Temperature

Mongoose Traveller uses optional rules to determine a world’s temperature. The approach assumes that worlds are in the habitable zone of their host star and is a dice roll with DMs based on atmosphere. I like to include these optional rules because they give us a lot of (necessary!) information on the world.

The existing rules never made it into the SRD and I don’t feel like having a debate about the copyright status of game rules so I will simply design a new system from scratch.

We’ll be using these temperature categories:

  • Frozen: The world is completely frozen; any water it may possess is ice. If it has an atmosphere it has a very low humidity. Example: Europa, Snowball Earth.
  • Cold: The world is within human habitability range, but uncomfortably cold. It’s an icy world with extensive ice caps, with harsh winters. Nights are usually too cold for humans outside heated shelters. Example: Ice Age, Hoth (Star Wars), Mars (at the lower end of the scale).
  • Temperate: The planet is roughly comparable to Earth.
  • Hot: The planet is uncomfortably warm but still habitable. It has small or no ice caps, and a lot of moisture is contained in the atmosphere. Examples: Tatooine (Star Wars), Barsoom, Dune
  • Roasting: The planet is too hot for human habitation. It has no open oceans or ice caps. Examples: Mercury, Venus (at the upper end).
  • Searing: This world is extremely hot up to a temperature range where its surface may be permanently molten. Still, in a super-tech future there may be ways to colonize such worlds, for example for mining. Example: Kepler-78b.

Generally stating, a vacuum world will have a much wider temperature range than a planet with an atmosphere; an atmosphere also helps a planet retain heat. Worlds closer to the sun will be warmer than those further out. – We probably do not need more detail than this.

The assumption that these planets are the “best” their systems have to offer will come in heavily here. Also, all other things being hypothetically equal, colonists will prefer a cold world over one that is very hot, because heating is easy and cooling is difficult if the ambient temperature is high.

I am also assuming that an N2/O2-Atmosphere requires the world to be habitable in order for life to be present which can refresh atmospheric O2.

Instead of doing a one-dimensional list with a lot of DMs thrown in, I thought a look-up-table may work. Roll 2d6, then cross-reference your atmospheric type:

Vacuum
Traces

V. Thin,
Thin

Standard

Dense

Exotic
Corrosive

Insidious

2

Frozen

Frozen

Frozen

Cold

Frozen

Cold

3

Frozen

Frozen

Cold

Temperate

Frozen

Temperate

4

Cold

Cold

Cold

Temperate

Cold

Temperate

5

Cold

Cold

Temperate

Temperate

Cold

Hot

6

Cold

Cold

Temperate

Temperate

Temperate

Hot

7

Temperate

Temperate

Temperate

Temperate

Temperate

Hot

8

Temperate

Temperate

Temperate

Hot

Hot

Roasting

9

Hot

Temperate

Temperate

Hot

Hot

Roasting

10

Hot

Hot

Hot

Hot

Roasting

Roasting

11

Roasting

Hot

Hot

Roasting

Roasting

Roasting

12

Searing

Roasting

Roasting

Roasting

Searing

Searing

Of course it is not intuitive to infer results from this table; so here is the actual distribution:

tempgraph01

Seems fairly reasonable to me, but it needs playtesting and a sanity check (I am beginning to wish I had a science adviser). Interpretation of the results is left to the GM, but should be easy in most cases. For vacuum worlds, it translates more or less directly to distance from the sun (or other heat-providing body).

For a planet with breathable atmosphere we can probably infer its orbital distance within the habitable zone, but other factors will influence this. For example, a cold Earthlike world can simply be in an ice age or even a Snowball phase. If the taint is a greenhouse gas, then this will affect temperature as well.

Dense atmospheres are better at retaining heat.

For Exotic and corrosive atmospheres, it’s a toss-up (Titan is very cold, Venus is hellishly hot). I find it hard to imagine a really frozen insidious atmosphere world, since I assume this will cause many chemicals to precipitate out of of the atmosphere.

Effect on Hydrographics

The effects of temperature on liquids on a world should be obvious, but before I encode them I need to contemplate what to do about the “liquid water” vs “includes ice caps” conflict in the Hydrographic characteristic.

 

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