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Originally Posted by whswhs
Do you mean five times the diameter or five times the mass? Is it a large terrestrial that's retained helium but not hydrogen, or a small jovian that has a lot of methane, ammonia, water, and so on in proportion to its hydrogen content?
I think the satellite would need to have a really high density to be habitable and earthlike at that size. You can probably tweak the blackbody temperature and density and see what's the smallest planet you can get that comes out as an ocean world.
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I was thinking more in terms of size (diameter) than mass. Visually, what I imagined was a large obvious object, visible in the sky of the game-world (habitable moon).
With the little bit of Google-based knowledge I'm picking up, it seems that a large and solid rocky planet might be too much mass and might risk crushing (or adversely impacting in some other way) the habitable moon. Though, I suppose that could be solved by having the moon further away from the planet.
I like the idea of a mostly liquid planet, but most of the reading I've done indicates that tends to be quite rare, and it's debatable whether or not such a thing is actually possible at the size of something like Saturn.
In the end, the planet itself doesn't particularly matter. For the sake of the game, it's mostly just a visual effect. However, knowing what the visual effects are and how to explain them to my players is something which I feel adds to the game.
For the sake of making the conversation a little easier, I'll name the planet "Primus." The habitable moon which is the game world will be "Unshier."
Quote:
Originally Posted by dcarson
Planets can get in a resonance with what they are orbiting. Mercury is a 3:2 resonance so it rotates 3 times for every 2 orbits.
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That sounds similar to what I had in mind.
As I consider the idea more, I like the concept of Unshier's (the habitable moon) position and visual effects on Primus (the primary planet) being used in a manner similar to how various mythologies use moon phases and other astrological events to explain things here on Earth.
I started to consider that idea after thinking upon the red spot of Jupiter. Depending upon how close Unshier is to Primus, large planetary events could be visible. Magical traditions or rituals might attribute characteristics to the different faces of Primus and patterns on the surface of the planet.
My original question about whether or not navigation would be more difficult appears to have an answer of "no." ...and it may actually be a little easier to navigate using the large object in the sky.