# Now lets put the moon on earth **URL:** \ **Category:** Factual Questions\ **Created:** [March 10, 2007, 12:17pm UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367 "2007-03-10T12:17:42Z")\ **Posts on this page:** 20\ **Page:** 3
**Author:** ![kanicbird](https://avatars.discourse-cdn.com/v4/letter/k/5f8ce5/32.png) [@kanicbird](https://boards.straightdope.com/u/kanicbird)\ **Post date:** [March 11, 2007, 6:14pm UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/41 "2007-03-11T18:14:23Z")
The moon is balanced about it’s own center of gravity, that would shift in this case and parts of the moon that were in compression would now be under tension. I’m not sure about moon rock, but many things that can withstand enormous compressive forces fail easially in tension - so WAG # 1 the moon would fall into a big ‘lump’. The second thing to consider is the pressure that the moon would exert on the earth (yes this goes both ways) The actual PSI that the moon is exerting on the earth because of the mass of the moon above it will exceed the ability of the crust to support it. My wag is the crust would bend and break as the liquid core is displaced, causing great pressure in the liquid core, which will find it’s way out to the surface. In short I think it’s a very bad idea. ---
**Author:** ![msmith537](https://avatars.discourse-cdn.com/v4/letter/m/d9b06d/32.png) [@msmith537](https://boards.straightdope.com/u/msmith537)\ **Post date:** [March 11, 2007, 6:58pm UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/42 "2007-03-11T18:58:20Z")
[QUOTE=Noone Special] [_Rocheworld (Flight of the Dragonfly)_](http://en.wikipedia.org/wiki/Rocheworld) By [Robert L. Forward](http://en.wikipedia.org/wiki/Robert_Forward). The two planets there form a [Double Planet](http://en.wikipedia.org/wiki/Double_planet), with the two components close enough to share an atmosphere. ISTR that the relationship was described in pretty minute mathematical detail in the book, and that somehow it worked out that the two planets were each outside the Roche Limit of the other [/QUOTE] I wish people would stop using sci-fi books as reference material. Wikipedia gives a need little chart: > **[Roche limit](https://en.wikipedia.org/wiki/Roche_Limit)** > > In celestial mechanics, the Roche limit, also called Roche radius, is the distance from a celestial body within which a second celestial body, held together only by its own force of gravity, will disintegrate because the first body's tidal forces exceed the second body's self-gravitation. Inside the Roche limit, orbiting material disperses and forms rings, whereas outside the limit, material tends to coalesce. The Roche radius depends on the radius of the second body and on the ratio of the bo Th... Body Satellite Roche limit (rigid) Roche limit (fluid) Distance (km) R Distance (km) R Earth Moon 9,496 1.49 18,261 2.86 So basically, depending on how fluid the moon is, tidal forces will cause it to break up once it is within 1.5 to 2.9 Earth radii of the center. So I suspect that if the Moon were magically teleported onto the Earth’s surface, it would immediately break apart due to tidal forces. ---
**Author:** ![Noone\_Special](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/noone_special/32/2863_2.png) [@Noone\_Special](https://boards.straightdope.com/u/Noone_Special)\ **Post date:** [March 11, 2007, 7:26pm UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/43 "2007-03-11T19:26:48Z")
[QUOTE=msmith537] I wish people would stop using sci-fi books as reference material. [/quote] You’re right of course – but I wasn’t using the book as a reference. My post was in response to a request for a name and author (of, I think, _Rocheworld_.) > [@](#): > > Wikipedia gives a need little chart: > [Roche limit - Wikipedia](http://en.wikipedia.org/wiki/Roche_Limit) > > Body Satellite Roche limit (rigid) Roche limit (fluid) > Distance (km) R Distance (km) R > Earth Moon 9,496 1.49 18,261 2.86 > So basically, depending on how fluid the moon is, tidal forces will cause it to break up once it is within 1.5 to 2.9 Earth radii of the center. > > So I suspect that if the Moon were magically teleported onto the Earth’s surface, it would immediately break apart due to tidal forces. OK. Thanks for the information; that’s what I was originally looking for! 🙂 ---
**Author:** ![Subway\_Prophet](https://avatars.discourse-cdn.com/v4/letter/s/ecb155/32.png) [@Subway\_Prophet](https://boards.straightdope.com/u/Subway_Prophet)\ **Post date:** [March 11, 2007, 8:36pm UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/44 "2007-03-11T20:36:08Z")
[QUOTE=Harmonious Discord] Onw Scifi author wrote about two planets close to each other that transfered water and atmosphere sometimes. The expedition checking out one planet finds themselves on the other, with the mothership on the original planet, and them with a planetary exploring transport on the second. It was interesting, but I don’t know the book or author now. [/QUOTE] I believe it’s a series by Bob Shaw - I remember _The Ragged Astronauts_ had a setting similar to this. ---
**Author:** ![pmwgreen](https://avatars.discourse-cdn.com/v4/letter/p/edb3f5/32.png) [@pmwgreen](https://boards.straightdope.com/u/pmwgreen)\ **Post date:** [March 12, 2007, 3:20am UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/45 "2007-03-12T03:20:05Z")
[QUOTE=Meurglys] It’s over 2000 miles in diameter! Even if it did fit into the Pacific somewhere (Hawaii might get in the way a bit!) it’s going to stick up over 2000 miles into space! And I guess it would displace thousands of cubic miles of seawater, which would raise the world’s sea levels a touch, I expect… [/QUOTE] The numbers are amazing. The moon is 3500 km across. The ocean is about 4 km deep. You might as well drop it on antarctica, which is 25km closer to the center. Also the space shuttle orbits at a height of only hundreds of kilometers, so it will have to fly around the moon, looking up at it at an angle pretty much the same as us unlucky ground dwellers. As for the ISS, well Bush said he wanted a base on the moon. ---
**Author:** ![Jinx](https://avatars.discourse-cdn.com/v4/letter/j/c6cbf5/32.png) [@Jinx](https://boards.straightdope.com/u/Jinx)\ **Post date:** [March 12, 2007, 3:30am UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/46 "2007-03-12T03:30:15Z")
First, you have to do an Environmental Impact Statement, and hope you can demonstrate a Finding of No Significant Impact (FONSI)… 😃 ---
**Author:** ![commasense](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/commasense/32/3017_2.png) [@commasense](https://boards.straightdope.com/u/commasense)\ **Post date:** [March 12, 2007, 3:36am UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/47 "2007-03-12T03:36:21Z")
[QUOTE=Beware of Doug] This is a terrible idea, and I, for one, am against it. Whom do I write? My Congressman? NASA? MENSA? Fox News? A competent mental health professional? [/QUOTE] You know, it never fails. Someone suggests an innovative idea, and instantly it meets with knee-jerk opposition. I say let’s give it a chance and see how it works out. If we don’t like it, we can always put it back where it was. Sheesh! Live a little! > [@Harmonious Discord](#): > > One Scifi author wrote about two planets close to each other that transfered water and atmosphere sometimes. The expedition checking out one planet finds themselves on the other, with the mothership on the original planet, and them with a planetary exploring transport on the second. It was interesting, but I don’t know the book or author now. Not the one you were thinking of, but Italo Calvino’s collection _Cosmicomics_ includes a short story called “The Distance of the Moon.” It’s set in a mythical time when the Moon’s orbit was so close that when it approached, you could climb up on a ladder, jump up, and float up to it and spend the afternoon there. But it’s moving farther away, and it gets harder to get there or back. He tells a charming little romantic tale of love and longing between the earth and the moon. I highly recommend the book. Each witty little story starts with a scientifically accurate fact about the formation of the universe, the solar system, or life on earth, and tells a tale about how it affected the people (with names like Qfwfq and Mrs. Vhd) who were around back then. ---
**Author:** ![The\_Hamster\_King](https://avatars.discourse-cdn.com/v4/letter/t/8edcca/32.png) [@The\_Hamster\_King](https://boards.straightdope.com/u/The_Hamster_King)\ **Post date:** [March 12, 2007, 4:30am UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/48 "2007-03-12T04:30:28Z")
I did some rough, back-of-the-envelope calculations. The moon in that configuration has about 10^30 joules of potential energy. Gravity will almost immediately compress the two bodies into a single spherical mass. (I’m guessing it wouldn’t take more than a few hours – at that scale solid rock will simply behave like a fluid.) That means most of that potential energy will be converted to heat. That’s more than enough energy to turn the entire crust of the new body molten. Even without the kinetic energy of a high-speed impact it would be the end of all life. In fact, the resulting new planetary body in Earth’s orbit probably wouldn’t even retain any traces of our current continents, let along any evidence that humanity once existed. ---
**Author:** ![Subway\_Prophet](https://avatars.discourse-cdn.com/v4/letter/s/ecb155/32.png) [@Subway\_Prophet](https://boards.straightdope.com/u/Subway_Prophet)\ **Post date:** [March 12, 2007, 2:14pm UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/49 "2007-03-12T14:14:04Z")
[QUOTE=Pochacco] Even without the kinetic energy of a high-speed impact it would be the end of all life. In fact, the resulting new planetary body in Earth’s orbit probably wouldn’t even retain any traces of our current continents, let along any evidence that humanity once existed. [/QUOTE] But my CD collection will still be good, right? I mean, I’ve been working on my collection for _years_. ---
**Author:** ![Ludovic](https://avatars.discourse-cdn.com/v4/letter/l/7ab992/32.png) [@Ludovic](https://boards.straightdope.com/u/Ludovic)\ **Post date:** [March 12, 2007, 2:38pm UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/50 "2007-03-12T14:38:29Z")
I for one welcome our new lunal overlords. ---
**Author:** ![Baldwin](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/baldwin/32/7264_2.png) [@Baldwin](https://boards.straightdope.com/u/Baldwin)\ **Post date:** [March 21, 2007, 2:35pm UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/51 "2007-03-21T14:35:27Z")
[QUOTE=AWB] Now if, remarkably, neither broke apart, the center of mass of the Earth/Moon would shift towards the Moon part, and so too would the direction of “down” to those that weren’t on the “top” of either. Total gravity would increase overall. [/QUOTE] No, the center of mass would move the other way, closer to the Earth’s core than it already is. I guess if you _had_ to extinguish all higher life on Earth, this would be a neat way to do it. Too bad about those adorable Koala bears, though. ---
**Author:** ![CalMeacham](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/calmeacham/32/35_2.png) [@CalMeacham](https://boards.straightdope.com/u/CalMeacham)\ **Post date:** [March 21, 2007, 2:42pm UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/52 "2007-03-21T14:42:50Z")
**robby** writes: > [@](#): > > Also, for what its worth, Mercury and Venus are not very good examples. They’re both tidally locked with the Sun. ??? What do you mean by this? Neither Venus nor Mercury are “tidally locked” with the sun in the usual meaning of the phrase ( meaning that the same face of the planet is always toward the sun, as the same face of the moon is always toward the earth). There was a time when it was believed of Mercury, but that ended back in the 1950s. I don’t recall ever reading it to be believed of Venus. ---
**Author:** ![Jake](https://avatars.discourse-cdn.com/v4/letter/j/f475e1/32.png) [@Jake](https://boards.straightdope.com/u/Jake)\ **Post date:** [March 21, 2007, 4:20pm UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/53 "2007-03-21T16:20:02Z")
At least we wouldn’t have to listen to all this bitchin’ about the Ozone Layer anymore. 🙂 ---
**Author:** ![Giles](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/giles/32/60_2.png) [@Giles](https://boards.straightdope.com/u/Giles)\ **Post date:** [March 21, 2007, 4:31pm UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/54 "2007-03-21T16:31:54Z")
[QUOTE=Jake] At least we wouldn’t have to listen to all this bitchin’ about the Ozone Layer anymore. 🙂 [/QUOTE] But you’ll still have people complaining about global warming. ---
**Author:** ![Ludovic](https://avatars.discourse-cdn.com/v4/letter/l/7ab992/32.png) [@Ludovic](https://boards.straightdope.com/u/Ludovic)\ **Post date:** [March 21, 2007, 5:18pm UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/55 "2007-03-21T17:18:52Z")
[QUOTE=Giles] But you’ll still have people complaining about global warming. [/QUOTE] What is this “globe” of which you speak? ---
**Author:** ![Chronos](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/chronos/32/134_2.png) [@Chronos](https://boards.straightdope.com/u/Chronos)\ **Post date:** [March 21, 2007, 5:19pm UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/56 "2007-03-21T17:19:31Z")
Well, Mercury does have a harmonic lock to the Sun, and Venus is almost locked to the Sun, and would be, except that there’s a harmonic lock to the Earth, of all things, holding it back. ---
**Author:** ![Autolycus](https://avatars.discourse-cdn.com/v4/letter/a/22d042/32.png) [@Autolycus](https://boards.straightdope.com/u/Autolycus)\ **Post date:** [March 21, 2007, 5:21pm UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/57 "2007-03-21T17:21:01Z")
[QUOTE=Chronos] Well, Mercury does have a harmonic lock to the Sun, and Venus is almost locked to the Sun, and would be, except that there’s a harmonic lock to the Earth, of all things, holding it back. [/QUOTE] Please explain. ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [March 21, 2007, 5:55pm UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/58 "2007-03-21T17:55:59Z")
[QUOTE=CalMeacham] **robby** writes: ??? What do you mean by this? Neither Venus nor Mercury are “tidally locked” with the sun in the usual meaning of the phrase ( meaning that the same face of the planet is always toward the sun, as the same face of the moon is always toward the earth). There was a time when it was believed of Mercury, but that ended back in the 1950s. I don’t recall ever reading it to be believed of Venus. [/QUOTE] [QUOTE=Chronos] Well, Mercury does have a harmonic lock to the Sun, and Venus is almost locked to the Sun, and would be, except that there’s a harmonic lock to the Earth, of all things, holding it back. [/QUOTE] [QUOTE=Autolycus] Please explain. [/QUOTE] From [here](http://en.wikipedia.org/wiki/Tidal_locking): > [@](#): > > Until radar observations in 1965 proved otherwise, it was thought that Mercury was tidally locked with the Sun. Instead, it turned out that Mercury has a 3:2 spin-orbit resonance, rotating three times for every two revolutions around the Sun; the eccentricity of Mercury’s orbit makes this resonance stable. The original reason astronomers thought it was tidally locked was because whenever Mercury was best placed for observation, it was always at the same point in its 3:2 resonance, so showing the same face, which would be also the case if it were totally locked. > > A curious aspect of Venus’ orbit and rotation periods is that the 583.92-day interval between successive close approaches to the Earth is almost exactly equal to 5 Venusian solar days (precisely, 5.001444 of these), making approximately the same face visible from Earth at each close approach. Whether this relationship arose by chance or is the result of some kind of tidal locking with the Earth is unknown. Also [here](http://en.wikipedia.org/wiki/Venus): > [@](#): > > Venus rotates once every 243 days – by far the slowest rotation period of any of the major planets. A Venusian sidereal day thus lasts more than a Venusian year (243 versus 224.7 Earth days). With respect to Mercury, I’m aware that the planet is not synchronously tidally locked with the Sun; however, it does have a “3:2 spin-orbit resonance,” which of course is no coincidence, and since the resonance is due to solar tidal forces, I would argue that it is a type of a tidal lock (though not a synchronous one, I grant). With respect to Venus, it’s orbital and rotational periods are very nearly the same. This is likely due to solar tidal forces. A hypothesized reason for why they are not exactly the same is tidal forces from the Earth. I think it is no coincidence that the two planets closest to the Sun apparently exhibit various forms of solar tidal locking. ---
**Author:** ![Will\_Repair](https://avatars.discourse-cdn.com/v4/letter/w/a698b9/32.png) [@Will\_Repair](https://boards.straightdope.com/u/Will_Repair)\ **Post date:** [March 21, 2007, 9:30pm UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/59 "2007-03-21T21:30:55Z")
[QUOTE=Subway Prophet] The Moon won’t roll; [/QUOTE] That’s reasurring. But I figured the Himalayas would stop it anyway. ---
**Author:** ![robby](https://sea3.discourse-cdn.com/straightdope/user_avatar/boards.straightdope.com/robby/32/11048_2.png) [@robby](https://boards.straightdope.com/u/robby)\ **Post date:** [March 22, 2007, 3:38pm UTC](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367/60 "2007-03-22T15:38:32Z")
[QUOTE=Will Repair] That’s reasurring. But I figured the Himalayas would stop it anyway. [/QUOTE] You’re probably being funny, but in case you are actually serious… The Himalayas are about 5-1/2 miles high. The diameter of the Moon is 2,160 miles. If the Moon were strong enough to roll (which it isn’t), it wouldn’t even notice the Himalayas. Of course, the Moon won’t roll, because it be too busy collapsing into the Earth. [Previous page](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367.md?page=2) [Next page](https://boards.straightdope.com/t/now-lets-put-the-moon-on-earth/395367.md?page=4)