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Could the Moon be the cooled remains of a planets core?

  1. Aug 1, 2011 #1
    I was reading an article over the weekend that the Moon has evidence of a "final" volcano on it's "far side." I am working on something that suggests the Moon would be too small to have had volcanoes, and this didn't fit with my assumption. I then reasoned that based on size, and based on the different types of cratering from impacts over time, that it would be a fair assumption to consider that the Moon is the now cooled core and is all that remains of a once thriving larger planet perhaps similar to ours. Could the Moon be the yolk of a once cracked egg type planet such as ours. Could we have had a twin?

    As the molten core took hits over time as it cooled, and finally perhaps one big hit causing a final volcano to erupt before final cooling of the entire mass. Has this possibility been considered? Is it realistic to assume such a scenario.

    Of course this assumption would suggest that a cataclysmic event occurred that caused the tectonic plates and all mass between the core and those plates to be thrown into space, only leaving the now cooled once molten core. What happened to the rest of the planet if this occurred?

    This is my second post on Physics Forums so I hope I am staying within the guidelines.
  2. jcsd
  3. Aug 1, 2011 #2


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  4. Aug 1, 2011 #3
    Thanks ryan_m_b I did post on the "ask a stupid question ..." forum on Saturday I believe it was. I only had one reply in my email but not yours.
    Anyway, I read that hypthothesis you referenced in wikipedia. It does mention that there are some unresolved concerns with that particular hypothesis. If that hypotheses is not accurate, could my assumption be considered valid? To add to that thought, could the Earth have had a twin and if so, how would that twin planet lose all it's mass except for the core. Again I'm suggesting that the Moon is a cooled core of a planet that could well have been similar in size to ours. Is the Moon about the right volume compared to what we assume the Earth's core to be?
  5. Aug 1, 2011 #4


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    There is no evidence that the Moon is the core of another planet. Firstly where would the rest of the mass go? Considering you are suggesting a planet of comparable mass to Earth ~6e24kg and the mass of the Moon is ~7.35e22kg where did the other ~99% of the mass of this planet go? If we were a double planet system at some point in the past any event that would have removed 99% of the mass of the other planet would have utterly decimated Earth.

    You assumption is not valid because there is no evidence for your assumption I'm afraid and a lot of evidence to suggest that the Moon formed out of the debris cloud of a large impact.
  6. Aug 1, 2011 #5


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    Further (in support of ryan_m_b):

    A core of a planet it traditionally the most dense portion of that body (being that highly dense materials settle closer to the central point of gravitation).

    The average density of the Earth (as a whole) is: 5.52 g/cm3
    The average density of the Earth's core is: 13 g/cm3

    In contrast, the average density of the moon is: 3.35 g/cm3

    Your theory would have to take into account how the "cooled core" of a planet could be so radically light given its origins. Even Saturn (the least dense planet in the solar system at 0.7 g/cm3) is likely to have a core of iron and nickel.

    Your idea, while possibly interesting, has no supporting evidence, and seems to contradict some routinely observable evidence.
  7. Aug 1, 2011 #6
    I appreciate your knowledge and the references on the subject.

    It was the scientific response mentioned in the article here, "http://www.time.com/time/health/article/0,8599,2085558,00.html that gave rise to my assumption because it appears these scientists seem to be suggesting that questions as to the origin have arisen in the penultimate paragraph of the article.

    In regards to your second point about density, I assumed density at the core was because of pressure by P equals m/v and assumed that if a core was exposed it would expand?

    I was just reading about Muller's CMB avalanche model here http://www.lbl.gov/Science-Articles/Archive/Phys-earth-core.html and his theories that related to the stripping of the core mantle boundary by an oblique impact vs. a more vertical impact.

    I was assuming that since Earth has tectonic plates that a very large impact could more readily dislodge matter because of the plate structure and that the planets would perhaps have been further apart in orbit prior to the impact. I also took a look to see if I could find what the trajectory of the debris field was when the rocket hit the comet in the "Deep Impact" mission to give a clue what path the debris might have taken after impact. It is not easy to find on the NASA Deep Impact Legacy Site that I can see.

    I'll leave it there for now as I have other more pressing problems to solve. Thank you for the feedback.
  8. Aug 1, 2011 #7
    Here is an excerpt (p.2) from the following pdf "Why the Moon is important for Solar System Science" that was submitted to The Inner Planets Panel, NRC Decadal Survey for the Planetary Sciences Division, Science Mission Directorate, NASA:

    Last edited: Aug 1, 2011
  9. Aug 1, 2011 #8


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    Firstly this is not a scientific article and you would be amazed at how distorted actually scientific discoveries can become in magazines and newspapers. I would advise you to find the original, peer-reviewed research. Secondly I don't see how that article helps your hypothesis, the volcano may or may not point to something we didn't know before but it hardly suggests that there is scope for an Earth sized planet that somehow disappeared.

    The inner core of the Earth is estimated to be 80% iron with the last 20% made up from nickel, lead, uranium and other trace elements. These elements have densities of ~7.8g/cm3, ~8.9g/cm3, ~11.3g/cm3 and 19.1g/cm3 respectively. I imagine that the severe temperature of the core is what gives rise to the density seen there. According to these numbers if the core was to cool it would actually shrink.

    Again you are going to have to provide some peer-reviewed research here. This CMB avalanche model still doesn't give any credibility to how 99% of your hypothetical planetary mass disappeared.

    It doesn't matter if the planet has tectonic plates or not you still need a fantastic amount of energy to remove 99% of the mass from a planet. I'm afraid that this planetary core hypothesis has no evidence and contradicts a lot we do know.
  10. Aug 1, 2011 #9
    Hi Jack.:smile: You have a great imagination.:biggrin: Never heard of the 'cracked egg type planet'. I do think the Earth and the Moon share a common thing:

    1. From the American Association for the Advancement of Science - Science is a peer-reviewed journal:
  11. Aug 2, 2011 #10
    Thanks for the reference.
  12. Aug 2, 2011 #11
    Interesting stuff. I talked to an Aeronautical Engineer from NASA about a year or so ago, he told me that when they impacted the Moon the reason water was identified was because someone had left a bottle of Naive water, ..sorry Evian water in the rocket. He was probably kidding right?
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