Somes J wrote:I think the simplified rule of thumb is you can have stable orbits up to 1/5 the distance between the companion stars at closest approach. So if the closest approach was 30 AU you could get stable orbits up to 6 AU; big enough to contain Jupiter and everything inside its orbit. I imagine beyond this you'd probably have a large cleared zone, and then maybe a distant cometary halo that orbits both stars. That might be for equal mass stars though, in which case the planet-forming zone would presumably be bigger for the Amillian sun and smaller for the red dwarf.
Indeed. Something else here is the outer star clears things out - but would it have affected planetary formation? I'm hoping yes - it might prevent asteroids from coalescing into planets, thus leaving multiple asteroid belts to mine!
A downside to that would be asteroid bombardment of the planet, but if we're going with terraforming and colonization, that's not a big deal anyway; life needn't survive long there naturally. A million years between asteroid impacts is enough time to get a colony going. (And hopefully, get it cool enough naturally so the terraformers don't have to deal with that. Should be fine anyway.)
Asteroid impacts don't scare the colonists much, due to the timeframes involved, and the confidence that they can handle it. This might be part of a reason why some people stayed in space: those guys would not only be immune to asteroid impacts (habitats can just move out of the way), but they could also protect the planet from them with relative ease.
This works out nicely, as you still have room for the gas giant you wanted.
I'm liking this star system...
Incidentally, binary stars tend to have pretty eccentric orbits so if the closest approach is 30 AU the companion star will probably be quite a bit farther away for most of system's revolution. You probably can't make the closest approach much closer than 25 AU and still have room for the gas giant, unless you make the Amillian sun significantly dimmer than Sol (moving the snow and tar lines inward).
I'm thinking I'll keep the sun very similar to sol itself (this is one reason why the conservative 'luddites' find it attractive - it is very similar to home sweet home).
Eccentricity is ok, maybe put it on an orbit similar to Pluto - 30 AU on its near approach, and 50 AU on the far. Pluto has an orbital period of ~250 years, meaning it's distance would pulsate just about with the century. (Remember how Pluto used to be the eighth planet?! Good times, good times.)
It'd be quite dim when on the far part of its orbit, giving amateur astronomers something to chew on in the olden days, and providing a bit of uniqueness to the environment. I like it.
This also goes back to the asteroid and comet thing. On the aphelion, it might yank fun in from the Oort cloud or Kuiper belt. Space colonists would like this because it shoots in a nice stream of water to the inner system for them, without having to burn out there themselves.
As an aside, it seems to be to be a good idea to use your kinetic energy before you slow down, when entering the system, to knock some of those outer system objects in toward where you intend to be. I'm not exactly sure how to do this - maybe launching missiles? That seems like it would shatter the object instead of changing its orbit, but whatever, any way it is done, it just seems like a waste to decelerate and lose all that energy when you can do so much with it.
Maybe decelerating your ship could accelerate little sailbots into a retrograde orbit in the outer system... hmm... then those sailbots could collide with objects on demand and send them in toward your colony. I wonder if it'd be worth the cost. It sounds cool to me.
Come to think of it, this isn't an original idea. Isaac Kuo on the sfconsim-l yahoo group proposed something similar a few months ago; in fact, I think I'm outright ripping him off here, but not quite sure (I read quite a few ideas over time and they blend with my own forming a synthesis blob in my brain. I then forget all the sources over time, and sometimes forget the underlying assumptions, leading to me sometimes being pigheadedly wrong). But I'll have to look up his emails later and see just what he had in mind.
Incidentally, here's a little issue to consider: does Amillia have a stabilizing satellite?
Yes, it is remarkably similar to our own moon, and has a long history of out of universe things.
In the earliest revisions, when the setting was outright fantasy (not even soft sci fi yet!), their star system was just our's, but in a kind of magical mirror universe. Once you cross through, you start living under the new rules of life, but the setting is otherwise the same. So same Earth, same moon, but the universe had all kinds of magic changing the development of civilization. One of them was a magical teleportation gate up to the moon! (I'm tempted to revive the fantasy iteration here. I had some cool stuff stuck in there, and I really liked the magic system.)
The next iteration was closer to what it had recently. I integrated the universes and shuffled around some of the other planets in the system, but I kept the planet mostly the same. Virtually identical to Earth, still has the moon. Difference here is the moon was no longer populated, but still physically the same. There was no explanation for this; God did it, accept it and move on.
The final iteration included changing the world map around and condensing the amillian civilization geographically in the world, leaving most of it unexplored; the surface changed a lot, but the same physical makeup was still the same as the oldest times: just like Earth and our moon.
I'm still running with that final iteration, but now have a more satisfying explanation than "god did it", in two parts: a) The system is a lot like home, so it is attractive to the conservative folks in the story. Out of the thousands of stars they surveyed, they picked the one that was closest to home. So a sun like star, an earth like planet, and a familiar moon around it. Then b) the terraformers did the rest of the intelligent design / natural evolution (importing Earth life). They nudged what they had the rest of the way to being like home.
Would this make it a popular destination? Well, sort of - two independent expeditions picked it. But more than that? Oh, I doubt it. An advanced civilization wouldn't have a need for a system that looks like the cradle. A closer star is easier to get to, and other star classes may have big advantages for a pure space civilization; hot Jupiters around bigger stars in particular look very cool to high tech space civs, with easy solar power and metals all in space, and lots of gravity assist potential. The hot jupiter here might be somewhat attractive, but not as much as a closer, bigger one.
This system is only uniquely attractive to a very, very small minority of people in the far future of Earth. Enough to have some fun with it, but not so much as to make it hotly contested
But yeah, short answer is it does have a large, stabilizing moon. The other star knocking a dwarf planet in and it being captured might be how it got there - this would be revealed in geology surveys; maybe their lunar soil is quite different than our own moon. But however it got there, it was already close to home when the people decided to go there.
One of the long-term issues with terraforming is a large satellite to keep the axis from wobbling and keep the climate stable - most planets you'd be working with probably won't have a moon like Earth, and it seems to be one of the crucial factors in making a planet friendly to complex life (imagine if the planet flopped on its side like Uranus every few tens of millions of years - that'll really mess up your carefully crafted garden world!).
I haven't really researched this, but would that really be a dealbreaker? It'd have some climate changes, as the poles are now getting direct sunlight, but middle latitudes - like where Europe is - might just work out without catastrophic changes. Life can survive there and expand back to fill in the voided areas.
Or, since it is probably a pretty gradual change anyway, life could always adapt / migrate without having outright extinction events in those areas. (Technological civilizations could handle it even more easily, through migration or staying indoors.)
But like I said, I haven't researched it, this is just a gut feeling.
If you want long term stability you want to move a suitable body into orbit of your planet. I think it can be done - if you have Von Neumanns to cover half of a suitable jovian sattelite with rockets and strip its ice layers for reaction mass! But for a group with more modest tech, well, it'd be ... interesting.
If you have the time to spend on it, a mass driver could do the job... if you have a loooong time to spend.
A problem with a mass driver would be gravitational drag would really hurt the exhaust velocity. As long as the mass is accelerated up to escape velocity, it will accelerate the body, but only by how much it
exceeds escape velocity. Anything under that would be lost as gravity's constant tug reclaims the speed. Man, a big move would have to blow off a huge mass of the body, since this means poor specific impulse... not really attractive there either, but it could be done in theory.
Hey, speaking of gravity tugs, that's another method that might work, avoiding the loss under escape velocity too. Again though, it'd burn through a lot of reaction mass (big asteroid... hey, how would you get a big enough gravity tug in position in the first place? Gah, this might be a chicken/egg situation). And, even if it does work, it'd take a looooooooooong fucking time to do the job.
Attaching millions of magical fusion torches would be a much nicer alternative.
The pole swings take many thousands of years, so in the short term it probably wouldn't be a serious issue. It might also be easier to set up some sort of mirror and sunshade system to control the climate over the long term than to bring in a moon - I didn't use that because I wanted a system that could last into geologic time without maintenance, so humans could find lots of long-abandoned terraformed worlds with ecologies that had been evolving divergently for hundreds of millions of years.
Yea, you can always handwave exactly how they did it. Maybe throw a bone to the reaction mass thing by saying "hey wasn't there a Mars here at some point?"
(alternatively, "man this moon is strangely like the naked core of a planet...")
Might be an interesting issue to touch on for the future - the Amillians might have some sort of long-term plan to move a moon into orbit of their world to stabilize the terraforming, or set up some sort of massive mirror and sunshade system. Or move everyone into habitats.
Coincidentally, they do set up some small mirrors, and most everyones indeed move into habitats near the end. But not for physical reasons. The little mirrors are to improve the efficiency of agriculture on the ground, letting farms in the north grow stuff from the equator and get bigger yields*, and they end up going to habs after a biological weapon slashes the population way way down**.
* I'm not sure if I'll keep the superfarms around. They are a cool application of space tech to the ground, but it isn't really necessary for them. There's plenty of usable farmland around anyway, and shipping stuff in is no big deal. But it is cool anyway!
** The "A'millian holocaust" I'm mentioned a few times scattered around. It cuts their population down to ~15,000. They manage to stabilize the situation, but realize that it can't work long term. They'd be very dependent on the human space colonies to maintain their status, who are willing to help, but figure they might as well just go up there and integrate completely.
The last scene to this part of the saga is mr and mrs author insert, the only two to stay behind at their old home, hitting the launch button for the last group of people to go into space, which includes their grand daughter. They they walk off alone to the empty world.
Anyway, mirrors and shades were used in the old iteration on Earth too - they were used to stabilize the climate while global warming greenhouse gas problems were fixed up. (I'm going to miss that whole section, now that Earth is out. There were lots of cool tech fixes I worked in there to fix up the peak oil and global warming stuff, and some heartwarming moments of cooperation... and of course, some tough love at times. Yay orbital bombardment!)
Just another reason habitats make more sense than terraforming.
Aye.