| If planet has: | the alien would most likely have: |
|---|---|
| thin atmosphere (sound waves don't travel well, little oxygen) | large ears, big lungs, compensate for bad hearing with increased other senses |
| heavy atmosphere (good sound, lots of oxygen) | little ears, small lungs and nostrils |
| lots of gravity (strong pull) | strong skeletal structures, short and squat |
| little gravity (little pull) | light skeletal structures (such as birds, with their hollow bones) |
| very hot | insulation, ways to radiate heat (such as elephants with their big ears) |
| very cold | insulation (such as fur or blubber) |
| strong winds | aerodynamic, possibly sails |
| lots of water | sea creatures (such as fish, algae, sea stars, plankton, sea cucumbers, octopi) |
| little water | efficient storage system (such as cacti, camel) |
| lots of light | reflective (to radiate), shade-covered |
| little light | big eyes, other senses increased to compensate |
| little food source | efficient storage system (fat storage such as elephant seals) |
| only atmosphere, no surface (such as Jovian planets: Jupiter and outwards) | creatures that fly, hover, float or "blow up" (such as a blow fish) |