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Old 11-14-2017, 11:50 AM   #1
acrosome
 
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Default Implications of a terraformed Venus/Triton?

I have got one hell of a series of technical questions for anyone who knows more astrophysics than me, which should be just about anyone who would click on a thread with that title. :)

I'm working on my longstanding on-and-off project for a low-tech campaign setting on a terraformed Venus in the far future after the Fall of Man (TM). Venus has been spun up to have a 24-hour day with a 20 degree axial tilt, and moved further out from the sun to have a 366-day year; even months have 30 days and odd months have 31. This is all for very meta reasons- keeping things simple and familiar to players. This won't be a scifi so much as a very low fantasy setting.

Other than that being very close to Earth's orbit (which I account for other ways), can anyone think of odd implications of that which I may have missed?

More importantly, I have introduced a moon- Triton. About half of Triton's mass was used in the terraformation (needed lots of water and nitrogen e.g.), but the rest of the rocky core is in orbit as a moon. So this remnant masses about 1x10e22 kg, to keep the math simpler. I'd like it's period to be 30.5 days so that lunar months equate very well with calendar months. What would it's orbital parameters be? How much of a tidal effect would this small of a mass have at this distance?

Of note:

Earth's Moon is about 7.342e22 kg.

Assume that Triton's missing mass can be simply added to Venus, plus even more mass from elsewhere, so Venus now masses fractionally more, if that matters- call it 5e24 kg. (It might actually need more water than that, but figuring out that volume and mass is sort of beyond me.)

If I wanted significant tides (other than solar tides of course) and assuming that those parameters didn't produce them, what would the orbit and tides be like if I made it's period 15.25 days so that there are about two lunar months in a calendar month?

Or, if I kept the period 30.5 days with negligible Tritonian tides, what would a world with only solar tides be like? I assume roughly a simple 24-hour cycle, but how much would it "lag"? When would high and low tides generally be?

Or, does anyone have any ideas for a better moon?

Last edited by acrosome; 11-14-2017 at 01:00 PM.
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Old 11-14-2017, 03:08 PM   #2
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Default Re: Implications of a terraformed Venus/Triton

A map for you has been produced here, if you should want it.
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Old 11-14-2017, 03:11 PM   #3
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Default Re: Implications of a terraformed Venus/Triton

Triton contains a lot of nitrogen and water ices, so it would turn into a gigantic comet as a 1/3rd of its mass boils off into space. It would probably last a couple thousand years, but it would rain down ejected chucks of ice and rock every week as it rotated around Venus. Venus possesses around twice the tidal effects of the Earth right now, so it would have twice as high tides with just solar tides.
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Old 11-14-2017, 03:12 PM   #4
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Default Re: Implications of a terraformed Venus/Triton

Quote:
Originally Posted by ericthered View Post
A map for you has been produced here, if you should want it.
I'm aware (I found that site during my research) but I find that map too simplistic. The beginning of my own mapping work is here.

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Originally Posted by AlexanderHowl View Post
Venus possesses around twice the tidal effects of the Earth right now, so it would have twice as high tides with just solar tides.
Not really in my scenario- Venus has been moved out into a near-Earthlike orbit. Review the TL;DR OP, second paragraph.

:)

Last edited by acrosome; 11-14-2017 at 03:32 PM.
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Old 11-14-2017, 03:37 PM   #5
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Default Re: Implications of a terraformed Venus/Triton

That orbit will cause massive instabilities in the orbital mechanics of both planets and, with just a few thousand years, both planets will end up in much different positions, with one likely thrown out and one thrown in. Multiple planets sharing close objects work best in a six-body rosette, where each body occupies the Sun-Objecf L4 of another body and the Sun-Object L5 of yet another body.
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Old 11-14-2017, 03:51 PM   #6
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Default Re: Implications of a terraformed Venus/Triton

The big implication is that you're operating at energy budgets sufficient to actually move planets around (Venus at its current position has a gravitational potential energy of -6e+33J and kinetic energy of 3e+33J. Moving it out to 1 AU will reduce both values by 28%, for a total of about 8e+32J.

This is... several times the gravitational binding energy of Venus, and about a quarter the total annual energy output of the sun. It's enough that almost anything else you might choose to do to the structure of Venus is a rounding error, so you might as well decide what you want it to look like and ignore what it looks like now.
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Old 11-14-2017, 04:53 PM   #7
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Default Re: Implications of a terraformed Venus/Triton

The big problem would be doing it slowly enough so that you do not vaporize Venus. Venus receives around 3.5e17 J every second from the sun, so the energy required to move it is more than 2e15 times as much, the amount received by Venus from the Sun over 60 million Earth years. Even a process with 99% efficiency would have to be done over 600,000 years to avoid the waste heat boiling off Venus (it is much easier, and cheaper, to leave Venus where it is and use its excess atmosphere as reaction mass for increasing its rotation).
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Old 11-14-2017, 05:10 PM   #8
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Default Re: Implications of a terraformed Venus/Triton

OK, first as mentioned above the gravitational interactions between Earth and Venus means that this isn't a stable orbit, especially with the new Venus orbit being so close to Earth's. You are going to get a close flyby of the two within 470 years. At closest approach the force of gravity between the two planets will be greater than the force of gravity between them and the sun, so the orbits will definitely be significantly changed. (If I didn't make any math errors). If you make the period of Venus exactly the same as Earth it will last longer, but eventually perturbations from the other planets will cause the orbit to shift slightly and you will again get a close encounter. For longer term stability, I'd recommend moving Venus away from the Earth--perhaps give it a period of 300 days. It will be warmer, but much more stable.

As far as the tides goes, if I remember correctly the strength of tides is proportional to m/r^3. So since the Triton remnant has about 1/7 of the mass of our moon, it the same distance the tides will be 1/7 as strong. If you move Triton closer so that its period is only 15.25 days, then by Kepler's third law it will be at a distance of 0.62 that of the moon, so the tidal effect will be (again if my math is right) about half of what the Earth-Moon system has.
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Old 11-14-2017, 05:40 PM   #9
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Default Re: Implications of a terraformed Venus/Triton

This is going to sound counter-intuitive to the standard scientific brain power on this forum, but...

Why worry about it?

Start at the end. You have a terraformed Venus laid out the way you envision. It has the remnants of Titan as a moon. Give it a couple more moons for dramatic flavor.

It has the rotation you want, the mass you want, the gravity you want, the weather you want, the seasons you want and the long lost remnants of humanity live there. Just like you want.

How did it come to be? Doesn't matter. It's a low tech fantasy world. Even the brightest scientists are only going to be able to hypothesize or dream of the technology capable of pulling all that off.

What do you want the adventures to focus on? Is scientific accuracy going to play a part in the campaign? What cool things do you WANT to happen on this long lost terraformed Venus? Regular meteor showers? Strange solar storms? Gravity shifts?

I would focus more on what you want and detail that out and not worry so much about the science.

You can also label your setting with a disclaimer... "no scientists were harmed in the making of this setting". :D
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Old 11-15-2017, 06:07 PM   #10
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Default Re: Implications of a terraformed Venus/Triton

Quote:
Originally Posted by AlexanderHowl View Post
That orbit will cause massive instabilities in the orbital mechanics of both planets and... etc etc
Quote:
Originally Posted by a humble lich View Post
OK, first as mentioned above the gravitational interactions between Earth and Venus means that this isn't a stable orbit, especially with the new Venus orbit being so close to Earth's...
Yes, I'm aware. I was going to have Earth in the same orbit on the opposite side of the sun with some sort of surviving active-maintenance mechanism in place. One result being that Jews/Baha'i/Muslims all prayed towards the sun, since that's where the Holy City(ies) are/were, and now sun cults abound. I was actually impressed with my own cleverness, there...

Quote:
Originally Posted by Anthony View Post
...Moving it out to 1 AU will reduce both values by 28%, for a total of about 8e+32J... This is... several times the gravitational binding energy of Venus, and about a quarter the total annual energy output of the sun.
Quote:
Originally Posted by AlexanderHowl View Post
...Venus receives around 3.5e17 J every second from the sun, so the energy required to move it is more than 2e15 times as much, the amount received by Venus from the Sun over 60 million Earth years. Even a process with 99% efficiency would have to be done over 600,000 years to avoid the waste heat boiling off Venus...
THIS, on the other hand, is a problem for me. Hmm. Ok, I'll rethink the setting with Venus kept in it's orbit (or at least very close). I actually liked the idea of a statite soletta in a lot of ways, anyway, though it would also need a surviving active-maintenance system. (I don't like the idea of sunshades a la Ringworld- too obvious.) Though, the statite soletta might make for a decent save-the-world sort of scenario at some point...

So. A 224.7-day year. Hmm.... How ridiculous would the energy budget be to move Venus out just a bit to give it a 240-day year? (That'd be twelve 20-day months, each of two weeks called "tendays." I like neat numbers.)

A significantly massive moon is highly desirable, though. Both for aesthetic meta reasons and for it's stabilizing effect. I'll rethink, again. It seems like there would still be a significant problem with the energy budget to move Titan, though, right?

Quote:
Originally Posted by trechriron View Post
Why worry about it?
Because I do. Just accept that as a given, please, because it ain't going to change. :)

Besides, oddly enough when you stick to the science sometimes it gives you interesting inspirations.

For instance, Venusian geology is entirely volcanic (scoria, granite, basalts, etc.) yet my world is going to have a sort of limestone filling some of the basins that I need to fill on the maps. How? Well, it turns out that one scheme to fix Venus's atmosphere (other than using it as reaction mass) involves precipitating the carbon in the form of metal carbonates- largely, calcium carbonate. There will also be a lot of potassium and magnesium carbonate deposits in deserts.

Also, it turns out that Venusians rocks have deposits of elemental aluminum chondrules! (Often alloyed with titanium, magnesium, and other metals, granted.) So, there will be aluminum (aka "white metal"), and I have had to figure out how that fits into the setting. One place it fits is in making highly corrosion-resistant aluminum bronzes to trade with aquatic peoples. Etc.

Last edited by acrosome; 11-15-2017 at 06:50 PM.
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