ATM C POP A = resort planet ?

[captainjack23]

So, one of the more persistent criticisms of PlanGen in Traveller is the old "overpopulated hellhole" canard. Specifically, that one can generate Huge populations on profoundly unihabitable planets. Specifically, Venus (ATM B or C, depending) with 10,000,000,000 inhabitants. Orbital habitats don't seem to be a good enough explanation: they technically "aren't on the planet" for serious rules lawyers, and are rather fragile compared to surface based habitats. However, some serious science thought has been put into exactly this issue -and suggest that Venus may actually be the best bet for extraterran settlement - and could support massive poulations. How ?

http://ntrs.nasa.gov/archive/nasa/casi.ntrs.nasa.gov/20030022668_2003025525.pdf

TLR version, at 50Km altitude, conditions are 1psi, temp 0-30c , good abundance of basic earth life elements : (C, H2, O2, Ni )with lots of solar power opportunities. The basic atmos is unbreathable, but Normal Breathing air is a lifting gas ! Build a huge zeppelin protected against the sulfuric acid atmospheric component (easy, really), and live inside.

Cool, huh ?

The linked paper is actually 7 years old at this point: I'm mildly embarassed that we didn't find this in the playtest discussions about habitable worlds. Quite a bit of opinionizing could have been avoided...perhaps.:mrgreen:

Now, if I can just get some real numbers on the other issue - how long (in actual years) a small world can hold a standard atmosphere ?


Some good fiction led me to this ("Clever Mongoose", I think, and no relation to the present host of this site: a ripping SF yarn with floating cities, tech zombies,conspiracies, and alien invasion all with a steampunk sensibility and a high tech background))

 

[kristof65]

Very interesting article - everything he says makes perfect sense. Here I was thinking Mars was our best bet, and yet after reading that article he's got me convinced Venus is the way to go for several reasons.

I guess the real problem is thinking that we have to inhabit the surface of a planet.

 

[Colin]

The Venus Planet Sourcebook for Jovian Chronicles had these, along with surface arcologies and orbital habitats.

(disclaimer: Yes, I was a contributing author. But it's not like I get royalties or anything)

 

[BP]

Now, if I can just get some real numbers on the other issue - how long (in actual years) a small world can hold a standard atmosphere ?

My first question is - why? This is a game of fiction - but, I know were you are coming from in regards to people's 'suspenders of disbelief'...

There is, of course, no true answer without making the system closed - i.e. science is constantly abused to answer questions about 'possibilities' (more typically, impossibilities) without defined criteria. In the case of a small world that 'answer' is dependent on numerous factors - notably gravity (density and size). But also heat (internally and environmentally), solar radiation and solar wind (how exotic a solar system), out-gassing (is the planet replenishing the atmo), hydrographics (effects latent heat among other things) and related abledo. Also, altitude ranges of the standard atmo is relevant (the stratosphere, for example, is not a standard atmo). And furthermore, whether that atmo is being replenished (or stripped) by another gravitational body (in just the right conditions, another mass may be pulling in ingredients to the local region which can be attracted to - or even simply collide with the small body).

More exotic upper atmo or crustal chemical and systemic processes could also be releasing/retaining/recycling the atmo.

 

[rinku]

That definitely opens my eyes!

 

[captainjack23]

Now, if I can just get some real numbers on the other issue - how long (in actual years) a small world can hold a standard atmosphere ?

My first question is - why? This is a game of fiction - but, I know were you are coming from in regards to people's 'suspenders of disbelief'...

There is, of course, no true answer without making the system closed - i.e. science is constantly abused to answer questions about 'possibilities' (more typically, impossibilities) without defined criteria. In the case of a small world that 'answer' is dependent on numerous factors - notably gravity (density and size). But also heat (internally and environmentally), solar radiation and solar wind (how exotic a solar system), out-gassing (is the planet replenishing the atmo), hydrographics (effects latent heat among other things) and related abledo. Also, altitude ranges of the standard atmo is relevant (the stratosphere, for example, is not a standard atmo). And furthermore, whether that atmo is being replenished (or stripped) by another gravitational body (in just the right conditions, another mass may be pulling in ingredients to the local region which can be attracted to - or even simply collide with the small body).

More exotic upper atmo or crustal chemical and systemic processes could also be releasing/retaining/recycling the atmo.

Yeah, its about those suspenders.... :wink:

Look, here's the deal: when one rolls up one of the odd planets say, size 2 ATM 6 one option one has in the OTU is to assume it was terraformed by (all together now) the ancients.

Putting aside the desirability of such a trope, my question boils down to this: If one is able to add a deep atmosphere to such a a planet, how long will it last ? I'm familiar with most of the variables above, and with Janes Escape and the general relationship between gas activity and escape velocity and temperature.

Here is a specific version of my question:
Assume a size 2 or 3 planet in the habitable zone of a G0V star (such that it is essentially earth normal ) has an oxygen/nitrogen atmosphere equal in pressure at sealevel to earths added to it by artificial means. How long will it last before it is (in traveller terms) a trace or vac atmosphere ? More specifically: will it last 300,000 years ? and how much will be lost in that time ?

 

[far-trader]

Not sure about the duration of the atmosphere dependent solely on gravity holding it but I do recall a theory that Mars lost its atmosphere due more to being geologically dead enough that it's magnetic field was too weak (or non-existent) to divert the solar wind and that is what stripped it off, not a lack of gravity. So you might have to look at more than just size, though size may be a good indicator of molten core and magnetic field strength too.

If Earth lacked the dynamic core it has that produces our strong magnetic field we too would have long ago lost all our atmosphere as well, iirc. Of course there's the other benefits that go with keeping a lot of the radiation going around us instead of through us as well.

 

[BP]

No model or theory of atmos has consistently lasted even our as yet limited actual exploration of our own solar system. Solar bodies expected to have no atmo have turned out to have trace ones, others predicted to be in reasonable temp ranges are infernos, others, inexplicably, have no atmo, etc.

Questions about how long an atmo will last are intractable at this point. Sure, models involving over-simplified assumptions in a closed system can be created - but their results are basically a SWAG at the end of the day. Generally these types of theories fail in some definable ways upon exposure to reality.

As to using 'modern science' to answer your specific question - sorry, you have invalidated it. If you are familiar with the variables you would note that you have introduced a significant unknown set with the 'added to it by artificial means'. The 'means' will affect something else - like assumed gravity.

Nobody has the answer to your specific questions - and no one can - as not enough variables have been defined. Furthermore, today, modern science cannot even tell you what all those variables should be!

Since your goal is, obviously, to have a given planet, with a given atmo after a given time - your question should reflect more how (under what conditions) that could happen. This is a more tractable problem.

 

[captainjack23]

No model or theory of atmos has consistently lasted even our as yet limited actual exploration of our own solar system. Solar bodies expected to have no atmo have turned out to have trace ones, others predicted to be in reasonable temp ranges are infernos, others, inexplicably, have no atmo, etc.Since your goal is, obviously, to have a given planet, with a given atmo after a given time - your question should reflect more how (under what conditions) that could happen. This is a more tractable problem.

Well, yes; and, this is as much metacuriosity as anything else.
The article on colonizing Venus poked a hole in a big assumption about a widely held flaw in traveller. So, it got me thinking about other "well known" facts.
The OTU is explicitly engineered. The small planet big atmosphere issue is at least implicitly dealt with by invoking terraforming of small worlds by aliens who liked low grav plus an atmosphere.



This is usually poo-pooed as scientifically impossible (trope issues aside) However, I've never seen anything other than a math free assertion that a size 3- planet cannot possibly hold an atmosphere for long enough to have terraforming be an explanation. While I agree that this is the case when considering normal astronomical times , I haven't see it actually supported for a timespan which is oreders of magnitude less than normal evolution. (in this case 300 thousand years, as opposed to 4 billion).

Gas diffuses at a predictable rate in a given temperature; simlarly, gas molecules that move faster than escape velocity will be lost if they are pointing the right direction, and if they don't meet resistance (in the form of other molecules. The first is random, the second dependent on density (both known functions).
There must be some relationship that will account for (at least) rate of gas loss from a planetary body over time, with variables for mass and temp and initial volume of gas, even in very crude terms. Any references ?

And yes, I know I can can just "make it be there for the game", and it probably won't matter one bit to the players. I'm just curious to find out if it has to be implausable.

 

[BP]

This is usually poo-pooed as scientifically impossible (trope issues aside) However, I've never seen anything other than a math free assertion that a size 3- planet cannot possibly hold an atmosphere for long enough to have terraforming be an explanation. While I agree that this is the case when considering normal astronomical times , I haven't see it actually supported for a timespan which is oreders of magnitude less than normal evolution. (in this case 300 thousand years, as opposed to 4 billion).

Actually, aside from simplistic models - there is no evidence that this is a true assertion given the scale of the universe and our extreme lack of actual experience with it... there really are just too many factors and too little information to go on.

And any mathematical model will be so crude as to be sheer speculation.

As to astronomical timescales - the Earth's atmosphere is dynamic (according to common scientific theories based on measured indirect evidence and my memory) - '2 billion' years ago it was quite different than today. Only 'a half billion' years ago was it anything like something we modern mammals could live in! (I put those numbers in quotes because they, like a great many larger numbers in science often have +/- 50% or greater error!)

There must be some relationship that will account for (at least) rate of gas loss from a planetary body over time, with variables for mass and temp and initial volume of gas, even in very crude terms. Any references ?

No - there need not be.

Sorry, I am a great lover of science (both in hobby and professionally), but I would also be quite quick to point out it does not have all the answers! Not even close to having all the questions! That is the fundamental problem with your assumption. [I'll refer you to common definitions of that word...]

Atmospheres, even for 'small planets' are absurdly huge volumes. With variations in surface exposure to changing vacumm densities and solar radiation, plus internal chemical reactions and planetary 'outgassing', variations due to the rotation of the planet, axial tilt and orbital eccentricy, not to mention changing magnetic fields and gravity. And I haven't even gotten to the exotic stuffs yet.

The only (mostly) 'static' variable you mentioned was gravity. The temp will vary by numerous factors, while the pressure will vary by the temp, composition and remaining column mass of the atmo, which will, in turn, vary due to the changing density of atmo. One must also ignore the type of chemical and systemic reactions - i.e. like reducing...

To even come up with a 'crude' formula, one would have to assert a very large number of assumptions. Fine if you want something 'normal' like what our limited experience offers. Utterly useless with regards to what you are looking to achieve IMHO.

I'm just curious to find out if it has to be implausable.

No. Likely less common based solely on our limited knowledge - sure. 'Implausable' is very much a matter of opinion - the only scientific evidence requires additional constraints on the assertions - otherwise it is just 'scientifically-based' opinion.

If one were arguing this point - well, both parties would be being foolish.

Seeking a reasonable mathematical model is very noble - but, probably a bit naive.

(Personally, I love mathematics and models - my own studies, rather dated now to be sure, have gone all the way through QCD. But, there are also limits of usefulness.)

 

[far-trader]

As for reasons other than and possibly more recent than Ancient terraforming istr the theory that much if not all of Earth's current atmosphere is the result of icy cometary impacts being revisited recently. So one good (catastrophic for any recent activity) collision could well seed the atmospheric gasses and after an appropriate cooling down period you have a reasonable, though probably short lived, atmosphere on any sized planet. The comet might even introduce some basic life forms (bacterial) to start a very rudimentary ecosystem, something easily adapted to by colonists to kick start their own bigger imported ecosystem.

 

[BP]

Yep - and one could also place the planet in a debris field (disk) such that its supply is constantly being replenished by smaller objects (less catastrophic).

 

[BP]

Also - for some anecdotal evidence - look up Titan's atmo... and read the history of the different 'theories' especially regards pressure and methane.

Titans probably a size 4~3 on the MGT scale - and the closest to Earth's in terms of Nitrogen (majority) constituent. And methane can be burned to produce CO2 IIRC. Exotic reactions, like CO2 being created by irradiating frozen mixtures of water and carbon dioxide in a vacuum, can easily be used to account for various atmo gases.

BTW: Our most current info on Titan probably comes from Cassini (hehe - my dad built some of the instruments on that craft).

 

[AndrewW]

BTW: Our most current info on Titan probably comes from Cassini (hehe - my dad built some of the instruments on that craft).

Don't forget the contribution of Huygens sacrifice.

 

[Mongoose Pete]

Also - for some anecdotal evidence - look up Titan's atmo... and read the history of the different 'theories' especially regards pressure and methane.

Yep. A 0.15g moon with a genuinely Dense atmosphere. The universe is surprisingly perverse sometimes... :wink:

 

[captainjack23]

Actually, aside from simplistic models - there is no evidence that this is a true assertion given the scale of the universe and our extreme lack of actual experience with it... there really are just too many factors and too little information to go on.

And any mathematical model will be so crude as to be sheer speculation.

There must be some relationship that will account for (at least) rate of gas loss from a planetary body over time, with variables for mass and temp and initial volume of gas, even in very crude terms. Any references ?

No - there need not be.

Sorry, I am a great lover of science (both in hobby and professionally), but I would also be quite quick to point out it does not have all the answers! Not even close to having all the questions! That is the fundamental problem with your assumption. [I'll refer you to common definitions of that word...]

Atmospheres, even for 'small planets' are absurdly huge volumes. With variations in surface exposure to changing vacumm densities and solar radiation, plus internal chemical reactions and planetary 'outgassing', variations due to the rotation of the planet, axial tilt and orbital eccentricy, not to mention changing magnetic fields and gravity. And I haven't even gotten to the exotic stuffs yet.

The only (mostly) 'static' variable you mentioned was gravity. The temp will vary by numerous factors, while the pressure will vary by the temp, composition and remaining column mass of the atmo, which will, in turn, vary due to the changing density of atmo. One must also ignore the type of chemical and systemic reactions - i.e. like reducing...

To even come up with a 'crude' formula, one would have to assert a very large number of assumptions. Fine if you want something 'normal' like what our limited experience offers. Utterly useless with regards to what you are looking to achieve IMHO.

I'm just curious to find out if it has to be implausable.

No. Likely less common based solely on our limited knowledge - sure. 'Implausable' is very much a matter of opinion - the only scientific evidence requires additional constraints on the assertions - otherwise it is just 'scientifically-based' opinion.

If one were arguing this point - well, both parties would be being foolish.

Seeking a reasonable mathematical model is very noble - but, probably a bit naive.

(Personally, I love mathematics and models - my own studies, rather dated now to be sure, have gone all the way through QCD. But, there are also limits of usefulness.)

Well, when we had a planetologist here, he sure sounded like there was somthing hard to back it up -problem was, he never gave speciifc numbers, and I don't think he's entertaining traveller questions from me these days...... :wink:

So.....in all politeness, can I ask if you are commenting from a position of actual knowlege of the field ? Or just a good knowlege of science in general.

I understand what you are talking about with regards to limits of science being a scientist myself -just not astroscience- but I'm hard pressed to imagine that something like maxwells laws cannot be applied to estimate retention of atmospheres. If not, well, good enough.

 

[rust]

In my view one of the problems with such questions is that all fields of
science tend to develop some few "standard models", which are then of-
ten misunderstood as true descriptions of the phenomena covered by
them.

As a consequence, if one asks an expert of such a field of science, he is
somewhat likely to explain (or at least to seem to explain) his preferred
current "standard model" as "the truth" without explicitly mentioning that
it is only one of several widely different competing models.

This can become rather confusing, because the experts seem to be so
certain - unless one asks several experts of the same field and realizes
that almost every one of them seems to be certain, but often of some-
thing entirely different and even contradictory.

So, yes, there is a good chance that someone can offer you a formula
and tell you that this is what science does say. Just avoid to ask another
expert, who could offer you a complete different formula ... :lol:

 

[BP]

Rust put things very well (as usual!)

No - this isn't 'specifically' my day job! (And I won't even claim I'm 'good' at science!) I do, however, have an interest and an inside track in this particular area - knowing and having worked with several lead research scientists actively involved in ESA and NASA projects. (My work was not directly related to space research...) My in depth knowledge of Astrophysics is, sadly, rather dated - but my analytical skills are still pretty keen.

Do a little back research you will find that most of our models of atmosphere had to be 'seriously' adjusted to the realities exposed by space probes. And then, re-adjusted when better equipment did their flybys (and the handful of landers, of course). And I'm not talking minor tweaks here either.

Just last year the results from one of the probe satellites my dad worked on turned the prevailing solar wind theory on its head (pun intended)! [I had the low down several months before the findings were officially announced - since the original assumption was that the instruments had failed!]

As a scientist, I hope you can see without too much effort that applying simple ideal gas equations isn't going to even crudely answer your questions about exceptional atmospheres. Not to say calculations can't be done - but this isn't a simple case of mechanical engineering - this is chemistry, biochemistry, solar dynamics, etc. Accounting for changes in atmospheric opacity, Rayleigh scattering, and changes to the equation of state will all be required to handle anything but an oversimplified model.

Now, assuming you are not put off by pages of calculus and dry reading, I do have several (probably dozens) of papers on planetary, exoplanetary and moon atmos (including from a certain planetologist) that I could share when I get a moment (they are not separated among hundreds of other PDFs I have archived). But they provide no simple set of formulas like you desire.

You might want to check out MITs open courseware offerings if you are really interested (I believe there is at least one covering Exoplanets).

There are also several decent physics forums out there - but I'm afraid in this case you will just be tossing fuel on a fire that nobody really has easy answers for...

 

[BP]

Chumbly posted this link in another thread... I think it not only supports my points about the lack of 'knowledge' and pliability of planetary theories - it also supports the idea that 'calculating' lifetime of the atmo is complex or even intractable (without sufficient data). As I mentioned earlier, most of the time an atmo could be 'frozen' (LN2 and LOX - like Pluto/Triton) and the 'thawing' (outgassing/geyser-ing of vaporized N2 with evaporating O2) of this can also (without Ancients) provide for pressure (for a limited time).

[As to one of the 'conclusions' in that article - that higher percentage of highly elliptical orbits may just be due to a greater likelyhood of detection, or a 'local' anomaly.]

 

[rinku]

...all of which pretty much means that 2d6+Size-7 is as good a way of generating atmospheres as any other

From a game point of view, it doesn't matter much if a planet's biosphere has been viable for billions of years or millions, or if it is expected to be uninhabitable in 500,000 years. Just as it's pretty much academic that F type stars age quicker than M types (and in any case, a particular F type may be midway through it's main sequence life, while a particular M type might be on the verge of going nova. The present is what matters most).

2300AD attempted to regulate the atmosphere pretty much by gravity and hab zone alone, and in the end just generated a bunch of boring planets you had to wear a vacc suit to walk around on. Traditional Traveller's approach works better from a gaming point of view.