New Take On an Ancient Mystery: How Earth Got its Moon

Lunar history has always been murky, and a new paper offers additional riddles

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Correction appended Dec. 4, 2013

It’s a general rule in science that the more you know about some aspect of the natural world, the better you understand it. But rules are sometimes broken, and the question of how Earth got its Moon is a very good example of that. Planetary scientists back in the early 1980s concluded that the Moon was born around 4.5 billion years ago, when a Mars-sized object, now deceased, struck Earth a glancing blow at a relatively slow speed, creating a disk of debris that congealed into the familiar, modern Moon. That scenario fit nicely with Earth’s rotation rate and the Moon’s orbit and made particular sense since 4.5 billion years ago, there was a lot more free-flying debris in the solar system than there is today. Plus, says Sarah Stewart, a planetary scientist at Harvard, “It’s something you could explain in a sentence to your grandmother.”

Unfortunately, a growing body of evidence suggests that what we’ve been telling grandma is probably wrong—and a report just published in Nature makes clear exactly how murky the story of the Moon’s origin has now become. The central problem with the original theory, says author Robin Canup, of the Southwest Research Institute in Boulder, Colorado, is geological: the Moon simply looks too much like the Earth. “The disk of debris that formed the Moon should have come mostly from the impacting body,” she says, “which we think should have had a chemically different composition from Earth.”

Geologists have known for a long time how closely moon rocks resemble Earth rocks—ever since the Apollo astronauts began bringing back lunar samples and NASA labs had a go at them. The first clue was the fact that isotopes (or chemical variants) of oxygen locked in lunar material and terrestrial material were identical. But that finding was  swept aside as mere coincidence. As analytical techniques got better, however, Stewart says, “the geochemists got more and more antsy,” because more and more isotopes—of tungsten, titanium, chromium, silicon—were coming in looking identical as well. “We could have bought one match,” she says, “but not all of these.”

(MORE: China’s First Moon Rover Blasts Off)

One way around the problem: assume that somehow that long-ago impact vaporized not just part of the Mars-size intruder, but significant parts of Earth’s upper layers as well. If all of that material got blended together, with some of it congealing into the Moon and the rest falling back to Earth, you wouldn’t be surprised that the surface of both Earth and Moon look geologically similar. Unfortunately, that doesn’t work: it would take 100 years for Earth and impactor debris to mix thoroughly, and in the deep freeze of space, the Moon would have started to congeal more quickly than that. Heavier elements like tungsten, moreover, would condense too quickly for the contributions of Earth and impactor ever to reach chemical equilibrium with each other.

Another fix to the theory involves ramping up the speed of the impact, or assuming that Earth was significantly smaller at the time and that the impacting body was bigger than Mars. That would have made the collision much more violent and accelerated the rate at which the debris from both bodies melted and mixed. But there’s a problem here too: based on the Earth’s current rotation rate and the moon’s orbital distance, the Earth had to be rotating about once every 5 hours just after the impact (it slowed gradually to 24 hours, and the Moon retreated to its current distance, through tidal interactions between the two bodies).

The old theory was consistent with this post-collision rotation rate. Speeding up the impact would make Earth rotate more like once every two hours after the crash. That’s too fast to explain today’s 24-hr. day—unless you invoke some extra factor, like a previous collision that slowed Earth’s rotation before the Moon-making collision sped it up again, or a tidal interaction between Earth, moon and Sun that slowed Earth down after the collision.

(MORE: Hands off Our Lunar Landing Sites? Not So Fast)

Either is possible, but, says Canup, “Every time you add an extra complication, you reduce the overall probability of an event happening. Maybe we’re just missing something. There could be a scenario we haven’t thought of.”

It’s also possible that the key problem with the original theory isn’t a problem after all. Planetary scientists assume the Mars-size impactor they first cooked up in the 1980’s would have been geochemically different from Earth because Mars itself is different—something we know from the chunks of Mars that have made their way to Earth.

(MORE: Space Nuts Are in a Bidding War Over Buzz Aldrin’s Underwear)

But maybe that difference is a fluke. Maybe Venus, which is nearly identical to Earth in size, is nearly identical to Earth geochemically as well—something we can’t know without a sample return mission, since meteorites from Venus have never been found. If Venus and Earth are indeed made of the same stuff, that would raise the odds that the impactor was too and the collision theory would once again make sense.

“If the composition of Venus turned out to be very similar to both the Earth and the Moon, that would change everything,” says Canup. And by change everything, Canup means keeping everything more or less the same, with the old model—which explains so much so elegantly—back in place. Not for nothing, it would also restore the scientific rule of thumb that the more you know, the more you actually understand.

(VIDEO: How Greenhouse Gasses Saved Mars)

Correction: The original version of this story misspelled Sarah Stewart’s name. It is Stewart, not Steward.

20 comments
Aphugel
Aphugel

To all those lovely xtian trolls posting here.
The problem is not that you are stupid beyond measure. The problem is that you are too stupid to understand how stupid you are, and that there is no earthly way to convey it to you.
You do NOT have the right to an opinion in these matters, just like a kid riding on the shortbus does not have the right to discuss (in a loud voice...) why in his opinion two and two should equal five.
You have only the right to remain silent and to retreat into your fairy tale world of illogic and stupidity.
Now please. On the double.

JohnStell
JohnStell

congeal.  so the idea is that giant rocks from a massive, catastrophic collision magically 'congeal' in space to form a nearly perfectly spherical object.  Extreme order and beauty from chaotic catastophe.  Really?  And that has just been accepted for 3 decades as truth? 

Lunar recession is also a problem for origin of the moon hypotheses.  And remember when the put wide landing feet on the Apollo to help it from sinking into the meters of dust.  Oops.  I like how the planets and their moons vary widely in their rotation and tilt.  It doesn't fit the standard hypotheses.

Problem is, these problem aren't allowed to be discussed in schools.  Almost all Creationists and ID proponents are not asking to teach any of their science with all it's supporting evidence.  They merely want freedom of information so children can understand the problems and shortcomings or Darwinism, materialism and age of the universe.  but they are labeled as 'flat earthers', much like global warming 'deniers', and attacked as dangerous.  So much for freedom.  Atheistic scientists should be begging creationists to come in and present their evidence - it should be so easy to disprove them and refute what so many parents and 'non-experts' still teach.

lisacoc
lisacoc

Either is possible, but, says Canup, “Every time you add an extra complication, you reduce the overall probability of an event happening. Maybe we’re just missing something. There could be a scenario we haven’t thought of.”

Read more: Where Did the Moon Come From? New Clues | TIME.com http://science.time.com/2013/12/04/new-take-on-an-ancient-mystery-how-earth-got-its-moon/#ixzz2mcbtkJ8r

Uhhhh??? Ya' think? Give God the credit! Like JenniferYoung1 said - read the Bible - Genesis Chapter 1! Billions of years ago - pffft.

JenniferYoung1
JenniferYoung1

Genesis 1:14-18

Then God said, "Let there be lights in the expanse of the heavens to separate the day from the night, and let them be for signs and for seasons and for days and years; and let them be for lights in the expanse of the heavens to give light on the earth"; and it was so.  God made the two great lights, the greater light to govern the day, and the lesser light to govern the night; He made the stars also.  God placed them in the expanse of the heavens to give light on the earth, and to govern the day and the night, and to separate the light from the darkness; and God saw that it was good.

Godscreation
Godscreation

Allah created Moon as he created earth and the whole universe

3dot14159265358
3dot14159265358

The moon was a planet formed with the same material in an orbit close to the Earth's. One day a wondering star visited the solar system...it can only happen once or twice in a billion years...& disturbed their orbits, pushing the Moon into the Earth's arms. Since then the Earth has had its faithful companion. 

MillerTXUS
MillerTXUS

Referring to the quote, "" Either is possible, but, says Canup, “Every time you add an extra complication, you reduce the overall probability of an event happening. Maybe we’re just missing something. There could be a scenario we haven’t thought of.” "" ... it is not something you haven't thought of, rather something that has been ignored.  Science is about a testable experiment that reproduces (or not) a hypothesis.  The probabilities here are based upon assumptions that are not scientific, rather religious since there is no testable basis for the assumptions... they are a belief.  This leads me to the point that it's not something that hasn't been thought of, rather, the blindness of the biblical explanations that have been well supported through historical and scientific research.  It's God's doing, not a random act of time.

bawgs
bawgs

@JohnStell They don't magically 'congeal' in space. It's called accretion. Astronaut Don Pettit, while in space, put salt in a plastic bag and shook it up and discovered that the granules stuck together. He accidentally discovered the beginning process of planet formation.

Hughmanhorn
Hughmanhorn

@JohnStell Oh my. How do sleep at night knowing you sat at a computer? Surely a computer is some form of witchcraft. Gravity is going to pull everything towards the center of it's mass. Did you sleep through school? As for the congeal part you don't have to go far to see evidence of melted rock, we're standing on one. Go to northern Ontario to see what rock looks like under the weight of what used to be the largest mountains on the planet. (Hint they look like they flowed) Not that it matters to you because those rocks can't be that old and appeared from thin air to look like that. Or maybe the mountain vanished. God must be the ultimate prankster since he loves hiding mountains and burying fossils of animals that never existed.

Hughmanhorn
Hughmanhorn

@lisacoc The article is not taking credit from God, but you sure are as a representative of God "pffft'ing" what you think you know about the history of the universe and what a creator may or may not have done. I bet if this creator exists it never intended for people to speak on it's behalf. Lets worry more about things like food, air and community (which science and technology help with, seeing we are spreading like wild fire) and not whether something is "discovered by science" or "can't be discovered because God made it".

bawgs
bawgs

@JenniferYoung1 Perhaps you didn't notice this was in the "SCIENCE and space" section of Time.com. This is not the "Made Up Nonsense" section. Post this crap somewhere else. Also, I love how just because highly educated scientists can't fully explain something, some religious nutjob just says GOD and we're all supposed to believe that solves anything. 

ZacPetit
ZacPetit

@3dot14159265358 You'd have to prove the physics with a simulation (extremely unlikely) and then account for how two distinct heavenly bodies were created "with the same material."

JohnStell
JohnStell

I see you are open minded, and familiar with the plethora of other problems with Darwinism and age of the universe.  You have clearly advanced beyond the rest of your kind via Evolution.  

I recognized the common traits you share with your well evolved kin - ad hominem attacks, name-calling, bullying, rudeness, miscongeniality, hubris, typing in all CAPS, hypocrisy (accusing of God of the gaps while invoking Darwin of the Gaps), supression of discussion, reason, and freedom, et al.  Thank GOD for DARWINISTS - the FUTURE of our SPECIES is in the hands of those with no basis for MORALITY!  We can look forward to more of this treatment for those who dare move out of lockstep.

OmBlackmatter
OmBlackmatter

@bawgs @JenniferYoung1 you might not agree with jen but its actually true... 

if you knew more on and from the bible you would understand that science and the bible (at least the hebrew one)  have almost everything that we know correct and identical including the time of the universe

so please take a deep breath and learn.. i mean for real, learn!

bawgs
bawgs

@JohnStell And John, I like how you just did everything you just accused me of. Name calling, typing in all caps, hypocrisy... There is no place for God in a scientific discussion. You are free to believe whatever you want but that doesn't mean it should be accepted as scientific fact, or even theory. Like I mentioned to one of your fellow delusionists, even if there were a God, it doesn't mean that there's not a scientific explanation for why the moon is there. And what exactly is your connection to the fact that I don't believe in God therefore I must be a immoral person? I guess you must also share traits with your less evolved kin. And for the record, I never stated that Darwinism is absolute truth, that's why it's called the THEORY of evolution...you see that's how science works, if it can't be proven, it's only a theory. Unlike religion however, we need more than one source to explain the many mysteries of life.

DanielMenard
DanielMenard

And they call us Christians bigots.  Interesting.  I normally dont bad mouth other peoples beliefs.  I let them believe what they want and when they are ready for the truth then I will answer them.

ReyJesusito
ReyJesusito

@Hughmanhorn @bawgs @OmBlackmatter @JenniferYoung1  just take a look at this please
Job 26:7
He spreads out the northern skies over empty space; he suspends the earth over nothing.
You may be surprised to learn that the Bible revealed that the earth is round.  
Isaiah 40:22, 
It is he that sitteth upon the circle of the earth, and the inhabitants thereof are as grasshoppers; that stretcheth out the heavens as a curtain, and spreadeth them out as a tent to dwell in:

Hughmanhorn
Hughmanhorn

@bawgs @OmBlackmatter @JenniferYoung1 Sorry to break it to you bawgs, but we're still waiting for physicists to prove how cheek turning works. Until then we'll have religious people trolling science articles. Surely there is a story about "Live and let live" in the Hebrew bible or maybe those pages never survived.

bawgs
bawgs

@OmBlackmatter @bawgs @JenniferYoung1 Look, if you want to believe in fairy tales, go right ahead, but even if I pretend that God is real, it doesn't mean that science doesn't exist. There is a scientific explanation for where the moon originated and it has nothing to do with your spaghetti monster. You, of all people, should take your own advice and go out and learn something that can actually be proven by facts, not "faith".