Is this stretching the bounds of realism too far?

Reservoir Angel · Sep 24, 2011

For clarity sake, the novel I'm writing this question in reference to also features steam punk technology, a world healing itself from near death because of destructive magic, and people who can magically turn into wolves. Just so you know what kind of world I'm working with here.

So now I ask this question: is it in any way feasible to have two small-ish planets sharing an orbit and an atmosphere without, you know, ripping themselves apart?

See I had the theory that these two planets are in balance with one another. So instead of one orbiting around the other, like our Earth and moon set-up, they stay exactly opposite one another, both orbiting around some kind of gravitational anomaly directly in between them.

It sounds like the crazy kind of soft science nonsense that one could get away with, but I have reservations about running with it.

To clarify, this isn't about if it's possible since the magically injured planet and enchantment-based werewolf people render realism totally abstract in this situation, I just want opinions on if it makes any real sense.

Filigree · Sep 24, 2011

If you just look at it from the science angle, then probably not feasible. They'd have to be far enough apart that they wouldn't crash into each other, which means stretching the atmosphere over millions of miles.

But if it's fantasy, go for it. Find an internal logic, and the science geeks will be swept alone with the story.

leahzero · Sep 24, 2011

Orbit yes, atmosphere no...probably.

An atmosphere is held in place by gravity. If the central mass is a gas giant and the two planets were small moon-like satellites, it could theoretically* enshroud them. But it's unlikely the atmosphere would be humanly breathable, and the gas giant probably won't be habitable.

The question is, why do you need the two planets to share an atmosphere? If you take this criterion out, it makes things a lot simpler. Just have them orbiting some central mass.

* But being close enough to be inside the atmosphere will likely result in the satellite also being close enough to be drawn in by the gas giant's gravitational pull, causing it to crash into the body it's orbiting.

Allen R. Brady · Sep 24, 2011

If they do have to share an atmosphere for plot purposes (say to allow a plague to spread between the two), then that gravitational anomaly has to be what accounts for it. The whole system wouldn't be contained within a single atmosphere, but perhaps the anomaly establishes some kind of vortex between the two worlds.

TheRob1 · Sep 24, 2011

from a scientific standpoint I don't think it's possible, however, for a fantasy story I could see it working.

You might want to consider a short myth for why it is the way it is, but when it comes to fantasy you can simply say: that's the way it is.

Reservoir Angel · Sep 24, 2011

Allen R. Brady said:
If they do have to share an atmosphere for plot purposes (say to allow a plague to spread between the two), then that gravitational anomaly has to be what accounts for it. The whole system wouldn't be contained within a single atmosphere, but perhaps the anomaly establishes some kind of vortex between the two worlds.

It's not a reason like that, it's mostly because I can foresee it being incredibly difficult to explain how steampunk technology is able to make inter-planetary starships.

Snick · Sep 24, 2011

If the twp planets orbitted around their common center of gravity and were the size of Mars or smaller, then it might be possible for their atmospheres to meet. Their mutual orbit would have to be as small as possible.

Anne Lyle · Sep 24, 2011

Go for it. The anime series Vision of Escaflowne has an invisible planet called Gaia orbiting close to the Earth, but there's enough magic in the story that the viewer happily suspends disbelief.

Psychomacologist · Sep 24, 2011

Could you just have some sort of magical, interplanetary wormhole-ish "bridge" between the two planets? Then the steampunk ships could sail down the bridge without needing the planets to share an atmosphere.

Anne Lyle · Sep 24, 2011

I don't see the problem in having interplanetary steampunk ships, myself. H G Wells sent men to the moon in what was effectively a modified bathysphere.

Reservoir Angel · Sep 24, 2011

Anne Lyle said:
I don't see the problem in having interplanetary steampunk ships, myself. H G Wells sent men to the moon in what was effectively a modified bathysphere.

I agree steampunk ships aren't the problem. The problem is justifying how such ships exist when the rest of the society are still primarily using swords and handheld weapons in combat, with firearms being a growing but still somewhat unused innovation.

Anne Lyle · Sep 24, 2011

Maybe there's a steampunk-science reason why gunpowder is hard/expensive/dangerous to make? Hence other technologies have moved on, but not fire-arms.

OTOH you could have awesome repeating steampunk crossbows without gunpowder. Though they wouldn't be very portable, so there would still be a need for handheld weapons.

Dave Hardy · Sep 24, 2011

There's a Michael Moorcock novel, Phoenix in Obsidian iirc, where the protagonist comes across the Moon stuck in the side of the Earth like a tennis ball embedded in a big ol' melon. It was completely unrealistic & a wildly vivid image that sticks in my head.

Personally, as a reader I'm more interested in the vivid image than making the author show their math & prove they got it "right." I kind of like the bathysphere idea Anne mentioned. There's a certain "Sword & Planet" vibe to the scenario you describe. ERB's heroes had access to guns but preferred swords, partly because the decaying technology of Barsoom made guns difficult to manufacture, but mostly 'cuz swords are cool.

MJNL · Sep 24, 2011

If it's fantasy, you've got more leeway than sci-fi. Realism only goes so far, and as long as things are internally consistent, you'll probably be ok.

And just a note: gravity does play a huge part in retaining atmosphere, but a planet's magnetic field is actually more important when it comes to a thick one. It keeps the solar winds from ripping it away. So, if they shared a unique magnetic field you could have them sharing air and utilize the unique magnetism for some interesting tech.

Of course, I'm not sure how characters would know all these "scientific" details with the level of tech you've described, but I'm sure it can be worked out.

Sounds fun.

C. G. Hagy · Sep 24, 2011

There was the old Spelljammer setting for D&D, where the whole point was taking fantasy-styled medeival type ships into space and having crazy space pirate battles and such. Basically each ship was fitted with a magical device that created a tiny "atmosphere" of breathable air, heat, and gravity around the ship. You might be able to come up with a similar reasoning.

kiplet · Sep 24, 2011

Robert L. Forward did the math for you.

Mental Traveler · Sep 24, 2011

You could say a bunch of magic user united their will in the past and magically tied the plants together or something.

RichardFlea · Sep 24, 2011

Larry Niven's 'Ring world' has a planet that is a ring orbiting a sun. Why not have a big donut shaped planet (with the sun in the middle) that has some big chasms in it that can only be crossed by airship. Alternatively, one of the first spaceship to the moon was a train fired from a cannon with a pointy nose (which movie was that in???). Why not travel that way, like a submarine in space.

Or, you could have your planets on opposite sides of the same sun in the same orbit (also already done, but I cannot remember where..? Some science fiction movie... any help guys...) Then the 'space submarine' just has to pop up and wait 180 odd days for the second planet to come round, then land. That sounds logical.

Alternatively, just have the one planet and some big obstalce that can only be crossed by airship (chasm, mountain, vortex, krakken infested water...)

RichardFlea · Sep 24, 2011

Another idea, have two planets in opposite sides of the sun (as mentioned before) and a ring of atmosphere, like saturns rings, that is held in place by some freak magnetic ring around the sun?

After all, you can create worlds and conquer armies!

Dreambrewer · Sep 24, 2011

As kiplet pointed out, it's called a Rocheworld, and I too have such a system as the central of my longest writing project. It is quite interesting in my opinion, because it affords the chance to make completely unique cultures and landscapes have a first contact in a pre-space era, among other things. Especially if they've had radio-contact before really seeing each other, except for lights on the other planet in the night sky.

As for the preferance for melee weapons, you can easily sidestep it by making the power-source/reason for flying of the ship be non-technological. Perhaps it is some rare mineral that can be mined, but is in low quantities, or the hearts of dragons or such. That way the level of technology(or magic) does not matter, because the reason why the ships fly is not connected to it. You can use the same reason really for gunpowder and firearms. Perhaps the technique to create gunpowder was perfected just a while ago, it isn't linked to steam-technologies in any way as such, or it requires a special thing that can only be found in larger quantities now(fell from the sky 10 years ago or such).

For more in detail physics stuff about it see here:
http://everything2.com/title/Roche+World

jjdebenedictis · Sep 24, 2011

If I'm not mistaken, The Integral Trees by Larry Niven featured a single world orbiting its sun with a "trail" of atmosphere that ringed the star. I recall it was based on a moon orbiting one of our solar system's gas giants that similarly has left a ring of its atmosphere hooped around the gas giant.

So it might be plausible to have two planets with a ring of atmosphere that connects them. Try reading Niven's book (even just the Wikipedia entry is pretty enlightening) and see how he explained the science.

Invincibility · Sep 24, 2011

Maybe breathing in space is just possible in this universe. If it's fantasy/steampunk, I think that's the sort of thing that could just be handwaved (maybe with a bit of light lampshading).

Reziac · Sep 24, 2011

What if the atmosphere was also orbiting, somewhat like one of Saturn's rings, and the two planets move within this band of atmosphere? That doesn't even require much handwaving. Someone with better Physics-Fu can probably explain why it would/n't work.

frimble3 · Sep 24, 2011

Reservoir Angel said:
I agree steampunk ships aren't the problem. The problem is justifying how such ships exist when the rest of the society are still primarily using swords and handheld weapons in combat, with firearms being a growing but still somewhat unused innovation.

Abandon the firearms, explosives were never developed (something missing in the necessary materials). This frees up time and engineers for the precision work needed for fancy steampunk stuff. The lift for the ships is provided by something else - some kind or rare element, or such.
Either hand-wave the breathable air between the planets, or, aerial submarines.

richcapo · Sep 25, 2011

I love out-there, whacky stuff -- just write the characters well, have internal logic to the magic, provide compelling plots, et cetera, and whatever crazy stuff you're drumming up should work. Don't sweat that "hard/soft" stuff, I say. Just write a great story.

_Richard

Is this stretching the bounds of realism too far?

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