Torn and Its Two Moons

[Ashenvale]

Here's an early concept illustration I've been working on for The World of Torn, an awesome Pathfinder campaign setting that you can check out (and should!) here: The Torn World Forums - The Main Gate

This draft diagram will accompany a dozen-page written document, also still in draft form, covering possible configurations for the two-moon system, including everything from basic orbital and tidal science to the effects of one prograde and one retrograde moon on tides and culture, how two moons affect perigean spring and neap ocean tides, albedo consequences for night-time illumination, and numerous other topics.

[Ashenvale]

For the curious, The World of Torn incorporates several of our world's ancient pantheons, including many of the Old Norse deities. In Old Norse mythology, Sköll (meaning "Treachery") is a wolf that chases the horses that drag the chariot which contains the sun through the sky every day, trying to eat her. Sköll has a brother, Hati, who chases Máni, the moon. At Ragnarök, both Sköll and Hati will succeed in their quests.

Alyssa Faden, the creator of Torn World, named her two moons Hodr and Mani. I am proposing placing two small satellites, spinning around each other as they orbit Mani's L5 Lagrange point, and naming them Sköll and Hati. They will appear to be chasing Mani in its orbit around Torn.

We'll see what Alyssa thinks!

[damonjynx]

Hi Ashenvale,

Nice map.

A couple of inconsistencies in the text though. Legrange is spelled (spelt?) differently in the bottom text box compared to those on the map itself. Mani and Hodr are interchanged in the bottom text box.

[Ashenvale]

Hi Ashenvale,

Nice map.

A couple of inconsistencies in the text though. Legrange is spelled (spelt?) differently in the bottom text box compared to those on the map itself. Mani and Hodr are interchanged in the bottom text box.

Yep. Good catches! It's a draft. Lots more changes coming before tight analysis.

[amberroberts09]

Yep. Good catches! It's a draft. Lots more changes coming before tight analysis.

Yes you are right...

[Ashenvale]

Here's and updated version.

For a variety of reasons, I'm considering changing the angle of Mani's orbit, increasing its present 5-degree angle from Torn's Ecliptic Plane (around its closer sun, Odur) to a 15-degree angle. This would make Mani's path across the sky swing, over the course of a sidereal month, both 15 degrees north and 15 south of the path that the sun Odur follows across the sky. This is visually more interesting but makes tidal calculations, which are already complicated, even more so.

For purposes of this diagram, the alteration presents a challenge. Lowering the green line of Mani's Orbital Plane 10 degrees pushes the image of the moon itself down far enough to squish it against the box containing the images and text for The Wolves. I'd have to move The Wolves' box over to the lower right corner and put my signature in the lower left. Moving the orbit would also make the angles of the two main moons' orbits far more similar, closer to equally balanced off of Torn's Ecliptic Plaine. This seems likely give the entire image too much visual symmetry for my tastes.

While I know I cannot let map design govern planetary system development, it always hurts to diminish an image's visual effect!

[damonjynx]

It's fantasy right? My maxim in my games is, "Never let the rules get in the way of a good story". Real world considerations should be secondary to 'design' & 'story' elements IMO. Go with what looks good and is reasonable. All the rest can be put down to anomalies within that star system - i.e. orbiting moons and so on that don't follow the same 'rules' as our solar system...you get what I mean.

[Ashenvale]

It's fantasy right? My maxim in my games is, "Never let the rules get in the way of a good story". Real world considerations should be secondary to 'design' & 'story' elements IMO. Go with what looks good and is reasonable. All the rest can be put down to anomalies within that star system - i.e. orbiting moons and so on that don't follow the same 'rules' as our solar system...you get what I mean.

I couldn't agree more, damonjynx!

My only point is that the desire to make the most visually appealing map should not overrule decisions about how best to construct a world, or a planetary system, for game-play. Like any illustrator, the commissioned RPG cartographer's job, as I see it, is to make clear, understandable, and attractive the physical design of a place (or solar system) created by the publisher or game designers.

Beyond this map, I'm involved in helping to craft this planetary system for The Torn World. This is the hortatory language at the beginning of my lunar-structure proposal to the publisher:

There are three principal objectives when designing a two-moon planetary system for a PFRPG campaign setting. First, the system has to be flexible enough to allow a GM to do with it what she wants. If the GM needs a solar eclipse (or two at once), she should be able to produce one without “breaking” the players’ understanding of how and when things occur. If she needs an exceptional high tide, or a moment when the tides stop utterly, the system should make that available to her.

Second, the system should be reasonably founded in science. The goal is not to survive intense scrutiny from that anally retentive Ph.D. physicist player whose main joy in gaming is highlighting with outrage minute errors. This is Pathfinder, not GURPs Space. Rather, the objective is to ensure that the system passes basic scientific muster so that players with a fundamental understanding of astronomy don’t find themselves jerked out of game immersion by a clearly absurd occurrence. Let physics do the bulk of the heavy lifting and reserve magic for occasions when an adventure’s narrative or the setting’s inherently magical characteristics makes altering physics both justifiable and necessary.

Finally, and most importantly by far, the world the planetary system creates has to be thrilling. Readers should want to play there. Players should want to go there. And stay there. This means the world should be visually stunning. The dual moons’ effects on everything from illumination to tides should create a sense of wonder and surprise. The dual moons should alter culture, religion, and day-to-day life in obvious ways but also in subtle ways that take innumerable gaming sessions of play to discover. The system should be another world, a more exciting world than ours, full of more brilliant light, deeper darkness, and endless wonder.

[DrunkenEwok]

Call me the anal retentive PhD physics player - but this system does tend to strain credulity, and I'm not even that good at planetary physics (so take everything I say with a healthy grain of salt). You're more than welcome to just handwave the physics or call it magic - but the synthesis of the two (physics and magic) makes suspending disbelief a little harder (at least for me). I'm a huge fan of more complex planetary systems for interesting fantasy worlds - but I must say I've never incorporated quite so many different elements into a single world.

My chief concern isn't that you have two moons, or two exceptionally large moons, or a moon with rings, or a moon orbiting one of those moons, or that neither of the moons has approached tidal locking, but the addition of not one but two separate L5 systems are pretty unusual in a system this complex. L5 (and L4) are incredibly stable orbit points - but only for a two-body system. Once you add another body of any non-trivial size in close proximity, that body tends to destabilize the Lagrangians of the two-body system. You can feasibly have Hodr and Mani - but unless one of them is really small or really distant, I wouldn't also include the Wolves and the Tears.

Let's say, for the sake of the story, you want to keep all of the major elements currently in play, but you want to keep some semblance of real-world physics to explain it:

• Unless the world is really "new" (and thus probably long-term unstable) I would tweak Mani to be tidally locked with no angle from it's plane of revolution - as the closer moon, it's the most affected by Torn's gravity and likely to get captured over the geologic timescales necessary for life
• Keep Mani's rings - but make them pretty close in, and relatively dim - like nearly invisible except when Mani is in the new moon phase
• Increase Hodr's axis of revolution by 10-20% - putting it further out decreases the likelihood of tidal locking and interference with Mani's Lagrangians.
• Hodr's moon - which I assume is on the scale of a small asteroid (ala Phobos/Deimos) (and does it have a name?) - needs to be pretty close to avoid perturbation by the rest of the system
• To dramatically decrease the Lagrangian instability, you could put Hodr and Mani in opposition - i.e. they'd have the same orbital period and always be on opposite sides of the planet - obviously this makes having both moons in the sky simultaneously impossible, which is less story fun. As a compromise - you could try some level of orbital resonance - maybe a 2:1 or 3:1 resonance would lend some stability to both systems - but I can't say for certain without doing the math - and I'm not even sure I could with a system this complex (plus it's been 10+ years since I've tried at all)
• Skoll and Hati - I'd probably reduce to just one Wolf given the system instability, but if you're keeping both, make them very small and tightly bound to each other (otherwise one or both will wander out of the Lagrangian region and get spun out of the system) - they'd almost have to be very small, looking more like a pair of stars chasing Mani rather than moons themselves.
• As for the Tears - my instinct is that from the planet, given the size/distance of the particles, I'd imagine it'll look more like a fuzzy cloud (similar to the Milky Way) that twinkles occasionally - if you want them to look more like a herd of stars, they'll need to be reasonably sized, which dramatically increases the likelihood that they'll coalesce into a single body. You could also assume that the instability of the L5 point (due to Mani's influence) is what keeps the Tears broken up.
• Another possible addition - if the system managed to recently collect a large amount of high-albedo particles, that could help explain both Mani's rings and the Tears - my best idea would be a major comet impact with Mani, which would fill the entire system with debris, causing some spectacular meteor-shower effects on Torn itself for a few months/years (campaign background?), Mani reclaims a fair portion, but some falls into a ring pattern - meanwhile most of the rest gets cleared out, until only the Tears (and maybe a companion set at Hodr's L4?) remain

The easier answer is to say screw the laws physics, and just use them when you feel like it.