Earth's crust was compared by scientists at UCLA. They were looking at oxygen isotopes - each planet in the solar system has its own ratio of oxygen-18 isotopes to oxygen-19. Earth's is about 99.9% oxygen-18, and so is the moon's.

"We don't see any difference between the Earth's and the moon's oxygen isotopes; they're indistinguishable," says Edward Young, lead author of the study.

If the cataclysm that birthed the moon was a glancing blow, as we used to think, we would expect those ratios to be very different.

"Theia was thoroughly mixed into both the Earth and the moon, and evenly dispersed between them," says Young. "This explains why we don't see a different signature of Theia in the moon versus the Earth."

That's a nice way to end this story, really. Theia, the planet, was destroyed; yet there remains some Theia in all of us. Maybe some Plath is still appropriate: something beautiful, but annihilating, indeed.

Source: Forbes, UCLA

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When I read the title; "Lunar Ballistics", I assumed that our war against the moon and it's cheese hording inhabitants, the Lunarians, had finally kicked off in to high gear. But I suppose learning how the Moon was formed is kinda cool too.

The straight-up violence involved in stellar and planetary formation is straight up awesome. As in the older meaning of the word: it causes awe, and not a little bit of fear.

Cheers, Escapist, for my daily dose of proving just how small a fragment of a sliver of a fraction I am in this universe! :D

And anaxagoras was right.
Too bad he was an antique filthy pagan, and not a god-favorite miraculous-maker divinely-created chosen one.

Anyway, what's really interesting here is we were "close" to have a sister earth on the same orbit.
Would it be fascinating to imagine two rock planet sin the same habitable zone, but each on the opposite side of the same orbit? Two earthiankinds evolving simultaneously on each own planet ... and then meeting at the space age.
A good pitch for any fiction.

mtarzaim02:
And anaxagoras was right.
Too bad he was an antique filthy pagan, and not a god-favorite miraculous-maker divinely-created chosen one.

Anyway, what's really interesting here is we were "close" to have a sister earth on the same orbit.
Would it be fascinating to imagine two rock planet sin the same habitable zone, but each on the opposite side of the same orbit? Two earthiankinds evolving simultaneously on each own planet ... and then meeting at the space age.
A good pitch for any fiction.

I've seen that plot a few times. Go watch Spider-Man Unlimited.

mtarzaim02:
Anyway, what's really interesting here is we were "close" to have a sister earth on the same orbit.
Would it be fascinating to imagine two rock planet sin the same habitable zone, but each on the opposite side of the same orbit? Two earthiankinds evolving simultaneously on each own planet ... and then meeting at the space age.
A good pitch for any fiction.

Not possible, I'm afraid, the orbit isn't stable in the long term. And if one was orbiting ever so slightly faster or slower than the other, one would catch up to the other before life evolved.

Also, no reason why they've evolve at the same rate and develop spaceflight at the same time either. Could easily be a few hundred millions years earlier or later.

OTOH, perhaps two moons of the same gas giant could be life supporting. Be easier to travel from one to another than go interplanetary, which we've still not done.

mtarzaim02:
Anyway, what's really interesting here is we were "close" to have a sister earth on the same orbit.
Would it be fascinating to imagine two rock planet sin the same habitable zone, but each on the opposite side of the same orbit? Two earthiankinds evolving simultaneously on each own planet ... and then meeting at the space age.
A good pitch for any fiction.

Nah. No Theia impact no Moon, no Moon and Earth would be unable to sustain life as we know it. So no earthiankinds to evolve and meet up.

If there was another planet on the same orbit, where did it go? Would the impact have caused it to leave the orbit? And if so, wouldn't Earth have left the orbit as well?

Oh, it says it was destroyed. That seems convenient.

Glongpre:
If there was another planet on the same orbit, where did it go? Would the impact have caused it to leave the orbit? And if so, wouldn't Earth have left the orbit as well?

Oh, it says it was destroyed. That seems convenient.

It didn't "go" anywhere. It is part of the Earth and moon now.

Have you seriously never heard this idea before?

Wow. If this is how gods do childbirth, I'd hate to see what the sex is like.

Xeorm:
Wow. If this is how gods do childbirth, I'd hate to see what the sex is like.

Hotdog down a hallway? More like a hotdog down the grand canyon.

Gundam GP01:

Glongpre:
If there was another planet on the same orbit, where did it go? Would the impact have caused it to leave the orbit? And if so, wouldn't Earth have left the orbit as well?

Oh, it says it was destroyed. That seems convenient.

It didn't "go" anywhere. It is part of the Earth and moon now.

Have you seriously never heard this idea before?

I have may have heard it before, but I can't remember.

But it being apart of the earth doesn't really make sense to me. The OP says it was around the size of the earth. The earth wouldn't absorb it, and the moon would be a fraction of it, so where did the rest go? Plus the impact would impart so much kinetic energy, I can't see the earth maintaining it's orbit. Also, wouldn't a large chunk of the earth have been destroyed? But that could be explained by one of the oceans...

Glongpre:

Gundam GP01:

Glongpre:
If there was another planet on the same orbit, where did it go? Would the impact have caused it to leave the orbit? And if so, wouldn't Earth have left the orbit as well?

Oh, it says it was destroyed. That seems convenient.

It didn't "go" anywhere. It is part of the Earth and moon now.

Have you seriously never heard this idea before?

I have may have heard it before, but I can't remember.

But it being apart of the earth doesn't really make sense to me. The OP says it was around the size of the earth.

At the time, yes.

Glongpre:
The OP says it was around the size of the earth. The earth wouldn't absorb it, and the moon would be a fraction of it, so where did the rest go?

Well, let's take a look.

PatrickJS:

If the cataclysm that birthed the moon was a glancing blow, as we used to think, we would expect those ratios to be very different.

"Theia was thoroughly mixed into both the Earth and the moon, and evenly dispersed between them," says Young. "This explains why we don't see a different signature of Theia in the moon versus the Earth."

So both Theia and the Earth that it hit in the past were each about half the combined mass of both the moon and the Earth today. And when they collided, the mixed together and created the celestial bodies of the Earth and the moon as we know them today.

Glongpre:
Plus the impact would impart so much kinetic energy, I can't see the earth maintaining it's orbit.

I have a feeling that you're underestimating just how much inertia an entire planet has. Also, what makes you think that the orbit WAS maintained? Theia probably did change the primordial Earth's orbit, making it the orbit we have today.

Glongpre:
Also, wouldn't a large chunk of the earth have been destroyed?

From what I understand, basically the entire thing was completely fucked until both bodies eventually reformed as essentially a new planet.

Glongpre:
But that could be explained by one of the oceans...

Not in the slightest. Anything resembling our modern continents and oceans would not have existed when this would have happened.

Glongpre:

Gundam GP01:

Glongpre:
If there was another planet on the same orbit, where did it go? Would the impact have caused it to leave the orbit? And if so, wouldn't Earth have left the orbit as well?

Oh, it says it was destroyed. That seems convenient.

It didn't "go" anywhere. It is part of the Earth and moon now.

Have you seriously never heard this idea before?

I have may have heard it before, but I can't remember.

But it being apart of the earth doesn't really make sense to me. The OP says it was around the size of the earth. The earth wouldn't absorb it, and the moon would be a fraction of it, so where did the rest go? Plus the impact would impart so much kinetic energy, I can't see the earth maintaining it's orbit. Also, wouldn't a large chunk of the earth have been destroyed? But that could be explained by one of the oceans...

It was a similar size to the size the earth was at the time. Both planets were almost entirely destroyed, forming a huge molten mass containing the material from both planets. As it cooled, this eventually coalesced into the earth and the moon.

infohippie:
Both planets were almost entirely destroyed, forming a huge molten mass containing the material from both planets. As it cooled, this eventually coalesced into the earth and the moon.

Hmm ok, this makes more sense.

Gundam GP01:

Glongpre:
Plus the impact would impart so much kinetic energy, I can't see the earth maintaining it's orbit.

I have a feeling that you're underestimating just how much inertia an entire planet has. Also, what makes you think that the orbit WAS maintained? Theia probably did change the primordial Earth's orbit, making it the orbit we have today.

Glongpre:
Also, wouldn't a large chunk of the earth have been destroyed?

From what I understand, basically the entire thing was completely fucked until both bodies eventually reformed as essentially a new planet.

Glongpre:
But that could be explained by one of the oceans...

Not in the slightest. Anything resembling our modern continents and oceans would not have existed when this would have happened.

The planets becoming a molten egg settles most of my thoughts. Any debris lost would have been replaced by Theia.

And I am probably overestimating what a planetary collision would be like :P

So when Theia collided with Earth, and presumably the cores met, would this make some kind of cool looking semi imploding fireball?

 

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