Smaller Planets

[BRP2]

I was wondering. I want to make a campaign setting where the world is smaller than Earth, by a decent amount(maybe as much as half as small). I'd like it if everything else remained the same though. The year, the day, one moon, four seasons, ect ect.

Now, I know I can Rule 0 in anything I want, but I'm curious now. What would be the effects of a smaller planet(without Rule 0)?

 

[hong]

We'd all be jumping really high. And suffocating, but that's not much fun so don't worry about it.

 

[BRP2]

Ah, gravity.

Anyway, I just noticed Rogues' Gallery has been renamed and now includes "Places". Mod might wanna move this there.

 

[Delta]

I do this in my campaign world. Per real-world physics, there has to be a deposit of some super-dense material at the center of the planet. (Probably there's some subtle complications but that's what I do.)

 

[Peni Griffin]

There's plenty of reference and popular science books in the astronomy, geology, and physics sections to help you, but the book you want for inspiration is The Wonderful Flight to the Mushroom Planet, and its sequels, by Eleanor Cameron.

http://www.fantasticfiction.co.uk/c/eleanor-cameron/wonderful-flight-to-mushroom-planet.htm

1954. Backyard rocket. Little green men. Suspend your disbelief by the neck until it's dead and have a ball.

 

[Aust Diamondew]

Physics are over rated, after all my D&D world is flat.

Its possible creatures would have evolved/created with lower strength scores as with less gravity higher strength wouldn't be as necessary. On the other hand having a higher strength score would still be useful for the uber jumpings.

 

[Nonlethal Force]

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.

As far as length of day, that involves rotational velocity. In other words, how long does it take to spin around. The thing is, size does not matter. Think of a record or a CD. One revolution is one revolution regardless of the size. The thing that will get your mind in a twist is to realize that while the planet will be spinning with the same rotational velocity, the people on the surface of a bigger planet will be spinning around significantly faster than the people on the smaller planet in order to make the same number of revolutions (because the larger planet means they have farther to go, of course!). But, as far as in game effects that should be able to be ignored by all but the biggest of science geeks like me!

Seasons are dependent upon the tilt of the planets spin ... also called the axis of rotation. That should be able to be the same.

One moon should be able to be the same. If your ground is the same mass (thus more dense to compensate for less matter) ... the moon could easily be exactly the same as earth's and in the same position so as to have the same tidal effects. If you want a closer moon (and thus bigger in the sky), it would either have to be made of less dense material or be smaller to have the same tidal effect. If you want a farther moon (and thus smaller in the sky) it would have to be more dense or larger to have the same tidal effects.

I think I got all that right. If not ... well, the advice was free!

 

[dougmander]

Go here .

 

[Sir Brennen]

I do this in my campaign world. Per real-world physics, there has to be a deposit of some super-dense material at the center of the planet. (Probably there's some subtle complications but that's what I do.)

A world with a molten adamantine-core instead of iron/nickle. Now there's a thought...

 

[BRP2]

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?