- It represents the mixture of gases and other elements that may be present on a sufficiently sized world or moon.
- Varying types of atmospheres require the use of protective clothing or masks. 
- Very small worlds, planetoids, asteroids, and other small objects almost never have an atmosphere unless artificially modified using advanced technology.
- 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.
- 1 Description / Specifications
- 2 History & Background / Dossier
- 3 References and Contributors
Description / Specifications
Few worlds will be found where a single chemical makes up the entire atmosphere. Most atmospheres have a complex gas mix which will include a variety of specific elements, 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 around us. Three times as much is nitrogen (N2), plus a few trace elements such as argon. These inert gases are not usually required by animal at 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. 
Basic Atmosphere Types
NOTE: They are listed in order of pressure and density.
Expanded Basic Atmosphere Types
Combinations of the below atmospheres may exist and are not comprehensively listed:
- Corrosive Atmosphere
- Dense Atmosphere
- Ellipsoid Atmosphere
- Exotic Atmosphere
- High Pressure Atmosphere
- High Temperature Atmosphere
- Insidious Atmosphere
- Low Pressure Atmosphere
- Low Temperature Atmosphere
- Standard Atmosphere (Tolerable pressure, temperature, constituent gases, etc. for conventional lifeforms)
- Tainted Atmosphere
- Thin Atmosphere
- Trace Atmosphere
- Vacuum (Interstellar Medium)
- Very Thin Atmosphere
NOTE: They are listed in Anglic alphabetical order.
World Atmosphere Classification Codes Table
As a generality, small worlds are unable to maintain a sufficient gravity to maintain an atmosphere and tend to have thinner 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 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 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 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 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. The Ellipsoid World is large and massive, with a thin atmosphere which settles to the lowest levels of the terrain. The atmosphere is unbreathable 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 4, 5, 6, 7, 8, and 9: Thin, standard, and dense atmosphere are breathable without assistance unless tainted.
- Codes A, B, C, D, E, and F: 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 2 to 12 hours.
- Codes D, E, and F: represent "Unusual Atmospheres" with special conditions such as Ellipsoid Atmospheres.
History & Background / Dossier
All industrial societies must 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 of TL:10-12 or greater. The UWP is one of the external expressions of those expectations about atmospheric understandings within Charted Space.
No information yet available.
- Air Tanks
- Atmosphere Tester
- Atmospheric Survival Suit
- Ball, Rescue
- Base, Advanced 
- Battle Dress
- Beacon, Emergency
- Body Pressure Suit
- Cabin, Prefabricated
- Combat Environment Suit
- Combination Filter Mask-Respirator 
- Extended Life Support Sytem 
- Filter Mask 
- Filter Respirator Combination
- Filter Suit
- Gauge, Depth
- Gauge, Tank Pressure
- Hazard Suit
- Hostile Environment Suit
- Locator, Inertial
- Mask, Face
- Mask, Filter
- Mask, Protective
- Oxygen Rebreather
- Oxygen Tanks 
- Pre-Fabricated Cabin 
- Respirator 
- "Sniffer" Bioscanner
- Suit Air Conditioner
- Suit, Protective 
- Suit, Protective, Heavy
- Survival Bubble
- Tent, Pressure 
- Vacc Suit  
References and Contributors
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- Marc Miller. Worlds and Adventures (Game Designers Workshop, 1977), 5.
- J. Andrew Keith. Exotic Atmospheres (Game Designers Workshop, 1983), 1-16. (Special Supplement 2 from the periodical Journal of the Travellers' Aid Society 17)
- Marc Miller. Referee's Manual (Game Designers Workshop, 1987), 22.
- 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.
- Jon F. Zeigler. First In (Steve Jackson Games, 1999), 69-70,72.
- Paul Drye, Loren Wiseman, Jon F. Zeigler. Interstellar Wars (Steve Jackson Games, 2006), 125-6.
- Gareth Hanrahan. Mongoose Traveller Main Rulebook (Mongoose Publishing, 2008), TBD.
- Marc Miller. T5 Core Rules (Far Future Enterprises, 2013), 409.
- Paul Elliott. The Universal World Profile (Zozer Games, 2016), TBD.
- Traveller Wiki Editorial Team
- Author & Contributor: Lord (Marquis) and Master Scout Emeritus Adie Alegoric Stewart of the IISS
- Author & Contributor: Jonathan Sherlock
- Author & Contributor: Lord (Marquis) and Master of Sophontology Maksim-Smelchak of the Ministry of Science
- Marc Miller. Worlds and Adventures (Game Designers Workshop, 1977), 7.
- J. Andrew Keith. Exotic Atmospheres (Game Designers Workshop, 1983), 3-4.
- Paul Elliott. The Universal World Profile (Zozer Games, 2016), 14.
- Gareth Hanrahan. Mongoose Traveller Main Rulebook (Mongoose Publishing, 2008), 170.
- Gareth Hanrahan. Mongoose Traveller Main Rulebook (Mongoose Publishing, 2008), 170.
- Marc Miller. Worlds and Adventures (Game Designers Workshop, 1977), 9.
- Marc Miller. Worlds and Adventures (Game Designers Workshop, 1977), 17.
- Jim Cunningham. High Passage 3 (FASA, 1982), 28.
- Marc Miller. Twilight's Peak (Game Designers Workshop, 1980), 5.