WORLD TYPES
Tiny worlds
Tiny (Ice): These diminutive worlds lack the gravitational pull to retain a significant atmosphere, yet their frigid temperatures allow for the accumulation of rich deposits of water ice and similar frozen volatiles. Internal heat, generated by radioactive deposits or tidal flexing, can melt subsurface ice, creating vast "oceans" of liquid water. Typically, Tiny (Ice) worlds manifest as large moons orbiting gas giant planets. Prime examples in our solar system include Jupiter's moons Callisto and Europa.
Tiny (Rock): Too small to maintain a substantial atmosphere and too warm for extensive ice formations, Tiny (Rock) worlds feature surfaces dominated by exposed rock, adorned with craters. Although some may display volcanic activity in their early histories, they swiftly cool, becoming geologically inert. These worlds may exist as large moons or independent planets. Notable instances in our solar system include Mercury and Earth's Moon.
Tiny (Sulfur): This classification pertains to gas-giant moons experiencing intense volcanic activity. Tiny (Sulfur) worlds undergo significant tidal flexing during their orbits, influenced by the gravitational forces of the gas giant and other large moons. This flexing generates interior heat, fostering volcanism. Most released volatile substances escape into space, leaving sulfur and sulfur compounds concentrated on the surface. These worlds pose potential hazards for visitors. An exemplar in our solar system is Jupiter's moon Io.
Small worlds
Small (Hadean): Encompassing worlds with sufficient size to retain gaseous nitrogen, Small (Hadean) worlds are marked by extreme cold that causes their nitrogen atmosphere to freeze on the surface. Typically found as gas giant moons on the outer fringes of a star system, no examples of this type exist in our solar system.
Small (Ice): Possessing enough size to maintain an atmosphere, primarily composed of nitrogen and a mix of more complex compounds, Small (Ice) worlds are characterized by their cold temperatures, harboring abundant water ice and other frozen volatiles. Some may even host liquid "oceans" containing unconventional substances like hydrocarbons. Predominantly, these worlds are large moons orbiting gas giant planets, with Saturn's moon Titan serving as the sole example in our solar system.
Small (Rock): Large enough to retain a thin atmosphere, Small (Rock) worlds lack the mass to hold water vapor and are too warm for surface water to remain frozen. Consequently, any original water content has escaped to space, potentially leaving behind buried deposits of water ice. Mars stands as the lone example of a Small (Rock) world in our solar system.
Standard worlds
Standard (Hadean): Comparable to Small (Hadean) worlds, Standard (Hadean) worlds possess the potential for an extensive atmosphere, yet their extreme cold results in the freezing of most volatile compounds. Typically, found as the largest moons of gas giants on the outskirts of a star system, Neptune's moon Triton is the sole example of a Standard (Hadean) world in our solar system.
Standard (Ammonia): These worlds are large enough to maintain a thick atmosphere containing water and other light volatile compounds. However, their frigid conditions lead to perpetual freezing of pure water, rendering them inhospitable for Earth-like life. Instead, their atmosphere is predominantly composed of ammonia and methane, with liquid ammonia oceans. Ammonia-based life is a possibility on such worlds, but they are rare, typically found near cool red dwarf stars. No examples exist in our solar system, although Uranus and Neptune share some similarities.
Standard (Ice): Possessing a thick atmosphere and abundant water, Standard (Ice) worlds are so cold that most of the water is frozen, covering the rocky surface in a thick layer of ice. Photosynthetic life is scarce or nonexistent, leading to an atmosphere with minimal or no free oxygen. No examples of Standard (Ice) worlds exist in our solar system.
Standard (Ocean): With a thick atmosphere, abundant water, and surface temperatures allowing for liquid-water oceans, Standard (Ocean) worlds lack photosynthetic organisms, either because they haven't evolved or have become extinct. Consequently, their atmospheres contain little or no free oxygen. No examples of this world type are found in our solar system, although Earth fell into this category a billion years ago.
Standard (Garden): Large enough to retain a thick atmosphere, plentiful water for oceans, and a surface climate suitable for human comfort, Standard (Garden) worlds host extensive life, including photosynthetic organisms maintaining free oxygen. Earth is the sole example of a Standard (Garden) world in our solar system.
Standard (Greenhouse): Large enough for a thick atmosphere and abundant water, Standard (Greenhouse) worlds became too warm to support a habitable environment. Experiencing a runaway greenhouse effect, they have extremely hostile surface conditions, with unbreathable, furnace-hot air. Venus, a dry greenhouse planet, is the sole example in our solar system.
Standard (Chthonian): Potentially large enough for a thick atmosphere, Standard (Chthonian) worlds orbit so close to their primary star that stellar winds strip away most volatiles. They may retain a tenuous atmosphere, likely composed of vaporized metals rather than substances conducive to human life. No examples of Standard (Chthonian) worlds exist in our solar system.
Large worlds
Large (Ammonia): Closely resembling the Standard (Ammonia) class, Large (Ammonia) worlds are larger and likely contain a significant amount of helium or hydrogen gas in their atmospheres.
Large (Ice): Similar to the Standard (Ice) class but on a larger scale, Large (Ice) worlds are likely to have substantial amounts of helium or hydrogen gas in their atmospheres.
Large (Ocean): Resembling Standard (Ocean) worlds, Large (Ocean) types feature a thick atmosphere, abundant water, and temperatures conducive to liquid-water oceans. However, their atmospheres are very thick and primarily composed of helium.
Large (Garden): Bearing similarity to the Standard (Garden) type, Large (Garden) worlds have very thick atmospheres rich in noble gases such as helium or neon. These worlds have the potential to support human life.
Large (Greenhouse): Like the Standard (Greenhouse) world, Large (Greenhouse) types have undergone a runaway greenhouse effect, resulting in an extremely dense and furnace-hot atmosphere. Whether or not there are oceans of liquid water, trapped by intense atmospheric pressure, can be defined in a case-by-case basis.
Large (Chthonian): These worlds would typically be large enough to retain a thick atmosphere. However, either their atmosphere has already been stripped away by their primary stars, or they are losing it at a rapid rate, forming a long streamer of gases that peels off into space.
Special worlds
Special (Asteroid Belt): This distinctive "world" comprises a zone or belt of small stony bodies, known as asteroids or planetoids. These celestial bodies may house valuable metals, organic compounds, or even frozen volatiles. While widely dispersed in space, the asteroid belt can consist of numerous planetoids. If settled, inhabitants often reside in artificial habitats floating freely in space or constructed inside the belt's largest planetoids. Inhabited asteroid belts frequently serve as mining or industrial centers. Our own solar system features a significant asteroid belt between Mars and Jupiter.
Special (Gas Giant): Resembling Jupiter-like planets, Gas Giant worlds can be considerably larger than even Large-class worlds, featuring massive atmospheres dominated by hydrogen and helium. Without a solid surface, these worlds are inhospitable for life, even in the upper reaches of the atmosphere. Typically, gas giant worlds are rarely visited and never landed upon, but their atmospheres can serve as valuable sources of hydrogen fuel and other resources. Of particular interest are their extensive systems of moons, many of which are viable worlds in their own right. Most star systems are likely to include gas giant worlds. In our solar system, Jupiter, Saturn, Uranus, and Neptune are examples of gas giant worlds.
RANDOM WORLD TYPES
For the main world in a stellar system, roll 2d6 twice and check the following tables:
Roll 1 | World category
|
4 or less | Hostile
|
5 - 10 | Barren
|
11 - 12 | Garden |
Roll 2 | Hostile | Barren | Garden
|
2 | Standard (Chthonian) | Small (Hadean) | Standard (Garden)
|
3 | Standard (Greenhouse) | Small (Ice) | Standard (Garden)
|
4 | Standard (Greenhouse) | Tiny (Rock) | Standard (Garden)
|
5 | Tiny (Sulfur) | Tiny (Rock) | Standard (Garden)
|
6 | Tiny (Sulfur) | Special (Asteroid belt) | Standard (Garden)
|
7 | Standard (Ammonia) | Small (Rock) | Standard (Garden)
|
8 | Standard (Ammonia) | Standard (Ice) | Standard (Garden)
|
9 | Large (Ammonia) | Standard (Ocean) | Standard (Garden)
|
10 | Large (Ammonia) | Standard (Hadean) | Standard (Garden)
|
11 | Large (Greenhouse) | Large (Ocean) | Standard (Garden)
|
12 | Large (Chthonian) | Large (Ice) | Large (Garden) |