Create a solar system
Jelly, 78 bytes
“'ĖøÆḳƙ’ḃ7ṣ6+\+3r/ċ€×“½½½½©ÐÇı‘
“ŀỊẋ8ƒ³ẈRɼƈñqẋẏȧɱḌ&lt;ṄỴḳ⁾ÆʋeẒĊ'@ƬØƓƝ}ḟ¬»ỴW€ẋ&quot;ÇẎX

A monadic link accepting an integer (in [4,11]) which returns a list of characters.
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How?
Creates the heat ranges of the planets as a list of lists and counts the occurrences of the input heat in those lists to get a list of zeros and ones representing which planet types are possible, then multiplies by the likelihood numbers of the eight planet types to get the distribution. The distribution is used to repeat the planet type names, and finally a uniform random choice is made.
“'ĖøÆḳƙ’ḃ7ṣ6+\+3r/ċ€×“½½½½©ÐÇı‘ - Link 1, getDistribution: integer
“'ĖøÆḳƙ’                        - base 250 integer = 39824688429662
        ḃ7                      - to bijective-base 7 = [1,1,2,4,7,1,4,4,6,2,2,2,2,1,5,3,3]
          ṣ6                    - split at sixes = [[1,1,2,4,7,1,4,4][2,2,2,2,1,5,3,3]]
             \                  - cumulative reduce with:
            +                   -   addition = [[1,1,2,4,7,1,4,4][3,3,4,6,8,6,7,7]]
              +3                - add three = [[4,4,5,7,10,4,7,7],[6,6,7,9,11,9,10,10]]
                 /              - reduce with:
                r               -   inclusive range = [[4,5,6],[4,5,6],[5,6,7],[7,8,9],[10,11],[4,5,6,7,8,9],[7,8,9,10],[7,8,9,10]]
                  ċ€            - count (input) in €ach e.g. for 5: [1, 1, 1, 0,0, 1, 0, 0]
                     “½½½½©ÐÇı‘ - list of code-page indices        [10,10,10,10,6,15,14,25]
                    ×           - multiply                         [10,10,10, 0,0,15, 0, 0]

“ ... »ỴW€ẋ&quot;ÇẎX - Main link: integer
“ ... »         - compressed string = &quot;Ice\nIce Giant\nGaia class\nDense Atmosphere\nLava\nGas Giant\nIron\nDesert&quot;
       Ỵ        - split at new lines = [&quot;Ice&quot;,&quot;Ice Giant&quot;,&quot;Gaia class&quot;,&quot;Dense Atmosphere&quot;,&quot;Lava&quot;,&quot;Gas Giant&quot;,&quot;Iron&quot;,&quot;Desert&quot;]
        W€      - wrap €ach in a list
            Ç   - call last link (1) as a monad e.g. for 5: [10,10,10,0,0,15,0,0]
           &quot;    - zip with:
          ẋ     -   repeat e.g. for 5:  [[&quot;Ice&quot;,&quot;Ice&quot;,&quot;Ice&quot;,&quot;Ice&quot;,&quot;Ice&quot;,&quot;Ice&quot;,&quot;Ice&quot;,&quot;Ice&quot;,&quot;Ice&quot;,&quot;Ice&quot;],[&quot;Ice Giant&quot;,&quot;Ice Giant&quot;,&quot;Ice Giant&quot;,&quot;Ice Giant&quot;,&quot;Ice Giant&quot;,&quot;Ice Giant&quot;,&quot;Ice Giant&quot;,&quot;Ice Giant&quot;,&quot;Ice Giant&quot;,&quot;Ice Giant&quot;],[&quot;Gaia class&quot;,&quot;Gaia class&quot;,&quot;Gaia class&quot;,&quot;Gaia class&quot;,&quot;Gaia class&quot;,&quot;Gaia class&quot;,&quot;Gaia class&quot;,&quot;Gaia class&quot;,&quot;Gaia class&quot;,&quot;Gaia class&quot;],[&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;]]
             Ẏ  - tighten               [&quot;Ice&quot;,&quot;Ice&quot;,&quot;Ice&quot;,&quot;Ice&quot;,&quot;Ice&quot;,&quot;Ice&quot;,&quot;Ice&quot;,&quot;Ice&quot;,&quot;Ice&quot;,&quot;Ice&quot;,&quot;Ice Giant&quot;,&quot;Ice Giant&quot;,&quot;Ice Giant&quot;,&quot;Ice Giant&quot;,&quot;Ice Giant&quot;,&quot;Ice Giant&quot;,&quot;Ice Giant&quot;,&quot;Ice Giant&quot;,&quot;Ice Giant&quot;,&quot;Ice Giant&quot;,&quot;Gaia class&quot;,&quot;Gaia class&quot;,&quot;Gaia class&quot;,&quot;Gaia class&quot;,&quot;Gaia class&quot;,&quot;Gaia class&quot;,&quot;Gaia class&quot;,&quot;Gaia class&quot;,&quot;Gaia class&quot;,&quot;Gaia class&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;,&quot;Gas Giant&quot;]
              X - a random choice from that list