The Planet creation guide is to help users create new worlds as well as environments for their species to live in. It may be wise to read this article if you are unfamiliar with the terminology we use on this wiki.
Though we are tempted to believe it, not every planet is going to be exactly like Earth. Of course, Earth can be used as a template, but from there, start thinking about what makes your planet unique. First of all, its geography and positioning in its solar system will make it different from Earth already.
The star type has numerous effects on the planet itself. While G and K stars are similar to our sun, M and F stars are known for their UV radiation. Also, around M stars, planets are tidally locked due to the close distance it must be. For exact numbers on how far a planet should be from a star to be habitable, see the habitable zone page. Earth is 1AU from the sun.
There's also believed to be a galactic habitable zone. Planets closer to the center of the galaxy are more at risk from gamma radiation, while planets further out tend to have less metal rich stars.
The color of the star will also affect the color of plant life. Dimmer stars will mean darker plants.
If a planet has one or more moons, its day/night cycle will be considerably slow. Moons also have numerous effects on the planet itself such as earthquakes and changes in sea level.
If your world is a moon instead, it would most likely orbit a gas giant. The moon will be tidally locked to the gas giant and experience brief periods of total darkness once every month.
A gas giant can also tidally heat up a moon to cause tectonic activity.
Gravity is determined by a planet's density and diameter. Larger planets tend to have higher gravity, while smaller planets tend to have lower gravity.
A planet's gravity will affect the size and shapes of animals. Higher gravity planets tend sport creatures that are short and squat while taller, thinner creatures can be found on low gravity worlds. Earth's gravity is 1G.
High oxygen levels will make wildfires extremely common. A high presence of carbon dioxide will allow plants to grow to large sizes. CO2 levels of 1% or more are considered dangerous. In environments with less than 15% oxygen in the air, flames will be snuffed out.
Planets with atmospheric pressures higher than Earth will have more room in the habitable zone, though less temperature variation on the planet. Organisms in a high pressure environment can grow to enormous sizes. Planets with low atmospheric pressures will have greater temperature variation.
A planet with high atmospheric pressure could be found outside the habitable zone, but still be habitable.
Earth's atmospheric pressure is 1 atm.
Rather than plucking an animal from Earth and placing it on your planet, create an animal that has to adapt to the environment. Alien animals do not have to abide by Earth's standard classifications (i.e. insect, mammal, reptile etc).
For example, a world with a weak magnetic field would require the native life to evolve metallic carapaces to shield them from the radiation, and a species having evolved on a planet orbitting a red dwarf star would need someway to be able to efficiently hide from the sun's regular radiation bursts.
You'll also need a food chain. Energy begins with autotrophs, harvesting energy from the sun (or geothermal vents). The autotrophs are preyed upon by the herbivores, and the carnivores prey upon the herbivores. With each trophic level, energy is lost, so there will be less carnivores than herbivores.
If a planet has a sapient species, then you should heavily focus on them having a well developed brain structure as that is perhaps the main reason why they are sapient in the first place. A sapient species should be highly adaptable.
Carnivorous sapients are believed to be more common than herbivorous sapients. The reason being is that carnivores have to rely more on cunning stealth, while herbivores just have to know how to run. Elephants are a notable creature in that they are one of the most intelligent of herbivores.
Technologically advanced societies will need a way to perform metallurgy, so the development of water-based civilizations will be slow.
- Take advantage of your planet's unique features. It's an alien planet after all, so make use of geographic features or weather patterns not found on Earth.
- Don't make your planet exactly like Earth. While undoubtedly, there's bound to be other Earth-like worlds out there, no two planets are exactly alike.
- Don't forget to make your planet geographically varied. Remember that when we refer to swamp or desert planets, that's not to say they only have one biome.
- Use the List of external tools to determine precise numbers. That way, the numbers make sense.
- Be creative and have fun!