Don's Planetary Size Hack

[Garnfellow]

Don McKinney developed a very clever hack to adjust planetary Size based on Atmosphere, which avoids implausible UWPs such as a Size 1 world with a standard oxygen-nitrogen atmosphere without changing the world's trade codes. The size adjustment was applied to most sectors reviewed by the T5SS project but never well documented. I did a blog post to document his hack, which I still use on sectors I generate for my own games.

 

[tjoneslo]

https://greatdungeonnorth.blogspot.com/2024/03/adjusting-world-sizes-for-atmosphere.html?m=1 - your link gave me a "not found" error. But that was on my phone. I do like your fix though. Very elegant.

 

[TamsinP]

It seems that the link has somehow been doubled so you get "linklink" which is why it doesn't find it.

 

[Garnfellow]

The link seems to be working now. Not sure what I did, but thanks for the heads up.

 

[Kakistocrat]

Don McKinney developed a very clever hack to adjust planetary Size based on Atmosphere, which avoids implausible UWPs such as a Size 1 world with a standard oxygen-nitrogen atmosphere without changing the world’s trade codes. The size adjustment was applied to most sectors reviewed by the T5SS project but never well documented. I did a blog post to document his hack, which I still use on sectors I generate for my own games.

Thanks for posting that on your blog; I hadn’t seen Don’s hack before. In the case of classic Traveller, do the Sizes before the Atmospheric hack include possible modifications for star type and/or orbit number, per the stellar system generation procedure in Scouts ? (For example, the odds of rolling a particular world Size would vary if its star type is M.)

 

[Garnfellow]

Thanks for posting that on your blog; I hadn’t seen Don’s hack before. In the case of classic Traveller, do the Sizes before the Atmospheric hack include possible modifications for star type and/or orbit number, per the stellar system generation procedure in Scouts ? (For example, the odds of rolling a particular world Size would vary if its star type is M.)

I don't think so. A T5SS review would typically make a pass through the stellar data to tamp down the more gonzo results like white dwarfs with breathable atmosphere mainworlds, supergiants with habitable worlds that produced native sophonts. A common change would be to increase the size of small red giant primaries, so you don't have many primaries smaller than M3 V or M4 V.

 

[Spinward Flow]

I did a blog post to document his hack

Responding (here) to the points raised in your post on your blog.

“A problem with the random generation of worlds in Traveller is that small worlds (where size < 4) … might get an ordinary breathable atmosphere. This is a problem, since the minimum molecular weight retained for a [small] planet shouldn’t allow that.” Basically, small worlds cannot retain most atmospheres over billions of years: the consitituent gases escape the gravitational pull of the planet and dissipate into space.

True ... BUT ... not every world is in a circumstance of "been here for 4 billion years already" during which nothing much happened (after the Late Bombardment phase). My point being that it is perfectly possible that the CURRENT atmospheric conditions on a small world are a TRANSITORY PHENOMENON, rather than some kind of "steady state" that's going to last for billions of years.

It could be something as simple as in the (recent) geologic past of a planet there was a LOT of volcanic outgassing, which gave the planet "too much atmosphere" for its surface gravity and the atmosphere is in the process of being stripped away by solar radiation ... but that process hasn't finished yet. One of those "you're 200 million years into a 500 million year atmospheric loss event" kinds of deals, in which the CURRENT atmospheric conditions are an "anomaly" that will change over time scales that are civilization relevant but not current resident relevant.

Sort of like how Sol will continue to increase in luminosity over the next 500 million years to the point where the water oceans of Terra will start to evaporate into the atmosphere until Terra becomes a runaway greenhouse gas hellworld like Venus that boils off the oceans completely, transforming all that water from liquid to gas/vapor. So EVENTUALLY Terra will become "not exactly habitable" long before Sol enters its Red Giant phase of Helium fusion (and expands the photosphere outwards to engulf Terra's orbit completely, really making the planet "a bad place to try and live, long term") ... but RIGHT NOW it's a pretty hospitable place to live, on a sophont civilization timescale, but not on a geologic/stellar evolution timescale.

The UWP doesn't have to be something that represents the way conditions would need to be for billions of years in an undisturbed equilibrium. The UWP simply has to show what conditions are RIGHT NOW.

Take Dinom/Lanth that was featured in LBB DA2 Across The Bright Face for example.
Because of how Dinom orbits the star and the rotation axis of the world, the atmosphere FREEZES onto the surface during "summer/winter" and sublimates back into being an actual atmosphere during "spring/autumn" cycles, so there is a seasonal cyclical nature to the atmosphere. Since the orbital period is so long (1600 years) you get about 400 years per season "annually" on Dinom. Point being that the UWP for atmosphere on Dinom is "not a constant" but instead varies, but the variation is on a timescale that is so long that it is "daily lived experience irrelevant" so the UWP simply reports CURRENT conditions, not eternal ones.

I therefore submit for your consideration that the "worlds too small CAN'T have breathable atmospheres" problem is only a problem if you're trying to approach the issue from the standpoint of being a "steady state, simplistic planetary evolution" where nothing particularly notable has happened in all of geologic history.

Mars can be an arid dusty wasteland because radiation from Sol has stripped away the atmosphere from the lower Mars gravity ... but if there was a Major Collision™ in the recent geologic past with a substantial icy comet type object of some kind, Mars might receive "a lot more atmosphere" as a result (and even have liquid water on its surface!) ... for a while. It wouldn't be a "permanent" condition that would last billions of years, but if it lasts the next "several hundred to a million years" that's good enough for UWP data results!

In other words, by taking the "small worlds with breathable atmosphere" as being a PROBLEM TO CORRECT rather than as an OPPORTUNITY TO EXPLAIN ... you preclude a lot of potential for "world building" in Traveller writ large.

Even something as simple as a "planet captures rubble moon rich in ices" into an orbit that somehow takes the capture down inside the Roche Limit, causing the captured moon to eventually disintegrate and "rain down onto the surface of the planet" could potentially be the reason why a world that "shouldn't" have a "breathable atmosphere" actually DOES have one ... for a while ... long enough to be relevant to a UWP code when surveyed.

Basically, small worlds cannot retain most atmospheres over billions of years: the consitituent gases escape the gravitational pull of the planet and dissipate into space.

True ... BUT ...
Do we NEED our UWPs to report "eventual steady state conditions" that will exist billions of years from now ... or do we need UWPs to report conditions that prevail RIGHT NOW, which could potentially change in the future?

Spoiler alert: I prefer the latter over the former ... which means that some "anomalous" combinations of UWP codes, such as small worlds with low gravity having relatively thick atmospheres being a "legal" result out of world creation. To me, that just means that the "current" environmental conditions on those worlds is a "temporary" condition, rather than a permanent one.

 

[Spinward Flow]

I wanted to write this blog entry because Don’s nifty size hack was never well publicized and even today folks will occasionally wonder why Traveller Map UWPs don’t line up with the published UWPs from early GDW supplements like The Spinward Marches.

🖐 Guilty as charged.

The size hack makes sense for a more "orderly" Traveller Universe in which planets "have always been this way" (for billions of years) and represents more of a "steady state" approach to world generation ... rather than a "stuff may have happened 'recently' to make current conditions that are not sustainable/permanent" type of understanding.

Contrast that with things we now know (but didn't previously) such as the fact that the Rings around Saturn are NOT a Permanent Feature™ of the Saturn planetary system. They're a (relatively) recent addition ... in terms of the age of the solar system.

While traversing the gap between the rings and planet in September 2017, the Cassini spacecraft detected an equatorial flow of charge-neutral material from the rings to the planet of 4,800–44,000 kg/s. Assuming this influx rate is stable, adding it to the continuous 'ring rain' process implies the rings may be gone in under 100 million years.

Would any of us (as planetary system surveyors) look at the ring system around Saturn and decide that because "it's here now, but it won't last, I'll just leave it out of my UWP report" ...?

Answer: No.
We would include Saturn's Rings in our UWP extended report, because the feature IS HERE NOW ... even if won't be here "always" (and forever).



My point is that not every "characteristic" of a UWP needs to be "long term stable" for billions of years in order to be "valid" as a result. Those characteristics simply need to "current conditions" ... which can potentially be a TEMPORARY state, rather than a permanent one(!), which is currently undergoing some kind of decay and transition (over global time scales, of course). All kinds of planetary history events can cause temporary conditions that are not "long term viable or stable" ... starting with impact events of various types and sources.

 

[tjoneslo]

True ... BUT ...
Do we NEED our UWPs to report "eventual steady state conditions" that will exist billions of years from now ... or do we need UWPs to report conditions that prevail RIGHT NOW, which could potentially change in the future?

I think the good question here what time scale are we considering. You can give the Moon (a size 1 world) an Earth scale density atmosphere. But, as you point out, it won't last. Depending on the source you reference, that time scale could be between 1,000 and 100K years. The other side of that is terraforming efforts. Over a few hundred or 1,000 years you can add air, water, and life forms to a world. So at what point do you update the UWP to reflect the new reality. And if it's going to be changing, how often should it be updated.

 

[Dragoner]

I think the good question here what time scale are we considering. You can give the Moon (a size 1 world) an Earth scale density atmosphere. But, as you point out, it won't last. Depending on the source you reference, that time scale could be between 1,000 and 100K years. The other side of that is terraforming efforts. Over a few hundred or 1,000 years you can add air, water, and life forms to a world. So at what point do you update the UWP to reflect the new reality. And if it's going to be changing, how often should it be updated.

I have explained it this way before, there are other mentions of terraforming, and colonization projects.

 

[Kakistocrat]

Here’s a recasting of Don’s hack into the Scouts stellar system generation procedure, taking the atmospheric DMs into account. This method only affects the atmosphere result; it does not change the generated size of the world or satellite. Each step should be followed until reaching a result on a line with an “END” arrow.

Atmosphere: 2D − 7 + size​

• If world in inner zone, DM −2; if world in outer zone, or satellite in either inner zone or outer zone, DM −4
• If size 2−, then atmosphere 0.
• If size 3+ and habitable zone +2 or greater, then throw 2D without DM:
  • If 12, then atmosphere A.
• If size 3 with DM −4, then throw 2D without DM, rerolling until 9−:
  • Atmosphere is throw − 8.
• If size 3 with DM −2, then throw 2D without DM, rerolling until 7−:
  • Atmosphere is throw − 6.
• If size 3, then throw 2D without DM, rerolling until not 6–8:
  • If 4− or 10+, then atmosphere 0.
  • If 5 or 9, then atmosphere 1.
• If size 4 with DM −4, then throw 2D without DM, rerolling until 10−:
  • Atmosphere is throw − 7.
• If size 4 with DM −2, then throw 2D without DM, rerolling until 8−:
  • Atmosphere is throw − 5.
• If size 4, then throw 2D without DM, rerolling until not 7:
  • If 3− or 11+, then atmosphere 0.
  • If 4 or 10, then atmosphere 1.
  • If 5 or 9, then atmosphere 2.
  • If 6 or 8, then atmosphere 3.
• If size 5+, use atmosphere as rolled.

Atmospheres that are less than 0 become 0.