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Thread: If the Moon was the size of Mercury and much closer (ex:half the distance away) ?

  1. #1 If the Moon was the size of Mercury and much closer (ex:half the distance away) ? 
    Forum Cosmic Wizard icewendigo's Avatar
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    Hi there, I have a question for the physics and astronomy enthusiasts:

    IF the Moon had been both more massive (lets say the size of Mercury) and closer to the earth (lets say half the distance)

    1- What effect could this have had on space exploration of the moon? (how easier if at all would it have been to launch stuff in low earth orbit when a launch site and time was aligned with the closer massive mercury moon, and how much easier would it have been to send probes and astronauts to the moon?)


    2- What potential effects could that have had on Earth's environment? (More amplitude with Tides? More eclipses? etc)




    And if that doesn't make much of a difference, then lets raise the ante to: What if Mars was orbiting Earth at half the distance of the Moon?
    Could a cannon ball fired from a pirate ship on earth reach mars when Mars would be right above or reached the Earth if it were fired from Mars?




    thanks


    Last edited by icewendigo; December 1st, 2017 at 10:26 AM.
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    Forum Radioactive Isotope Paleoichneum's Avatar
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    Im pretty sure that the two (or three) would have been pulled together into either an asteroid belt, or a conglomeration planet formed from the collision of the three...


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  4. #3  
    Forum Cosmic Wizard icewendigo's Avatar
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    (For the sake of discussion, pretend the planets managed to orbit each other without breaking etc and that you had a mercury or mars sized planet in close proximity to the earth.)
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    If the Moon got _much_ closer to Earth tides would pull it apart. If it got a little closer, or more massive, then tides would increase. It would not be significantly easier to get to, since escape velocity would not change by much. You could never fire a cannonball and reach anything in orbit in the cases you describe.

    For a fictional treatment of the above questions, read Forward's "Rocheworld" (two planets very close to their Roche limit, the limit at which the tides destroy the planets.)
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    Forum Cosmic Wizard icewendigo's Avatar
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    thanks now i get it.

    So the type of planet that could have a somewhat earth like biosphere and on which space exploration would be easier would be a planet somewhere between the size of Earth and Mars?

    If our moon orbited mars how much closer could it be, and would the lower gravity of the mars like planet and closer proximity of a moon-like moon make it much easier to get people on the moon or not much different?
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  7. #6  
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    Quote Originally Posted by icewendigo View Post
    So the type of planet that could have a somewhat earth like biosphere and on which space exploration would be easier would be a planet somewhere between the size of Earth and Mars?
    Earthlike in what respect? In terms of atmosphere, temperature and hydrosphere? In that case, you'd hit a lower limit where gravity is insufficient to retain the air against thermal motion. To be technical, the escape velocity must be well above the RMS average speed of molecules in the atmosphere. (Which means that colder planets can be smaller and still retain an atmosphere.)

    More in a minute.
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