Friday, 18 December 2009

"Anatomy of an alien": high gravity






Click to enlarge (copyright BBC)









Josh said...

I've often wondered about the relationship between an increase in gravity and atmosphere density and how that would affect flight. Nice to see that i'm not the only one.

j. w. bjerk said...

I can't provide the whole answer to the gravity/atmosphere question, but maybe i can provide some information.

The relationship can't be too simple. You have for instance, substantial bodies like the moon (1/6th G) that are too light to have any atmosphere. Then at the other end you have gas giants like Jupiter with less than 3 Gs of gravity, but unbelievable crushing atmospheric pressure.

Gravity and the amount of atmosphere determine the pressure.

The amount of atmosphere is determined by how much there was to start with, how much is being added (volcanoes, comets, etc.), and how much is leaking away (which again involves gravity, and also i think temperature).

To figure out how much atmosphere was there in the first place you can either make it up, or rely on IMHO highly speculative theories of planetary formation.

I realize this doesn't really answer the question. I too would be happy if someone can provide a better one.

Dominic said...

I don't suppose you have a link to a full version of the BBC programme? Been trying to find it for ages with no luck.

Sigmund Nastrazzurro said...

Josh and J.W.:
I've asked people and am waiting for a response. my guess is that we simple have too few data to draw firm conclusions about atmospheric density and gravity, so, for 1.0 Earth gravity, anything between 0.2 and 5.0 Earth density I would believe (and wilder geuesses too, I think).

Dominic: No; I have not find a complete entry either. I'm happy to own a personal copy...

Evan Black said...

I've read Stephen Gillett's World Building and, comprehensive as the book is, it doesn't give a nice tidy formula for calculating planetary density based on other factors. It talks about air density, and even includes it in other factors, but it doesn't have anything to determine exactly what the density is and how it got that way. For my own project I've just fudged the density numbers (with a little research) to suit my needs.