Atmosphere

The Atmosphere Code is the UWP code to represent the mixture of gases constituting an an atmosphere encountered on a world or moon. Some types of atmospheres require the use of protective clothing or masks. The code shows the requirements for using protective gear on the world. The Atmospheric Code is a standard Metric.

Description (Specifications)

Atmospheres have a mix of different gases, some in great amounts, while others are barely detectable. Atmospheric mixes include active and inert gases. On Earth, oxygen (02) is active, but forms less than 25% of the total atmosphere. Three times as much is nitrogen (N2), plus a few trace elements such as argon. These inert gases are not usually required by animal or plant life, and take no part in the chemical reactions essential for life (except for nitrogen, a special case). They are, nonetheless, part of the atmosphere. In this AAB article, when we refer to a specific gas such as methane making up an atmosphere, we are referring to the active element, which may make up only a fraction of the total atmospheric mix.

World Atmosphere Classification Codes Table

As a generality, small worlds have insufficient gravity to maintain an atmosphere and tend to have thin or trace atmospheres while larger worlds grow increasingly dense. Corrosive and insidious worlds tend to be at extreme ends of the tolerable temperature spectrum.

Atmospheric Code Descriptions
Symbol	Code	Specific Description	General Description	Pressure (Atm)	Remarks
	0	Vacuum	Vacuum	< 0.001	Vacuum requires a vacc suit. The atmosphere has a pressure of less than 0.001 atmospheres, which requires the use of a vacc suit.
	1	Trace	Vacuum	0.001-0.09	The atmosphere has a pressure of less than 0.1 atmospheres, which requires the use of a vacc suit.
	2	Very Thin / Tainted	Vacuum	0.10-0.42	Very Thin tainted requires a filter respirator combination
	3	Very Thin	Vacuum	0.10-0.42	Very Thin requires a respirator. The atmosphere has a pressure of 0.1 to 0.42 atmospheres, which requires the use of a respirator to ensure sufficient oxygen.
	4	Thin / Tainted	Thin	0.43-0.70	Tainted requires a filter mask. The atmosphere contains an unusual taint such as such as disease, a hazardous gas mix, pollutants, or sulfur compounds which requires the use of a filter mask.
	5	Thin	Thin	0.43-0.70	Shirtsleeve World: No survival gear required. The atmosphere has a pressure of 0 43 to 0.70 atmospheres. The atmosphere is a standard oxygen/nitrogen mix, which is breathable without assistance.
	6	Standard	Standard	0.71-1.49	Shirtsleeve World: No survival gear required. The atmosphere has a pressure of 0.71 to 1.49 atmospheres. The atmosphere is a standard oxygen/nitrogen mix, which is breathable without assistance.
	7	Standard / Tainted	Standard	0.71-1.49	Tainted requires a filter mask.
	8	Dense	Dense	1.50-2.49	Shirtsleeve World: No survival gear required. The atmosphere has a pressure of 1.50 to 2.49 atmospheres The atmosphere is a standard oxygen/nitrogen mix, which is breathable without assistance.
	9	Dense / Tainted	Dense	1.50-2.49	Tainted requires a filter mask.
	A (10)	Exotic	Exotic , Conventional	varies	An unusual gas mix which requires the use of oxygen tanks, but protective suits are not needed.
	B (11)	Corrosive	Exotic , Conventional	varies	A concentrated gas mix or unusual temperature creates a corrosive environment, which requires the use of a Hostile environment suit or vacc suit.
	C (12)	Insidious	Exotic, Conventional	varies	The atmosphere is similar to a corrosive atmosphere, but extreme conditions cause the corrosive effects to defeat any protective measures in 2 to 12 hours.
	D (13)	Dense, high	Exotic, Unusual	2.5 or greater	Typically no survival gear required under many conditions. Pressure at or below sea level is too great to support life but is breathable at higher altitudes.
	E (14) †	Ellipsoid †	Exotic, Unusual	0.5 or less	Typically no survival gear required under many conditions. The world’s surface is ellipsoidal, not spherical. Because the atmosphere remains spherical, surface atmospheric pressure ranges from very high at the middle to very low at the ends. Breathable bands may exist at some point within the range of pressure.
	F (15) †	Thin, low †	Exotic, Unusual	varies	Typically no survival gear required under some conditions. This world is large and massive, with a thin atmosphere which settles to the lowest levels of the terrain. The atmosphere is un-breathable at most altitudes except the very low ones (…as in depressions or deep valleys).

^† - NOTE: In MgT and T5, Atm type E is "Thin, Low", and Atm type F is "Unusual", which includes (but is not limited to) Ellipsoidal atmospheres.

Protective Measures Based on Atmosphere

The various atmosphere types require specific personal equipment for survival and protection.

Codes 0 and 1

No atmosphere and trace atmosphere require use of a vacc suit and associated support equipment.

Codes 2, 4, 7, and 9

Tainted atmospheres require the use of specialized filter masks.

Codes 2 and 3

Very thin atmospheres require the use of compressors to insure sufficient oxygen to breathe. The tainted very thin atmosphere requires a combination respirator/filter mask for survival.

Codes 5, 6, 8

Thin, standard, and dense atmosphere are breathable without assistance.

Codes A

Exotic atmospheres require the use of oxygen tanks, but protective suits are not usually required unless corrosive or insidious.

Code B

Corrosive atmospheres require the use of protective suits or vacc suits.

Code C

Insidious atmospheres are similar to corrosive atmospheres, but will defeat any personal protective measures in two to twelve hours. The only reliable variant for prolonged survival is heavily fortified, reinforced and armored buildings (deep bunkers) and vehicles (Such vehicles were used since TL7 - for example, soviet "Venera" probes/landers - so future materials should definitely do the job).

The strongest variants of powered armor (like Battle Dress, Augmented Battle Dress, Power Armor, Battle Pod, and other armor models) may protect the Sophont, but it wasn't confirmed experimentally - it's unclear if they will wistand the atmosphere, melt in 2 to 12 hours, or melt for longer than Protective Equipment.

Yet, as written in Techno-Environmental Limits, Sophonts of TL10 and higher do manage to somehow live there.

Codes D, E, and F

These represent "Unusual Atmospheres" with special conditions such as Ellipsoid Atmospheres. The worlds are partly covered with a breathable atmosphere. The survival gear required depends upon where you are located.

Basic Atmosphere Types

Combinations of the below atmospheres may exist and are not comprehensively listed:

1. Corrosive Atmosphere
2. Dense Atmosphere
3. Ellipsoid Atmosphere
4. Exotic Atmosphere
5. High Pressure Atmosphere
6. High Temperature Atmosphere
7. Insidious Atmosphere
8. Low Pressure Atmosphere
9. Low Temperature Atmosphere
10. Standard Atmosphere (Tolerable pressure, temperature, constituent gases, etc. for conventional lifeforms)
11. Tainted Atmosphere
12. Thin Atmosphere
13. Trace Atmosphere
14. Unusual Atmosphere
15. Vacuum (Interstellar Medium)
16. Very Thin Atmosphere

UWP & Atmospheres

The third digit in the UWP identifies the type of atmosphere that the world has. As a rule, only larger worlds have a gravitational field large enough to hold on to an atmosphere, but there certainly are exceptions. An atmosphere is essentially a layer of gas or gasses that cloak the surface of the planet and there are a number of reasons why a world may or may not be lucky enough to have one. As we have already mentioned, a big world has the muscle to keep its atmosphere and the bigger the world, in all likelihood the denser (...or thicker) the atmosphere will be. Conversely, moons and small planets with relatively low surface gravities will generally have only trace atmospheres, if they have anything at all.

Other factors also come into play. A world sitting close to the main star might have its atmosphere stripped away by the destructive energy of the star's solar wind sweeping past. The only chance a planet has of retaining its layer of gasses in this situation, is if it also benefits from a molten core that is producing a protective magnetosphere. Compare the Earth, whose atmosphere is shielded by its magnetosphere, with Mars. The red planet has a trace or very thin atmosphere that was considerably thicker in ancient times, but as the planet cooled it first lost its magnetosphere and then its atmosphere.

Yet there are exceptions; in the depths of the solar system, the moon Titan orbits the ringed planet Saturn. Titan is cold, far from the sun and seismically inactive. It has no magnetosphere and with a surface gravity of only 0.14 G should not be able to retain an atmosphere - yet it has a dense atmosphere that is 1.45 times thicker than that of Earth's. Ganymede and Callisto, comparable-sized moons of Jupiter, are of a similar composition but do not have atmospheres. One theory suggests that Titan, being farther from the sun than the moons of Jupiter, was colder during its formation. Gasses were trapped in the ice at those low temperatures and later made their way into Titan's atmosphere.

History & Background (Dossier)

All industrial societies gain an expanded understanding of atmospheres, air pressure, atmospheric constituents, gas behavior, industrial pollutants, and other factors in order to build a successful, modern interstellar starfaring society.

Tent Worlds are an example of a world ordinarily too small to contain an atmosphere, but artificially and technologically modified to possess an atmosphere using paraterraforming.

Techno-Environmental Limits

The typical sophont species needs to invent various kinds of protective equipment in order to colonize atmospheres to which it is not native.

Techno-Environmental Limits

Atmosphere (Nomenclature) Code	Minimum TL	Remarks
5, 6 or 8	TL-0	No survival equipment required.
4, 7 or 9	TL-3	Tainted atmospheres require filters.
2 or 3	TL-5	Very thin atmospheres require compressors.
13 (D) or 14 (E)	TL-5	Unusual atmospheres require a variety of protective equipment.
0 or 1	TL-8	Trace or vacuum atmospheres require a vacc suit and oxygen tanks.
10 (A)	TL-8	Unbreathable atmospheres require oxygen tanks.
15 (F)	TL-8	Unusual atmospheres such as ellipsoids require survival equipment under selected conditions.
11 (B)	TL-9	Corrosive atmospheres require a variety of capable protective equipment.
12 (C)	TL-10	Insidious atmospheres require a variety of heavy-duty protective equipment.

See also

Atmosphere equipment

• Advanced Base
• Atmosphere Tester
• Atmospheric Survival Suit
• Bioscanner
• Body Pressure Suit
• Combat Environment Suit
• Compressor
• Filter Mask
• Filter Suit
• Hazard Suit
• Hostile Environment Suit
• Oxygen Mask
• Oxygen Rebreather
• Oxygen Tank
• Pressure Tent
• Protective Suit
• Rescue Ball
• Respirator
• Tank Pressure Gauge
• Vacc Suit

Universal world profile

§ == ( Please refer to the following AAB Library Data for more information: ) == §

• Main world
• Hex Number
• Universal World Profile
  • Starport (Sp)
  • Planetary Size (S)
  • Atmosphere (A)
  • Hydrosphere (H)
  • Population (P)
  • Government (G)
  • Law Level (L)
  • Tech Level (TL)
• Trade classification & Sophont Codes
• Importance Extension (Ix)
• Economic Extension (Ex)
• Cultural Extension (Cx)
• Nobility
• Bases
• Travel Zone
• PBG - Population, Belts, Giants
  • P: Population Multiplier
  • B: Belts
  • G: Gas Giants
• Worlds
• Allegiance Code
• Stellar Data
• COG Sequence
  • C: Climate
  • O: Orbit
  • G: Gravity

References & Contributors (Sources)

This list of sources was used by the Traveller Wiki Editorial Team and individual contributors to compose this article. Copyrighted material is used under license from Far Future Enterprises or by permission of the author. The page history lists all of the contributions.

• Marc Miller. Worlds and Adventures (Game Designers Workshop, 1977), 5, 9, 17, 19.
• J. Andrew Keith. Exotic Atmospheres (Game Designers Workshop, 1983), 1-16.
• Joe Fugate. Grand Survey (Digest Group Publications, 1986), 19, 27-28, 34-35, 45.
• Marc Miller. Referee's Manual (Game Designers Workshop, 1987), 22.
• Geir Lanesskog. World Builder's Handbook (Mongoose Publishing, 2023), 64-68.Joe Fugate, J. Andrew Keith, Gary L. Thomas. World Builder's Handbook (Digest Group Publications, 1989), 64-68.
• Terrance McInnes, Dave Nilsen. World Tamer's Handbook (Game Designers Workshop, 1994), 11-17, 84, 90-91.
• Jon F. Zeigler. First In (Steve Jackson Games, 1999), 67-73.
• Robert O'Connor, Atmospheres (Freelance Traveller 2003)
• Paul Drye, Loren Wiseman, Jon F. Zeigler. Interstellar Wars (Steve Jackson Games, 2006), 125-6.
• Gareth Hanrahan. Core Rulebook (Mongoose Publishing, 2008), 41, 137, 170-171, 179.
• Marc Miller. T5 Core Rules (Far Future Enterprises, 2013), 409.
• Paul Elliott. The Universal World Profile (Zozer Games, 2016), 13-18.
• Matthew Sprange. Core Rule Book (Mongoose Publishing, 2016), 217-218.
• Author & Contributor: Lord (Marquis) Jonathan Sherlock
• Author & Contributor: Lord (Marquis) and Master Scout Emeritus Adie Alegoric Stewart of the IISS
• Contributor: Lord (Marquis) and Master of Sophontology Maksim-Smelchak of the Ministry of Science