Smaller Planets

[Ed_Laprade]

Gravity is largely a function of mass. So, as a poster above said, make it even more metal rich than earth and it should be believable.

And that's where all the gold, mithral and adamantium comes from!

 

[Ripzerai]

One more thing: distance from the sun... this planet is smaller, so I guess the planet would have to be farther?

I don't see any correlation between planetary mass and distance from the primary. Mercury is smaller than the Earth, yet it's closer to the Sun. Venus is about the same size of the Earth, but it's closer to the Sun, too. Jupiter and Saturn are far more massive than the Earth is, but they're much further away from the Sun.

 

[Nonlethal Force]

One more thing: distance from the sun... this planet is smaller, so I guess the planet would have to be farther? Does that have any effects?

Planet size has little to do with distance to the sun. Mercury is one of the smallest and it is the closest. Pluto (up until about 4 months ago) was also one of the smallest and it is the furthest.

If you are talking about radiant heat, that is a function of distance. Think of a candle flame. The closer you are to it, the warmer it is. There is a certain distance where you can feel little heat from a candle and a certain distance where it is too hot. The sweet spot is where is is warm enough to be comfortable but not warm enough to burn you. So it is with the sun as well.

 

[BRP2]

Oh, no, I don't mean size being caused from distance from the sun lol...

Maybe I'm an idiot, but I was just thinking that, for things to be just like earth, in terms of the equator and polar caps being roughly proportional in size to it, wouldn't the angles have to be just right?

 

[Plane Sailing]

I imagine your horizon would be closer on a small world, and there might be a perceptible curvature of the horizon.

 

[phindar]

I've always worked on the theory that the typical D&D world is much larger than our own, with a much higher gravity, and the mini's we use are actual size.

 

[S'mon]

Because of the way gravity works (proportional to volume, decreases with cube of distance), for a given density, gravity at surface is proportional to diameter of planet. So half the diameter (or circumference) = half the gravity.

 

[jmucchiello]

I failing to see how any of this matters. Say the sky is orange. If you and everyone you ever met were born on a planet with orange sky, you wouldn't care that it is orange. Unless you constantly beat your players over the head that they sky is orange, no one is going to remember that it is different. Perhaps eyes evolved on your planet such that they see in a different range of the elecromagnetic spectrum? So what. Those beings still call some wavelength red and some other wavelength green. It doesn't matter to the players since they will never really perceive it.

Same with a smaller planet. How often will the players notice the sharper curve of the horizon? Maybe the gravity is less. So people are taller, move farther with each step, and can lift larger masses. So that just means your planet has an objectively longer foot and heavier pound. Just assume it evens out in the end and while their 5-foot step would seem large to us, to people on the planet it is as it is.

 

[Nonlethal Force]

I failing to see how any of this matters.

Simple: the OP asked it to matter. The original post admits that rule zero always applies, but intentionally asked for dialogue that assumed it did matter!

I imagine your horizon would be closer on a small world, and there might be a perceptible curvature of the horizon.

Given that volume is a function of radius cubed, it depends on what the OP meant by half as small. If half meant half the radius, then this point is probably significantly important!

If the OP mean half volume, then the radius would only be smaller by a factor of the cube root of two. That's much less significant.

[Sblock=Example]To give an example, say I have a globe with a 3 foot radius. V = (4/3)(pi)(r^3). So, V = (4/3)(pi)(27), or V = 36(pi).

To backward engineer the desired radius, a globe with half the volume would have volume of 18(pi). So ...

18(pi) = (4/3)(pi)(r^3). Dividing both sides by pi gives 18 = (4/3)(r^3). Multiplying both sides by (3/4) gives ... (27/2) = r^3. In other words, r = 3/[(2^(1/3)]. r ~ 2.4.

That would probably not be a very noticable difference for the typical observer on the planet.[/Sblock]

 

[jmucchiello]

Simple: the OP asked it to matter. The original post admits that rule zero always applies, but intentionally asked for dialogue that assumed it did matter!

But who does it matter to? As I said, the players don't see the curvature of the horizon or see the color of the sky. If the planet's tilt is slightly different than Earth's, that means the sun will trace a different arc through the sky.... That means you need to place the hour markers on your sundial differently. It means shadows have different angles at 1pm than they would on Earth. But how do the players interact with that? In what way does this affect gameplay?

And the sense that things are different are only in the players' heads. For the characters, the horizon looks "normal". The shadows at 1pm are "normal". The players can compare the game world to Earth. The characters are unaware of Earth.

If the OP wants to make a world with different physics: binary stars, the planet is the moon of a gas giant, the game world is a pellucidar, the planet is flat riding on the back of 4 elephants standing on a giant space turtle, etc. that can be conveyed to the players since things will work differently. Planet size doesn't really have that kind of oomphf.