Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Calculations for theoretical planet + a little biology

  1. Jun 13, 2018 #1
    So I'm attempting to write a scientifically accurate story and i need some help with the planets characteristics. I have a few things set up already and need some educated guesses and ideas for how the rest will work. So to start with what i have:
    Planet name: Remvale
    Radius:~8370 miles
    Gravity: 8.73 meters/sec
    Atmosphere pressure: 3.7 atmospheres
    Atmosphere composition: haven't decided except for around 34% oxygen
    Surface: 62% water 38% land

    So the questions i have are as follows:
    -Density of planet? It has roughly twice the radius of earth but a lower gravity so it will be much lighter, is the density a realistic mass?
    -Is the atmosphere pressure survivable for an entire human lifespan? If so what is the max pressure for normal human life and what adaptions would be needed?
    -Could humans adapt to live a normal lifespan in such an oxygen rich environment?(sorry this isn't astrophysics but i heard that increased oxygen levels would shorten lifespan)
    -What planetary events could cause a rapid increase in oxygen level? (roughly 20% in almost 1000 years?)
    -Would the increased atmosphere pressure cause any optical effects? (ex. venus atmosphere being impossible to see through)
    -What gas mixtures would be needed for life and temperatures similar to earth's to exist? (just basics like nitrogen oxygen and carbon dioxide)
    -What basic animal types would survive best on this planet? ( out of reptiles, birds, insects, mammals, amphibians, fish, ect.?)

    Sorry, i know this is a lot of questions from a lot of fields. I'm not expecting any one person to try to answer them all, feel free to do as many or as few as you want. Thanks!
  2. jcsd
  3. Jun 13, 2018 #2


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

  4. Jun 13, 2018 #3
    If I did the math correctly, the partial pressure of oxygen there would be around six times of on Earth. And yes, Oxygen is toxic.
    I would say it would be quite bad within hours. (Six bar partial pressure is not even on this graph below.)
    (Graph is from the linked Wiki page)
  5. Jun 13, 2018 #4


    User Avatar
    Science Advisor

    Those numbers require the average density of 2.3 g/cm3*. Which begs the question: what happened to all the metals during the formation of the planet?

    *the relationship is simple: starting with Earth - X times the radius means X times the gravity. Y times the density means Y times the gravity.
    Here you have (roughly) twice the radius and the same gravity, so the density must be 1/2.
  6. Jun 13, 2018 #5


    User Avatar
    Science Advisor
    Homework Helper
    Gold Member

  7. Jun 14, 2018 #6


    User Avatar
    Staff Emeritus
    Science Advisor

    This video, and others on the channel, should help you come up with a realistic planet:

    At 3mins 38secs he goes over something that I think is quite relevant: how the relationship between radius and mass determines what kind of planet you get. If the planet is large and low mass it will have formed as a mini-gas planet. If it's too high mass you get a world covered in incredibly deep water/ice. There is a handy chart drawn from a book (which I think is referenced in one of the videos) that shows the range of conditions necessary for a rocky world.
  8. Jun 14, 2018 #7
    Not really, as other posters explained.
    Pressure probably is, but...
    No. As other posters explained. 1,2 bar partial pressure of oxygen is fatal in a few days.
    Cannot think of any that are this fast.
    Increased Rayleigh scattering and refraction. And the larger radius of planet would contribute to both.
    Other safe components are Ne and He
    All 6 are classes in Earth Cenozoic, and all save one are vertebrates.
    High air density would favour birds.
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted