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Space Science

What Would Happen If the Moon Crashed To Earth? 68

Posted by timothy from the pissed-off-roaches dept.
angkor writes: "What would happen if the Moon crashed into the Earth? We'd die. But there seem to be a lot of variables involved in answering this. I wonder if /.ers have any other ideas..."
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What Would Happen If the Moon Crashed To Earth? More

What Would Happen If the Moon Crashed To Earth?

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  • The subject says it all really...
    • Well yeah, that's true, but that wasn't the question. It was a hypothetical question. "What Would Happen If the Moon Crashed To Earth?" So we are to assume that for whatever reason it will. It's neat to think about. I'd love to see a large scale computer simulation of this, but since it would have little practical value I doubt that it will get done for a very very long time.
    • If you'd read the article, you'd realize that the Computer (?!?) scientist who answered the fifthgrader's question went over why it was much more likely that the sun would reach the end of its life cycle or we'd be hit by an asteroid before the moon crashed into us.

      One interesting fact he mentioned is that the moon's gravity is very slowly lengthening the Earth's day, something that will probably have a significant impact on life on the planet if it continues for long enough.

  • Surreal celestial questions. (Score:5, Funny)

    by Christopher Thomas ( 11717 ) on Thursday July 04, 2002 @10:49PM (#3824783)
    The article pretty much covered why the moon won't ever hit the Earth (and what would happen if Q snapped his fingers and it did), so I won't touch that.

    However, this does remind me of a very, very bizzare conversation I and several others had a couple of years back (while waiting for food at a restaurant, and pondering the rolls).

    Q: What would happen if you had an entire planet made out of bread?

    Getting the answer was a very amusing thought-experiment. It turns out that you'd eventually end up with a bacteria-infested planet with a large diamond core, a mantle of uncertain composition, a crust of tar with seas of complex hydrocarbons and carbohydrates, and an atmosphere of methane and water vapour.

    So, I invite similarly bored slashdotters to consider similar questions involving other materials, or other interesting celestial thought-experiments.
    • Q: What would happen if you had an entire planet made out of bread?

      "We've just landed here on what cap troopers are calling the 'Big Bun' with the 6th Mobile Infantry Division. It's an ugly planet, a bread planet, a planet hostile to life as we know it...AAAAAAAAARRRRRGGGHHH!!!"

      Seriously, though, wouldn't its moon be a huge pat of butter?
    • regarding your hypothetical "bread-planet"

      why a diamond core ?

      oxygen is heavier, and at large densities you would probably get some metalic phase which is not solid state.

      come to think of it hyper-dense carbon should also be different than usual diamond, as the E part of the Gibbs free energy F=E-TS will be mostly a function of the density (r^-12 part of leonard-gibbs potential) and not of the chemical connection. (=> disordered state, pseudo-liquid)
      • why a diamond core ?

        Because diamond is the more compact form of carbon (hence its formation from other allotropes under pressure), and I'm assuming that carbon is more abundant than the other elements composing bread.

        oxygen is heavier, and at large densities you would probably get some metalic phase which is not solid state.

        Hmm. Diamond outer core? :)

        come to think of it hyper-dense carbon should also be different than usual diamond, as the E part of the Gibbs free energy F=E-TS will be mostly a function of the density (r^-12 part of leonard-gibbs potential) and not of the chemical connection. (=> disordered state, pseudo-liquid)

        My understanding was that diamond was stable up to surprisingly high pressure. The only thing that would be more compact than it would probably be some kind of metallic state with a spherical close-pack structure. Is a planet's core pressure enough to force diamond to convert to that kind of structure? (I don't have a phase diagram of carbon's allotropes handy.)
    • How about a universe where Uranium-235 replaced hydrogen..
    • A Diamond core? That certainly is plausable, but how big of a bread-planet does that require?

      On a slightly related note, check out this article [slashdot.org] from last month.
      • A Diamond core? That certainly is plausable, but how big of a bread-planet does that require?

        Not that big. We can form diamonds in hydraulic presses, so the pressure's pretty low on a planetary scale.

        On a slightly related note, check out this article [slashdot.org] from last month.

        That article made my head hurt :). I didn't see a convincing argument for atoms being sufficiently mobile for the proposed concentration of actinides in the core. The paper linked to cited other papers... but most of those were by the same authour. This is suspicious (it suggests that nobody else thinks the authour's work was worth following up on).
        • diamonds in a hydraulic press? granted, they're not going to be very big diamonds, but do you have more details/links involving how they achieved this? this ranks right up there with my curiosity of making artificial rubies in the microwave.
          • Google it, it shouldn't be hard to find. I saw a documentary on it once. NOVA I think. It is evidently very very hard to do. Most of the early ones (and the current cheap ones) turn out brown or yellow. They can make good clear ones that are indistinguishable from real ones except that they glow under UV light.
    • Earth == bread
      Moon == cheese
      Collision == very large grilled cheese sandwich.
    • Here's a vaguely related question.

      What happens if you heat bread in a vacuum? If you heat bread in atmosphere, it gets toasted -- the surface of the bread oxidizes, basically. In a vacuum, however, it would simply get warmer but there shouldn't be any kind of chemical reaction until it gets to -- dare I say it? -- the melting point of bread!

      So in theory, bread heated in a vacuum should eventually become liquid or vapor. Am I even close to being right?

      • I'm nowhere near an expert on this kind of thing, but I believe there would be several intermediate steps before the bread turned into vapour.

        The reason is that bread is made up of a bunch of different elements, and all have their own temperatures at which they turn into liquid and then gas. Thus, if you increased the temperature slowly enough, you could see some elements seperating from the bread mass before others.
      • What happens if you heat bread in a vacuum? If you heat bread in atmosphere, it gets toasted -- the surface of the bread oxidizes, basically. In a vacuum, however, it would simply get warmer but there shouldn't be any kind of chemical reaction until it gets to -- dare I say it? -- the melting point of bread!

        Unforunately, bread doesn't do anything this fun when heated :).

        In vacuum or in an inert atmosphere, you'd get chemical transformations long before any melting occurred. Sugar and starches would shed water to become mostly carbon, and the other varied building blocks would turn the bread loaf into something resembling tar before it started boiling.

        In vacuum, the water would diffuse into space immediately, and the other hydrocarbons would follow slowly (much lower vapour pressure, so less mass flow). You might have a brittle sponge-like mass of carbon left over.

        In an inert atmosphere at normal pressures, the water will boil off as steam, but as long as you're in a closed container most of the medium-to-heavy hydrocarbons will stay put once a small amount has boiled into the air (it stops boiling when the partial pressure of hydrocabons in the air equals the vapour pressure).

        Kind of neat to see what would result, though :). For an approximation, pour concentrated sulphuric acid on to the loaf. That catalyzes the extraction of water enough that it'll happen at room temperature, and it'll release enough heat to boil off the other volatiles. Doing this with sugar is a standard chemistry demo.

        [NOTE: I can't emphasize too much how much respect you should have for concentrated acids. Wear protective gear, and use long tongs if possible, because concentrated sulphuric will eat through almost anything except glass and ceramics.]
  • ...and he lives at the North Pole and would save the world from the impending moon.

    The only physics Computer Science majors should comment on is maybe a brief discussion on the issues of electrons, physical limitations of spinning platters, and maybe what would happen if the dvd were to crash into the cd-rom.

  • pluto & charon? (Score:3, Interesting)

    by klparrot ( 549422 ) <klparrot@ho[ ]il.com ['tma' in gap]> on Friday July 05, 2002 @01:09AM (#3825467)
    Relative to the size of its home planet (the Earth), our Moon is the largest moon in the solar system.

    What about Pluto and Charon? Aren't they closer in size to each other than Earth and the Moon?

    Yes; check out Nine Planets [arizona.edu] (look at Earth, The Moon, Pluto and Charon). Here are the diameters:

    __________ Diameter
    Pluto _____ 2274 km
    Charon ____ 1172 km
    Earth ____ 12756 km
    The Moon __ 3476 km

    This is a diameter ratio of about 1/2 for Charon/Pluto and 1/4 for Moon/Earth.

  • My own CNC's (cocktail napkin calculations)... (Score:5, Informative)

    by Tsar ( 536185 ) on Friday July 05, 2002 @01:35AM (#3825566) Homepage Journal
    ...indicate that, assuming the Moon's orbital momentum were bled off at some reasonable (!) rate, that it would spend sufficient time within its Roche limit (5.5*2.42/3.34 = ~4 earth radii) to be torn to bits and redistributed into a massive, chunky ring. Once that transformation was accomplished, the Earth's surface would rapidly restabilize; since the ring would have a somewhat evenly distributed mass, its major tidal effect would be to increase Earth's equatorial bulge.

    Of course, the large number of collisions in NEO among kilometer-and-greater-diameter objects would result in many thousands of catastrophic KT-magnitude impacts, meaning that any current life on earth would be kaput without a primary lunar impact ever occurring.

    Mr. Bailey answered this question well, but seemed to believe that this kind of event was impossible. I'd suggest running an N-body simulation in which a small, massive object such as a black hole passes near the Earth-Moon system, in such a way as to impart a differential acceleration to the two bodies. It's easy to find (by trial and error, if need be) the appropriate criteria for a fly-by that would drop the Moon right in our laps, with little or no lateral motion. I'd guess that this was probably the kind of impact that the questioner envisioned.

    Remind anyone else of the climactic scene of When Worlds Collide [imdb.com]?

  • What really happened.. (Score:3, Interesting)

    by fluffy666 ( 582573 ) on Friday July 05, 2002 @04:30AM (#3826151)
    The curent theory of moon formation is that when Earth has about 90% of it's current mass (~4.5 billion years ago, or 50ma after the start of the solar system), a planetoid about the size of mars hit at a glancing angle. This gave us an enhanced metal core (original core+core of the other planet), blasted enough rock vapour into space to create the moon, and melted the entire planet.

    It's safe to say that if you were on the surface of the earth prior to this, watching the incoming planet, you'd probably need a change of underwear.
  • I was listening to an NPR show quite
    awhile ago, (about 1-1 1/2 years ago i believe)
    They were talking about the moon ad said
    something to the effect that it will eventually
    drift out of earth's orbit.

    I believe the number quoted was somewhere between
    100,000 to 150,000 years from now.....

    • (* I was listening to an NPR show quite
      awhile ago, .....
      They were talking about the moon and said
      something to the effect that it will eventually
      drift out of earth's orbit.....I believe the number quoted was somewhere between 100,000 to 150,000 years from now..... *)

      My understanding is that the moon is drifting away from earth at the rate of about 4 inches a year. It is stealing rotational momentum from Earth, and thus the Earth's rotation is slowing. It used to be something like 12 hours a day way back, and the moon was much closer.

      It might get further away, but it will still be around when the Sun goes Nova and swallows it all anyhow.
      • >It might get further away, but it will still be around when the Sun goes Nova and swallows it all anyhow.

        Except the earth will probably not be swallowed when the sun goes off main sequence. It turns out that the astronomers who first suggested this neglected the fact that the sun will have radiated a significant portion of its mass as light during the billions of years left in its lifespan. As the sun loses its mass, the planets will gradually move further away from the sun, so the Earth will live to see the Sun become a white dwarf. Still, the Earth will be pretty toasty by that time, and will probably have lost its atmosphere to the solar wind long before that (once the Earth's core cools and we lose our magnetosphere.)
      • There's interesting circumstantial evidence that Earth's days were once longer. People and animals left to themselves in deep cave systems (ie completely isolated from sunlight) seem to all settle on a 25-hour day.

        Velikovsky's cosmic ballet explains this rather well. It's a pity it's become such an albatross that nobody's spending any time reworking it these days, because it seems fairly obvious (especially after Shoemaker-Levy and in light of things like Saturn's very young rings) that our solar system ain't the peaceful celestial meadow that many people like to make it out to be.

        I for one would be a lot more comfortable knowing how other objects in my solar system behaved under borderline situations, and fear of being branded a nutcase seems to be stopping science in general from investigating a lot of interesting stuff along these lines.
        • Really? Where did you see this evidence? Everything I've ever read points at a 19 hour day back in the early dinosaur days and slowing ever since then.
  • Thats where I keep all my stuff.
  • Given that we know, for certain, that the moon is made of cheese (this is as obvious as the fact that the universe revolves around the earth), the results are simply deduced:

    We would all be cheesed off.

    Thank you. Thank you Very Much.

  • The first has already been mentioned, and that is that Charon and Pluto are closer in size than the Earth and Moon. The second I don't think has been mentioned yet: the moon does not have "a cold, solid core". The August issue of Discover magazine points out a few reasons why we beleive that the Moons core is at least partially molten in the article "Nuclear Planet" (well, something like that, the title may have been a bit different).
  • According to an N-body simulation in which a small, massive object such as a black hole passes near the Earth-Moon system, in such a way as to impart a differential acceleration to the two bodies. The moon would drop from orbit and collide with a force of 10000 kilodinojoules into your eye like a big-a pizza pie.

    That's amore.

    At that point you'll sing "Vita Bella".

  • uhh... duh. (Score:4, Funny)

    by Patrick13 ( 223909 ) on Saturday July 06, 2002 @06:58PM (#3834563) Homepage Journal
    didn't anyone see the scientifically accurate movie The Time Machine [imdb.com]. When the moon collides with the earth, part of the population will flee underground and evolve into these freaky hyper-predator humanoids called morlocks. The fragmented remains of the surface-dwelling humans will create an idyllic proto society with neo-lithic science and incredible basket weaving skills.

    sheesh. i don't know why questions like this even get posted. The movie only just came out this spring.
  • Considering the moon is moving away from the earth, I think, if the moon were to crash into the earth, then pigs may fly, and hell just might freeze over as well...

    Thats just a guess though...
  • is if the moon crashed into the earth and everyone died and no one was left behind to tell about it... would it still make a sound?
  • Sounds like the old musings of Dave (Milk Milk Milk!). He would walk up to random people on the street and fire off the following questions, high speed, non-stop:

    Which way's up?
    What color's blue?
    What if the moon fell down?
    What if people were little yellow squares and dogs were red circles?
    What's your mom's name?
    What's your dad's name?
    What's your social security number?
    What color is your cat?
    What flavor is your dog?
    What shape is your mailbox?
  • I can't believe this. You all are making light of a very serious question involving mathematics of orbits, and what kind of long term solar system damage would occur should the moon (I assume we are talking about our moon, here), crash into the Earth. And all some of you do to answer this serious question is make jokes about things they learned from "Thundarr the Barbarian" or something. Well, not me.

    I want to know the media angle.

    This would be a godsend to Fox News and the New CNN. Ratings aplenty. All kinds of pundits speculating everything as the large death-ball looms closer. You heard me right: "death-ball." And people would be glued to their TVs, and advertising revenues would soar.

    "Pepsi presents: Armageddon. The choice of a lost generation."

    CNNfn would want to know how this would affect stock prices. There would be the usual gang of idiots all pointing their financial fingers in 20 different directions. Some would see the stock market plummet as people cashed out. Or leveled as people just gave up hope, because you can't take it with you. Maybe it would even increase, says a man who just bought 20billion shares of PepsiCo, because of all the ad revenue.

    CSPAN, with both of their cameras on 24/7, would show the last senators and representatives discussing how THEY should get more disaster relief to their state. Senator Gramm has taken the floor, demanding more disaster relief since the DFW corridor has taken a beating as it is in the dying IT market and with their citizens appearing on every other episode of "C.O.P.S." And now this! Probably a liberal plot to move the tech corridor to Virginia, he says.

    Fox news gets a poll:

    - Thinks the world is going to end: 55%
    - Thinks the world is going to recover: 22%
    - Thinks the moon is made of a stinky green cheese: 62%
    - Hopes it doesn't crash into their state: 95%
    - Knows it doesn't matter where it crashes, the world will blow up anyway: .05%
    - Thinks Senator Gramm is made of a stinky green cheese: 12%
    - Blames the Democrats: - 45%
    - Blames the Republicans: - 45%
    - Blames Senator Gramm: - 62%
    - Blames the reduction of "Pro-gravity" initiatives: - 5%
    - Said, "What moon?" - 10%
    - Said, "No foolin'? Crashin' into the Earth? Damn!" - 10%
    - Said, "I don't care, as long as I don't have to clean it up!" - 10%
    - Thinks this will postpone the Oscars - 42%
    - Thinks the polls are calculated incorrectly: - 129%

    Nickelodeon will have a Linda Ellerbee special called, "You didn't eat enough vegetables, and now we're all gonna die, you brats!" Sesame Street will have a very special episode where Dr. Philip Morrison explains gravity wells to Elmo. Parents petition books stores to remove the "inappropriate and disturbing" book, "Good Night Moon."

    Howard Stern will admit it was all an act to detract from his effeminate curly hair. Then he tells fart jokes until the studio or the moon's crash cuts him off the air.

    Evangelical Christians will be smug, say the bible predicted this with a lot of vague interpretations, and eventually blame gay people. Gay people will blame stereotypes. Stereotypes will blame the press, who will blame each other on the next 20/20. Jack Chick will suddenly admit his campaign and tracts were all a joke started by a bet with the late Anton LaVey on who could repel the most people from Christianity in the shortest time possible. He won.

    In the end, the media will finally get what it wants, and while the moon and the Earth smash into each other like melons in a mosh pit, people will still be arguing about whether this is all just hype.
  • The question should be "What would happen if the Earth crashed into the Moon?"...
    Geesh, how do you expect to get intelligent answers, when you ask the wrong silly question.
    RTFM (Reverse the Freaking Moon)
  • Been mention here before, but here's a lengthy read [theforce.net] - part of a larger site from someone who has a great deal of time on his hands.

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