How little gravity before it is considered microgravity (for using Athletics vs. Free Fall skills)?

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ICU2 ICU2's picture
How little gravity before it is considered microgravity (for using Athletics vs. Free Fall skills)?

How little of gravity before Athletics gives way to Free Fall? Is there a defined border? Would it be reasonable to set one? Is anything with less than 0.1 g microgravity for game purposes, or perhaps less than 0.01 g?

Venus (0.9 g), Mars (0.38 g), Mercury (0.377 g), Luna (0.165 g), Titan (0.138 g), and Europa (0.134 g) all seem like they have enough gravity for Athletics to be the skill dictating movement.

What about Ceres (0.029 g)? It's the lowest surface gravity of significant named objects that I can find. Is 3% of Earth's gravity enough that Athletics would be used, or would this be treated as a microgravity environment requiring Free Fall?

chaos_forge chaos_forge's picture
There's not a hard boundary

There's not a hard boundary defined AFAIK. The books says "These conditions are found in space, on asteroids and some small moons." So most moons in the solar system would not be in microgravity, it seems. Ceres has a similar gravity to a medium-sized moon, so I'd say it's probably not in microgravity.

A decent place to draw the line IMO is whether or not a body has enough gravity to reach hydrostatic equilibrium and become rounded due to its own gravity. Looking at this list of gravitationally rounded bodies in the solar system, it seems the lowest surface gravities among them are Miranda, with a surface gravity of 0.008 g, and Mimas, with a surface gravity of 0.006 g.

So if we wanted to say that a body is microgravitating if it doesn't have enough mass to become rounded from its own mass, we could say microgravity is <0.5% of Earth gravity. I could also consider drawing it at <1% of Earth gravity, both to have a nice round number and to capture the fact that the book mentions "some small moons" being in microgravity as well.

ICU2 ICU2's picture
Thank you. Those values seem

Thank you. Those values seem reasonable enough to work with.

chaos_forge chaos_forge's picture
No problem! Another option is

No problem! Another option is embracing the fuzzy boundary and saying that, on worlds that have, say, between 0.05g and 0.01g surface gravity, players can choose whether they want to use freefall or athletics to get around.

ICU2 ICU2's picture
chaos_forge wrote:No problem!

chaos_forge wrote:
No problem! Another option is embracing the fuzzy boundary and saying that, on worlds that have, say, between 0.05g and 0.01g surface gravity, players can choose whether they want to use freefall or athletics to get around.

I think you mean 0.005 g and 0.01 g, right?

I know that Extropia (44-Nysa) is supposed to be a microgravity environment, and it has approximately 0.002 g.

chaos_forge chaos_forge's picture
ICU2 wrote:I think you mean 0

ICU2 wrote:
I think you mean 0.005 g and 0.01 g, right?

I was taking anything <0.01g as being exclusively freefall. I chose between 0.05g and 0.01g as the fuzzy zone so places like Ceres would be included in it, since it's fairly easy to imagine someone moving "freefall style" in a place where they weigh 5% of their Earth weight, but at the same time there's still enough gravity that if you drop yourself you'll hit the ground in a reasonable amount of time.

Hydrargyrum Hydrargyrum's picture
Here's an intuitive rule-of-thumb that works for me

How's this for a guideline:

If you jump and land back on the ground within the same action turn, it's Athletics.

If you jump and never land (because you achieved escape velocity from your local gravity well), it's Freefall.

If you do land (i.e. jumping doesn't achieve escape velocity) but it takes more than one turn to complete the arc, then you can pick which one you want to use. Particularly brutal-feeling GMs might ask you to roll against the lowest of the two skills!

Hydrostatic equilibrium is a pretty handy guideline to use because it's pretty easy to tell from looking at a picture of a celestial body whether it meets the threshold or not.

ICU2 ICU2's picture
Page 63 of Gatecrashing says:

Page 63 of Gatecrashing says: "Oberon has a surface gravity of 0.035, making it a microgravity environment."

This would definitely put Ceres (0.029) into the microgravity range too, but I'm not sure how much it increases the upper range of microgravity. I could probably go with < 0.05 as the boundary.