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Study: Why the Moon's Far Side Looks So Different

Posted by samzenpus on from the good-side dept.

StartsWithABang writes 55 years ago, the Soviet probe Luna 3 imaged the side of the Moon that faces away from us for the first time. Surprisingly, there were only two very small maria (dark regions) and large amounts of mountainous terrain, in stark contrast to the side that faces us. This remained a mystery for a very long time, even after we developed the giant impact hypothesis to explain the origin of the Moon. But a new study finally appears to solve the mystery, crediting the heat generated on the near side from a hot, young Earth with creating the differences between the two hemispheres.

17 of 79 comments (clear)

  1. Cosmic Baking by djupedal · · Score: 3, Funny

    This is what happens when you don't read the directions on the package...

    1. Re:Cosmic Baking by Tablizer · · Score: 4, Funny

      But I like my buns crispy on top.

      uh, don't read too much into that.

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    2. Re:Cosmic Baking by sg_oneill · · Score: 2

      Good thing zits generally disappear once you leave your teenage years...you only get them later if you are really unlucky.

      Of course on geological/cosmic type time scales, by the time she leaves puberty, the main species on this earth will be homo-greyalien or something. We're not a species that seems like it wants to hang around too long, what with our whole "Lets invent nuclear weapons, venus out the atmosphere and then feed dolphins plastic bags" tendencies.

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  2. Rotation by SimonInOz · · Score: 4, Interesting

    The moon became tidally locked within a few million years after its formation (around 4.5 billion years ago), so it's been tidally locked for over 4 billion years.

    But really, did the earth stay hot enough for "a few million years" - hot enough to affect the locked side of the moon more than the other?

    The moon would have cooled somewhat faster, being smaller, but this theory requires the earth to stay hot enough to affect the "earth side" of the for a very long time after the moon has cooled enough to solidify.

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    1. Re:Rotation by Dan+East · · Score: 5, Interesting

      But really, did the earth stay hot enough for "a few million years" - hot enough to affect the locked side of the moon more than the other?

      The moon has no atmosphere, thus radiation from the earth cannot affect the far side of the moon at all. So obviously, even to this day, the earth still affects "the locked side of the moon more than the other". The question is simply how much. The moon and earth were both molten after the collision, so it was not a matter of the earth being hot enough to melt the moon, but merely the earth imparting energy to prolong the cooling of the near side. No matter what, the near side must have cooled slower than the far side - it's a straightforward matter of thermodynamics. One side of the moon was receiving energy from the earth while the other side was not. The near side didn't need to stay so hot it was incandescent, but merely "softer" so that small impacts would heal more on the near side than the far side, and the duration only needed to be long enough to result in some degree of visible difference, which is what we still see today.

      The whole thing sounds plausible to me.

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    2. Re:Rotation by sg_oneill · · Score: 3, Funny

      How does lunar recession affect things here?

      Space-ron-paul was right! Convert your lunar-coins to bitcoins before the collapse!

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    3. Re:Rotation by jfdavis668 · · Score: 4, Interesting

      At the time, the Moon did have an atmosphere. It was hot enough to vaporize silicon and aluminum, components of today's crust. What the paper is proposing is that the hot Earth keep the Moon hot enough to keep these elements vaporized on the Earth facing side, while the far side was cooler and the elements precipitated out. This would cause a migration of crustal components to the far side, thickening the crust. This way it was not as susceptible to puncture by falling objects.

  3. Re:Another medium.com story? by ColdWetDog · · Score: 2

    But this one has exclamation points!!!!!!

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  4. Re:Thought Gene Shoemaker figured this out... by mister_playboy · · Score: 4, Informative

    No, the article itself mentions the impact difference between the two sides should be less than 1%.

    The near side had much more surface in a liquid state during and after many of the impacts. The article claims heat from the Earth was the cause.

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  5. "Very Long Time?" by Guppy06 · · Score: 4, Interesting

    This remained a mystery for a very long time

    Martians notwithstanding, nobody had any idea what the far side of the moon looked like before 1959. Sure, 55 years may be "a very long time" for some people, but we're not exactly talking about something that puzzled Hipparchus here.

    1. Re:"Very Long Time?" by Charliemopps · · Score: 4, Insightful

      Unless you're a creationist. In which case the number is more like 6,000 years, which is still a pretty long time in my book.

      Even most creationists think the earth being 6k years old is nuts. Most think science is right for the most part and it just explains "how god did it" Keep in mind, the age of the earth is no-where in the bible. The 6k figure came from some idiots counting up begots and such... most of the christians I've talked to about the subject simply don't care and if God wanted them to make a big deal about the age of the earth they're pretty sure he'd have put a line there "and the Lord sayeth the world is 6000 years old and woe unto he who talkith about giant lizards"

    2. Re:"Very Long Time?" by techno-vampire · · Score: 2

      As I recall, people were very surprised to find out just how different the other side of the Moon is. Right up until the pictures came back everybody expected that both sides would be much more similar than they turned out to be.

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    3. Re:"Very Long Time?" by T.E.D. · · Score: 2

      Even most creationists think the earth being 6k years old is nuts. Most think science is right for the most part and it just explains "how god did it"

      Don't be nit-picky. When people say "creationists", they are generally using it as shorthand for Young Earth Creationists. Nobody says that out because it is too much of a mouthful, and if they said "YEC", few would know what they are talking about.

      If someone wants to talk about people who think science is right for the most part and it just explains "how god did it", they can just say "most Christians".

  6. Re:Thought Gene Shoemaker figured this out... by __aanbvm4272 · · Score: 2

    Maybe the Earth's gravity draws out more lava or liquid to create the Marias (there is a large amount of water on the Moon NASA finally admitted) There are moonquakes too. Those actions would cover up a lot of craters and not that had to imagine... Why didn't they think of that instead of coming up with such a weird conclusion? Here's another theory of mine; the near side of the Moon is more dense, duh.. That's why it always faces the gravity (us)

  7. Re:Thought Gene Shoemaker figured this out... by swillden · · Score: 2

    I'd be more inclined to trust the article if they hadn't claimed the moon is 40 earth diameters away from the earth...

    Meh. A simple error in the writeup, which I'm sure is not present in the scientific papers.

    http://lunarscience.nasa.gov/?question=3318

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  8. Re:Thought Gene Shoemaker figured this out... by swillden · · Score: 5, Informative

    Earth is 12,742 km in diameter. The moon is 363,104 km, 28.5 diameters, away at perigee, and 405,696 km, 31.8 diameters, at apogee.

    In round numbers the moon is 30 Earth diameters away.

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  9. Theory only works for perfect tidal locking by American+Patent+Guy · · Score: 2

    Yes, this theory makes sense if the moon is perfectly tidally locked. However, that isn't likely. The "far side" of the moon has been that only in human history: only a few thousand years. We're talking about billions of years. All that would be needed is a few centimeters creep per year and the far side would become the near side in the course of millions of years.

    This theory doesn't explain how the marias happen to all be on the near side presently given this creep. It also does not account for the likelihood that the warming would have been across the entire moon with this creep. It also does not account for the obvious fact that there are two kinds of surfaces on the near side on the moon: if this warming had been the cause, the difference would be more semi-hemispherical in nature (warming entirely one-half of the surface of the moon) -- the marias cover a lot less than that.

    My bogus detector is bleeping loudly