Rime

A world that never held enough heat to be anything else, or that lost it long ago. The surface is water ice, methane and ammonia in sheets kilometers thick, shot through with crystal where pressure has acted over a long time. Some are geologically active and vent water and ammonia on unmapped cycles. Volatiles are what a Rime is worth, and they lie far from any authority with power to tax them, so the Axiom Combine has fabricators on several that it last checked on more than a decade ago.

Planetary environment

Crossing it

Navigate: DC 12
Forage: DC 10
Notice: DC 8

Foraging means cutting volatiles out of the surface.

Exposure

Extreme Cold

Temperatures below about zero degrees Fahrenheit, or any water near freezing, made worse by wind.

CON save, DC 10, rising by 1 for each hour after the first. End of each hour. One level of exhaustion.
- Cold-weather gear
  
  Proper layers, a sealed suit or a heated shelter removes the save. Wet layers give disadvantage on it instead.
- Immersion
  
  A creature in near-freezing water makes the save each minute instead of each hour, and is Incapacitated at three levels of exhaustion.
- Gear
  
  Unheated power cells lose half their charge, and any check made with bare hands after an hour of exposure has disadvantage.
- Adapted
  
  A creature native to a cold world, or with resistance to cold damage, ignores the save.
Vacuum

No pressure and no air to breathe, with survival measured in rounds.
- Countdown
  
  Without a seal, a creature holds out for a number of rounds equal to its Constitution modifier, minimum 1. At the end of that time its hit points drop to -1, unless they are already lower, and it is dying. It cannot be stabilized or regain hit points until it can breathe.
- Decompressed
  
  Exposure inflicts the Decompressed condition, which a return to pressure does not by itself remove.
- Holding your breath
  
  Holding a breath in vacuum ruptures the lungs. A creature that does so takes 2d6 damage on the first round and gains no benefit from the attempt.
- Sound
  
  Sound does not travel. Verbal spell components, shouted orders and Perception by hearing all fail across open vacuum. Suit comms and touch are the only channels.
- Unfiltered light
  
  Without air to filter it, the star's output arrives unreduced. An hour of unshielded exposure in direct sunlight counts as a failed Contaminated Atmosphere save against radiological dose.
Low Gravity

Gravity below about 0.4g, where a push-off sends a creature farther than expected and stopping takes planning.
- Movement
  
  Ground movement is normal, but any push-off sends the creature farther. A creature that Dashes continues an extra 10 feet in the same direction at the end of its turn unless it spends 5 feet stopping.
- Melee
  
  A melee attack made without an anchor point pushes the attacker 5 feet away from the target after the attack resolves.
- Jumps and falls
  
  Jump distances are tripled and falling damage is halved. A fall of under 40 feet does none.
- Carrying capacity
  
  Carrying capacity is tripled. Mass is unchanged, so anything being carried is as hard to start and stop as it is at normal gravity.
- Mag boots
  
  Magnetic boots or a tether remove every entry above while a ferrous surface is underfoot, at the cost of half movement.

In play

Permanent tracks

There is no weather and no erosion. Survival checks to follow a trail here succeed automatically, including checks to follow the party.
Volatiles

Water and hydrocarbons are available at the surface. A vessel can refuel and resupply indefinitely at the cost of time.
Cryovolcanism

Uncharted vents throw plumes of water and ammonia. A vent field on a Rime freezes the plume before it lands.
Crystal

Long-grown ice refracts light and conducts sound. Light sources are visible at three times their own radius, and Stealth checks that rely on silence have disadvantage on bare ice.
Under the shell

Where tidal heating has kept a liquid ocean under the ice, it is reached through a bore or a vent, and it imposes Crush Pressure instead of cold.

Regions on it

Arctic Permanent ice over land, flat to the horizon, with the ice flowing slowly underneath.
Aurora The rings where a world's magnetic field funnels the star's wind into the upper air.
Frozen Sea Ocean covered by a layer of sea ice that supports weight until it breaks, over water that stays liquid.
Near Space The last of the atmosphere, thin enough to count as vacuum for every purpose except drag.
Subterranean Everything under the surface, with no light, no weather, and a route set by what the rock allows.
Upper Atmosphere The stratosphere and mesosphere, above the weather and below space, with no breathable air and little lift.