[Space] Terraformed Venus as a setting

[Agemegos]

If you give Venus an Earthlike rotation then initially the sea level will be twenty-one kilometres higher at the equator than the poles. The atmosphere will accumulate at the equator too, giving the polar region the atmospheres of mountains at 21,000 metres altitude: 70,000 feet.

The mantle will conform to the geoid over a timescale of a few millenniums. That will open up rifts at the equator totalling 65 kilometres wide, and cause corresponding buckling in the polar regions. Since the mantle is viscoelastic it will approach equilibrium by a negative exponential, i.e. fast at first. The energy released will appear as heat, warming and softening the mantle.

[lwcamp]

Originally Posted by acrosome

Is Mars small enough that this would work? If they are too close in mass a 'planetary rosette' is unstable, right? Or is it just the 3+ rosettes?

Any two-body system has stable orbits. All ideal two-body orbits are stable (real-world complications limit you to orbits outside of the atmosphere/hydrosphere/lithosphere/Roche limit of the companion body). So yes, you could get Mars orbiting Venus, Earth orbiting Venus, a perfect clone of Venus orbiting Venus, and so on (techically, in all these cases the two companions would be orbiting a common barycenter outside of either planet rather than having one planet being orbited by the other, but this is a minor point).

If you want additional moons, you can put them at the Lagrange points of the Venus-Mars systems (after all, Deimos and Phobos need to go somewhere), or they could orbit much closer to either Venus or Mars than the Venus-Mars orbital distance.

Originally Posted by acrosome

It also increases the habitable area of a planet. Do you think that Alaska would be habitable if Earth didn't have a significant tilt?

If you just took our modern planet and just changed the inclination to 0, it is hard to say because of all the knock-on effects. The climate of Alaska depends on so much more than the inclination (for about 10 million years during the Eocene, it had a climate similar to Florida. Since the rest of the world was clearly not uninhabitable at this time we have an example of a season-free planet with arguably more favorable habitibility than Holocene Earth). You really need to take careful consideration of the heat transport, and it probably needs a full climate model simulation to get a good answer. For a game, you could make it swing either way and still be plausible.

Luke

[lwcamp]

Originally Posted by Agemegos

How do you feel about tropical cyclones? There are some passable universities in Queensland.

Sounds delightful. Maybe not the cylcones so much, which could be endured, but the climate and wildlife. Biggest problem is that both sets of my kid's grandparents are here in Washington Stae's Tri-cities, which ends up being sort of a big thing. I wonder if I could convince all of them to move to Queensland?

Luke

[panton41]

You might handwave real science and look at old science fiction for inspiration. At one time it was a popular image to have Venus covered in rain forest and Mars be a habitable desert. You could just ignore real science from about 1962 onward and go with what you want. In that case I'd look to GURPS Tales of the Solar Patrol for inspiration. (For that matter I used to belong to a sci-fi writing club run by the author of that book. He actually goes by Lizard in person.)

[Agemegos]

Originally Posted by lwcamp

Sounds delightful. Maybe not the cylcones so much, which could be endured, but the climate and wildlife. Biggest problem is that both sets of my kid's grandparents are here in Washington Stae's Tri-cities, which ends up being sort of a big thing. I wonder if I could convince all of them to move to Queensland?

It is a popular place to retire to. Like Florida, but with its own Texas. There's no-where like it on Venus.

[acrosome]

Originally Posted by Agemegos

If you give Venus an Earthlike rotation then initially the sea level will be twenty-one kilometres higher at the equator than the poles. The atmosphere will accumulate at the equator too, giving the polar region the atmospheres of mountains at 21,000 metres altitude: 70,000 feet.

Ok, what am I not grasping, here? Since Earth has an "Earthlike rotation", then why doesn't Earth's atmosphere stack at the equator as well? Yet Prince Harry isn't having trouble breathing at the South Pole…

Or are you talking about before Venus deforms into a more oblate spheroid?

[Flyndaran]

Originally Posted by acrosome

Ok, what am I not grasping, here? Since Earth has an "Earthlike rotation", then why doesn't Earth's atmosphere stack at the equator as well? Yet Prince Harry isn't having trouble breathing at the South Pole...

Venus has an incredibly slow retrograde rotation. Spinning that puppy up to earth speeds must have some kind of dynamic effect on an atmosphere. I don't have a clue of what type or severity, but the concept makes sense.

[Fred Brackin]

Originally Posted by acrosome

Ok, what am I not grasping, here? Since Earth has an "Earthlike rotation", then why doesn't Earth's atmosphere stack at the equator as well? Yet Prince Harry isn't having trouble breathing at the South Pole…

On Earth the effect is overcome by temperature related density effects. Cold air is denser and warm air is thinner.

[Agemegos]

Originally Posted by acrosome

Ok, what am I not grasping, here? Since Earth has an "Earthlike rotation", then why doesn't Earth's atmosphere stack at the equator as well?

Because Earth's mantle conformed to the equipotential surface, raising the the ground level at the equator by 21 kilometres. The geoid is approximately an equal-energy surface, so the water and air conform to it.

If Earth were to stop rotating first the air would pile up at the poles, then the water would do so, and gradually the mantle material would follow, displacing the oceans and air back to equatorial regions — but rifting the crust in the polar regions and producing mountain chains across the equator. This is the reverse of that. If you make Venus spin faster its air will accumulate in an equatorial belt; oceans when the terraforming produces them will also accumulate in an equatorial belt; but over a few thousand years the mantle material will also shift to the equator, giving Venus a more oblate shape in equilibrium between its gravity and rotation. That movement will open rift valleys crossing the equator, which will have lots of volcanic activity, and it will raise mountain chains by lateral thrusting in the polar regions. Those will put all your maps out of date.

I expect Prince Harry will no longer be relevant by then.

Originally Posted by acrosome

Or are you talking about before Venus deforms into a more oblate spheroid?

That's right. When it does so conform it won't be a smooth stretching. You will get rifting parallel to the meridians in the equatorial regions, producing rifts valleys and extensive vulcanism. In the polar regions the opposite as the crust bunches up over the subsiding mantle, with thrust orogeny. And this all means big changes to the map.

Originally Posted by Fred Brackin

On Earth the effect is overcome by temperature related density effects. Cold air is denser and warm air is thinner.

No. On Earth the effect produces an equatorial bulge of the planet's surface which in equilibrium countervails the effect because the air, water, and mantle material all conform to levels of the same potential field.

[acrosome]

Originally Posted by Agemegos

Because Earth's mantle conformed to the equipotential surface, raising the the ground level at the equator by 21 kilometres. The geoid is approximately an equal-energy surface, so the water and air conform to it.

So, yes, you're talking about before the planet's surface conforms to its new geoid.

Crap. Why can't this be easy?

Happily, most of the equatorial land surface already has extensive rift systems.