[Space] Terraformed Venus as a setting

[acrosome]

Originally Posted by Proteus

In fact, I think Venus' solar tides ought to be about three times the size of Earth's

How interesting... How would that work? High tide at noon and midnight? (That would make book-keeping much easier, if nothing else.)

How could I verify that the Cytherean solar tide would be that large? If so, I guess I don't need a moon, unless the L3 "counter-Earth" thing is doable.

[David Johnston2]

Originally Posted by acrosome

How far out could I move it without adversely impacting Earth's orbit, and how long would the year be? Could I move it into Earth's L4 or L5?
I found a lot of stuff online about Lagrangian planets but everything seems to assume that one is much larger than the other, which would not be the case here, so I have no idea what the repercussions would be.

Without a great size disparity no lagrange point is at all stable.

A world without a moon would actually make for a pretty interesting setting, but it has problems- no tides,

No lunar tides. The solar tide still exists and would be a bit stronger. Tides on Earth were actually a bit of a challenge to work out because there were two different tidal forces and you had to account for both. But Venus still has a tide.

Venus's current solar day is 116.75 [24-hour Earth] days long. Unworkable. I found various terraformation schemes online that could explain spinning it up as fast as a 14-day solar day.

In order to cool Venus down you need to have sun shades in orbit. The sun shades would break up the "day" into shorter day/night periods.

That actually intrigued me- having the "fortnight" as the basic timekeeping unit- but I've decided that it probably causes a lot of problems, and would likely raise the suspicions of scifi-fanboy players. Having the sun rise in the West is odd enough to keep things interesting for my purposes.

And...how would they know that the sun is rising in the west?

[johndallman]

Originally Posted by PTTG

If you want to show just how powerful these people were, go ahead and put it in a mutual orbit with earth.

That needs on-going maintenance. And PCs have a tendency to get into the machinery and, well, be PCs at it.

I have played a fantasy campaign that was about getting the machinery in a much wackier setup sorted out after the Lords of Chaos had got at it, but fortunately, they never do anything properly.

[acrosome]

Originally Posted by David Johnston2

And...how would they know that the sun is rising in the west?

Good point- I could just rotate my map 180 degrees. (Which as a bonus might further obscure things for the scifi fanboys.) I think that the names of the cardinal directions might survive, but I can work around that. Say… when the new magnetosphere worked itself out north was south and south was north, then they just designed east as "where the sun comes up." Great idea. It also plays to some of my other goals regarding which civilizations are on which continents.

Originally Posted by David Johnston2

In order to cool Venus down you need to have sun shades in orbit. The sun shades would break up the "day" into shorter day/night periods.

Yes, such solutions are a common trope, but I'd rather not give the game away quite that blatantly.

[Diomedes]

Originally Posted by acrosome

Yes, such solutions are a common trope, but I'd rather not give the game away quite that blatantly.

There's also the problem that just putting sunshades in orbit to break up the day won't do anything to break up the night.

[Agemegos]

Originally Posted by acrosome

First, Venus's year is 224.7 [24-hour] days. That's workable, but if I wanted to is there a larger orbit to which I could move Venus safely- i.e. without doing horrible things to the Earth? How far out could I move it without adversely impacting Earth's orbit, and how long would the year be? Could I move it into Earth's L4 or L5?

You couldn't move it very far without introducing potentially-dangerous orbital perturbations with Earth. Out to about 0.75 AU, maybe. The planets are pretty tightly packed, and Earth-Venus is the smallest proportionate gap. Venus is ten times too massive to be in a stable L4 or L5. Without active station-keeping you'll get another giant impact like that which is supposed to have formed the Moon.

But if you have the power to move planet's orbits you might not care. You could use the same technology for active station-keeping. And if there were a breakdown you would have decades to mend it before everyone of both planets was killed.

I found a lot of stuff online about Lagrangian planets but everything seems to assume that one is much larger than the other, which would not be the case here, so I have no idea what the repercussions would be.

The minimum mass ratio for objects to be stable in a Lagrange-point configuration is about ten, I think. Repercussions would look like the formation of the Moon under the Giant Impact Hypothesis.

Would both planets orbit their respective Lagrange points, like Trojan asteroids?

Yes. In unstable Lissajous orbits until they collide, one hits the Sun, or one gets ejected on an escape orbit.

None of the other Langrangian points work- L3 was very tempting, but it is unstable on the order of 150 years.

If you can move Venus, you can fix whatever it might do to the Earth. You could even move it into one of Earth's Trojan points: it's too massive to be in a stable orbit there but you don't care. If you can move planets you can employ active station-keeping for them. But wow! You can move planets. Colourful but obscene Australian colloquial expression of astonishment!

A world without a moon would actually make for a pretty interesting setting, but it has problems- no tides, impact upon some forms of wildlife, etc. Plus, everyone likes moons and adding a moon to Venus would, again, help disguise the planet's identity from the scifi fanboys. So I'm thinking about finding an appropriately-sized body (or two) in the solar system and moving it to be Venus's new moon. Anyone have good ideas for candidates?

Mercury. Ceres.

Input?

Smack Mercury into Venus to simultaneously spin it up, alter its orbit, make it a moon, Boil off excess volatiles, and melt its mantle to give it plate tectonics.

Originally Posted by Proteus

You don't need a moon to have tides; Earth has both lunar and solar tides.

In fact, I think Venus' solar tides ought to be about three times the size of Earth's (1.0 AU / 0.7 AU cubed) — and, since Earth's solar tidal force is 46% as large as the lunar (see http://en.wikipedia.org/wiki/Tide#Forces ), that means you'd actually have tides roughly equivalent to Earth's even without a moon.

It's because of these large tides that its rotation is so slowed. They might also be the reason it has no moon.

Originally Posted by tbrock1031

For the Lagrange points, the L4 and L5 points are 30 degrees

60 degrees.

Originally Posted by acrosome

How interesting... How would that work? High tide at noon and midnight?

That's right for the primary driving tide, but basin resonance effects are going to give each spot a characteristic lag.

Originally Posted by acrosome

Say… when the new magnetosphere worked itself out north was south and south was north, then they just designed east as "where the sun comes up."

East is defined as "the direction where the Sun rises". It was named before the magnetic field was discovered, and the "north" and "south" poles of a bar magnet were named after the directions to your left and right as you face East, not vice versa.

[sir_pudding]

Originally Posted by acrosome

Yes, such solutions are a common trope, but I'd rather not give the game away quite that blatantly.

I find that players almost never catch on to this stuff. Call the sunshades "gods" and have them be worshiped by the local religions complete with elaborate pantheonic soap opera drama and you'll probably get the players taking them at face value.

[David Johnston2]

Originally Posted by Diomedes

There's also the problem that just putting sunshades in orbit to break up the day won't do anything to break up the night.

I wouldn't class that as a problem so much as an interesting exotic feature.

[johndallman]

Originally Posted by Agemegos

Smack Mercury into Venus to simultaneously spin it up, alter its orbit, make it a moon, boil off excess volatiles, and melt its mantle to give it plate tectonics.

It'll take a while to cool off again, but apart from that, what could possibly go wrong?

[David Johnston2]

Note that this defeats the whole idea of using the map of Venus.