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Could a planet ever be split into two halves?

  1. Jun 27, 2010 #1
    Hi. Upon doing some research I’ve stumbled on this site. As someone very ignorant about the mechanics of the universe, I wonder if I could ask a very random question here. I am a writer, currently working on the premise of a novel which must adhere to the following brief: the story must be set on an ‘alternative’ Earth, one that, at some point, has gone down a different ‘trouser-leg of time’. Anything can be different, from a small subtle difference in Earth’s history, to a large, very evident one.

    The scenario I would like to build on is that Earth (being the same in every other aspect) has formed with a large set of extremely deep trenches (a massive fault zone) running in a very broken but also distinguishable line around its entire circumference. Visually, this would look like a line around the entire Earth.

    The novel is set in the present day.

    My question is, could there be any combination of factors, or any situation at all that would result in a planet (not necessarily Earth) being very slowly torn in two – either through external forces e.g. two opposing gravitational pulls, or by internal forces splitting the planet in half, gradually, over time.

    My mind has thrown up a couple of scenarios that are probably very unfeasible:

    I have read that a constantly fluctuating gravitational pull can cause a planet to distort again and again, creating friction and heat within the planet. Could this rising heat possibly contribute to a gradually expanding Earth, and therefore a growing fault line? Could a planet break into two halves because of this (assuming it has some sort of integral weakness) or would the break-up of Earth be an all-round affair, with it generally exploding over time? (Like WASP-12b).

    Or if there was a very large planet orbiting in tandem with the Earth, having a gravitational pull the opposite direction of the Sun’s, could this contribute to a slow pulling-apart, which might be most obvious in the equatorial or pole-to-pole trench growing larger?

    As you can see, I’m flailing around in a dark cupboard. Basically I need a scenario in which the planet is being pulled in two over a long period of time, hopefully a scenario that is at least a tiny bit credible.

    (The point is that the duality of human nature is reflected in this physical metaphor).
  2. jcsd
  3. Jun 27, 2010 #2


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    If you did it would just form two spherical planets - like a raindrop splitting, rememebr the earth is a liquid except for the crust
  4. Jun 27, 2010 #3

    Filip Larsen

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    The only scenarios I can think of that to some extend may approximate what you ask for, is a planetoid being pulled apart by tidal forces by a larger and nearby planet, or a planet being split into two after a major impact by another body of comparable size (although that probably won't quite fit your requirement of "slow pulling apart").

    If you want some details on the first scenario you can search for "Roche limit" while the second scenario more or less fits how we currently believe the earth-moon system was formed.
  5. Jun 27, 2010 #4
    A major impact did occur, and we call the uneven "split" our moon.
  6. Jun 27, 2010 #5
    It's pretty hard to have a story about people living on a planet that's being split in two when the split is essentially instantaneous and kills everything on the planet.

    Roche Limit's your best bet, but you won't get two even halves from it. It would be pretty much impossible for you to get a gravitational system that would neatly pull a planet in half. The configuration wouldn't be stable over a long enough time.
  7. Jun 28, 2010 #6
    Thank you very much Filip and Quisquis, your answers really helped. I've been looking at the Roche limit and you're right, that does best fit the scenerio - however it seems from what I've read that the sun's and Jupiter's Roche limit would be pretty much be inside themselves? For a planet like Earth.

    Anyway - thank you very much for your opinions, it's much appreciated. I'll have to have a rethink and possibly go with something completely different!
  8. Jun 28, 2010 #7
    You could go with orbiting a cool white dwarf; it's roche limit should be something you can work with. Then you'd need to explain why it's not hot though.

    It could have a dyson sphere put around it by mysterious long gone aliens!

    Just a couple of thoughts.
  9. Jun 28, 2010 #8
    I appreciate that this may be off topic, but the OP also needs to work with as many facts as possible.
    The mantle, which constitutes the bulk of the Earth is solid. The inner core is solid. Only the outer core is liquid. Small portions of the mantle, at shallow depth and where invaded by water from subduction zones, experience partial melting. However, this is in very small parts of the mantle and probably never constitutes more than 35% of the effected zone.
    In summary, the Earth is largely solid apart from the outer core.
  10. Jun 28, 2010 #9
    I think that's Ringworld :wink:

    Perhaps you could have them orbiting a barycenter, instead of being split, and the two worlds could have been formed from the same planetary disk?
  11. Jun 28, 2010 #10
    Here's a question then:

    Could two planets of completely equal mass and size orbit each other?

    If whatever hit the Earth to create the moon, instead, created two planets of exact same mass and size, is it feasible that they could orbit each other (or this 'barycenter') relatively closely, whilst also orbiting the sun, and both harbour a stable atmosphere/environment in which life could've formed?

    Or would there be issues with the two planets pulling each other in and colliding eventually?

    Edit: After doing a bit of reading I understand that if the distance between the 'twin' planets were the same as the Earth and Moon, the tidal forces would be way too strong for life to have developed. How far away would the twin planets have to be from each other for their atmospheres and environments to have developed into something at least relatively stable?
    Last edited: Jun 28, 2010
  12. Jun 29, 2010 #11
    Anything strong enough to tear a planet in two will most likely destroy life. The volcanic activity alone would destroy most everything, and the amount of ash thrown into the atmosphere would block out the sun for years.

    I've read if the earths tilt was a few degrees off in either direction life couldn't have formed... So basically I think you're going to have to work unrealistic events and science to keep with the theme of your novel. With that in mind, I think the 2 planet idea would have a good story to it. We didn't even see the craters on the moon until ~1640, imagine finding out the large body near us actually holds life; a surprising (to the people in the novel) yet expected (to the reader) twist would be that the life there evolved at nearly the same rate as ours or something. Or maybe they communicate with us first. Just some thoughts, I'll leave the story telling to you :)

    For an example on tidal forces, look up Jupiter's moon Io, it has ongoing volcanic activity from Jupiter's gravity twisting and churning the moons insides, and it's about the same size as our moon.
  13. Jun 29, 2010 #12
    I'm aware of the tidal forces effect on Io, and also on Enceladus. In regards to the twin planets, I'm aware that the split would destroy all life. But what I mean is a split happening instead of the one that created the moon - we're talking about proto-Earth stage, so surely life wouldn't come into it? There wouldn't be life to destroy back then.

    I'm assuming the impact that created the moon was catastrophic enough to create the ash and volcanic activity you describe, but life still evolved later on. I'm trying to find out whether it is possible for proto Earth to have been spilt into two more similarly sized chunks that orbited far enough away from each other to not have too adverse tidal affects.

    Also, only one of the planets would need to sustain life. The other could be slightly more barren if needs be, but feasible in terms of future colonisation.

    To be honest I think I might just have to work hard to suspend people's disbelief.
  14. Jun 29, 2010 #13
    Your last sentence is sage advice to all writers in the genre, but if you posit this impact or event billions of years ago, then yes it shouldn't interfere with the evolution of life. Hell, if Catherine Asaro's characters can "rotate out of our space" by "adding an imaginary component to velocity" I think you can fudge this one without guilt or worries. If this setup is critical to your storytelling, then I say make it work and focus on events more relevant to the day-to-day of your characters; that's what readers will focus on most anyway.
  15. Jun 30, 2010 #14
    You should check out the story Baxter wrote about the Pluto-Charon system, I think the short title was Ice Spiders.

    Basically the Pluto-Charon bodies orbit each other with the same side facing, so theoretically you could build a web between them, he wrote a story about the Pluto spring/summer when it makes it's closest approach to the sun, and briefly gains a wispy atmosphere. As the atmosphere rises, it catches the nets woven by the ice spiders, hauling them up to Charon, and if you catch just the right angle, you can see the strands of silk stretching between the two planets.
  16. Jun 30, 2010 #15
    That's good advice. Thanks all -the secret of good story telling lies not in the realism of the content, after all, but in the skill of the writer to make something out of what could be, essentially, nothing.
    Thanks to all for your help.
  17. Jun 30, 2010 #16
    seriously? I'm aware of their existence, but I've never read them.
  18. Jun 30, 2010 #17
    Oh you really should! *gushes*

    The premise (without spoiling) is not a full Dyson SPHERE, but a massive ribbon of one around a star. There are a number of species which have evolved, it deals with resources and the limitations of such a construct. It was, made by a long lost alien species...

    I can vouch for the first three novels of the series: all by Larry Niven.
  19. Jul 13, 2010 #18
    Could two planets of equal mass occupy the same orbit at a distance from each other so as to be visible one to the other, but having manageable gravity interaction.?
  20. Jul 13, 2010 #19
    I don't know what you mean by manageable gravitational interactions, but two planets or any masses can orbit a barycenter. See the 2-body problem.
  21. Jul 13, 2010 #20
    Tidal forces that are not destructive...

    I am speaking of two equal masses that occupy the same orbit around the sun, but do not orbit each other. It seems a highly unlikely condition, but was just wondering...
    A difference in masses would lead to unlike orbits wouldn't it?
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