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Thread: High mass high density super Earth

  1. #1
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    High mass high density super Earth

    The idea of Super Earths fascinates me. So I wanted to get input on this.
    In a calculator I created a planet with 2 Earth radii a density of 9 g cm/3 equaling 13.1 Earth masses. Now this is huge. I am curious if a massive planet like this can be habitable. How would life operate? Thanks 🙂

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    The force of gravity would be stronger, but that probably also means that the atmosphere would be thicker and the oceans would be deeper. The extra gravity probably wouldn't hurt marine life.
    Forming opinions as we speak

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    Before the thread got way off track in the middle, this was the best resource on this board for the question you asked.

    https://forum.cosmoquest.org/showthr...h-civilization

    If the gravity is high, the upper air will probably be H/He, but the lower atmosphere will be dense, heavy, and shallow in height (compacted closer to ground, except for H/He which will go very high).

    One other thing, the max radius for Super Earths seems to be 1.5-2, and for low-end mini-Neptunes seems to be 2-2.5. Unclear if you will get a Super-Earth like our Earth if you go over 2 radii.

    My guess is that the seas will be shallow in general, as high gravity crushes mountains and evens out valleys with landslides.

    Is this for an SF story? Just curious.
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    Quote Originally Posted by Roger E. Moore View Post
    My guess is that the seas will be shallow in general, as high gravity crushes mountains and evens out valleys with landslides.
    But a denser, larger world would have a much more active interior, resulting in more tectonic activity and scale variation than Earth. Taller highs, deeper lows. It's mostly erosion that flattens and fills.

    In fiction, Larry Niven's Jinx was a super-Earth with very low amounts of radioactive elements in its core, resulting in a cold solid interior. That allowed him to posit a smooth surface and oblong shape.
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  5. #5
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    Some worlds that big are rocky. A few mega Earths I looked at it rocky but bigger. Kepler 145b and K-266b are examples.

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    From my reading, if you are making up the Super-Earth, you can choose whether you want a tectonically active world or a dead one. It's a question of core vs. mantle balance, which apparently varies a lot in space so you can just pick the result and make the interior fit the bill. I'm still going to say you will get lower mountains and shallower valleys, particularly if the world is very active, again because of earthquakes and landslides. but also because of the sheer force of gravity. Will have to look up references to support my argument however.

    I would argue that small worlds are far more likely to have higher mountains and deeper valleys, with Mars being the leading example. No amount of earthquakes are going to reduce Mount Olympus or fill in Mariner Valley. More soon.
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    Quote Originally Posted by KTevolved365 View Post
    I am curious if a massive planet like this can be habitable. How would life operate? Thanks ��
    Define "life". Like human life or rugose squamous hexapods or what? Methane life or water life?
    Do good work. —Virgil Ivan "Gus" Grissom

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    Quote Originally Posted by Roger E. Moore View Post
    From my reading, if you are making up the Super-Earth, you can choose whether you want a tectonically active world or a dead one. It's a question of core vs. mantle balance, which apparently varies a lot in space so you can just pick the result and make the interior fit the bill. I'm still going to say you will get lower mountains and shallower valleys, particularly if the world is very active, again because of earthquakes and landslides. but also because of the sheer force of gravity. Will have to look up references to support my argument however.
    It was in Wikipedia.

    https://en.wikipedia.org/wiki/Super-Earth#Habitability

    See this source for details on flatter terrain on Super-Earths.

    https://www.scientificamerican.com/a...in-our-galaxy/

    Oh, crud, now behind a paywall.
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  9. #9
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    I looked up planets and apparently there are rocky planets though rare that are bigger than this scenario with Kepler 145b being 2.6 Earth radii and 37 Earth masses.
    https://www.hou.usra.edu/meetings/lpsc2018/pdf/1224.pdf
    Again these are kind of rare but possible it seems. But it is neat to see the varieties of worlds. Any life that can survive 3g. Is what I mean.

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    Quote Originally Posted by KTevolved365 View Post
    Any life that can survive 3g. Is what I mean.
    Researchers have put living things in centrifuges, and they can survive well if they are tiny bacteria, etc., but there's no reason you can't get insects and spiders doing just fine.
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    Even, rather famously, raising chickens in 2.5G.

    https://blogs.umass.edu/ndarnton/200...tion-research/

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    Quote Originally Posted by glappkaeft View Post
    Even, rather famously, raising chickens in 2.5G.

    https://blogs.umass.edu/ndarnton/200...tion-research/
    Interesting, I remember reading about similar experiments with rats, described as body-builder like rats, thick muscle bound legs and thick muscles everywhere.

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    I'm more curious about how big a solid planet we could get with roughly or slightly less than 1g surface gravity. A more porous, less dense planet could have massive surface area but there would be a lot of wildly different behaviors geologically.

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    Quote Originally Posted by JCoyote View Post
    I'm more curious about how big a solid planet we could get with roughly or slightly less than 1g surface gravity. A more porous, less dense planet could have massive surface area but there would be a lot of wildly different behaviors geologically.
    Then please start a thread about that. It would be quite off-topic for this one.
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  15. #15
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    Quote Originally Posted by KTevolved365 View Post
    The idea of Super Earths fascinates me. So I wanted to get input on this.
    In a calculator I created a planet with 2 Earth radii a density of 9 g cm/3 equaling 13.1 Earth masses. Now this is huge. I am curious if a massive planet like this can be habitable. How would life operate? Thanks ��
    Sorry, I missed this earlier. I like these sort of questions, even if I can't answer them much better than they have already been answered. But there are some details that we haven't considered yet.
    Using this calculator
    http://web.archive.org/web/201608190...iw/Geosync.htm
    I find that the planet you describe has a gravity of 3.29 gees, and an escape velocity of 28.7 km/s. It should retain both hydrogen and helium with ease; this means that for most formation scenarios the planet would retain a very thick atmosphere, and become either a gas giant or an ice giants (ice giants are Neptune-like worlds, with lots of water/ice inside as well as lots of hydrogen and helium). Note as well that the calculator suggests that a planet with a normal Earth-like composition would be slightly less dense, with a density of 8.2g cm/3. I don't actually know how the person who designed this calculator arrives at this estimate, but as far as I know it is pretty reliable.

    To get such a massive, dense planet you would need a larger iron fraction than Earth, and also you would need to remove almost all the volatiles during the formation process somehow, or maybe remove them artificially sometime later (ice pirates?).

    I would guess the biology on such a world would be very squat, low, and strong. You wouldn't want to fall over on a world like that. According to Robert Freitas and other commentators, the landscape relief on such a world would be low, with apparently gently slopes (but you probably wouldn't want to roll down even a gentle slope on a hi-grav planet). I don't necessarily agree that the oceans would be shallow, though- a big planet like that could have deep oceans with no land (but in order to retain the high density, increasing the depth of the oceans would require that you also increase the size of the iron core to compensate).
    Last edited by eburacum45; 2020-Apr-20 at 11:21 AM.

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