GURPS Space - assistance

[ericthered]

Originally Posted by Brett

I see a great many. In my 10,000-star run they came in as about half of all "habitable" planets.

wow, you're getting less of those than I am. Though I am counting ALL red dwarf planets with life on them.

I like to interpret "Garden World" as meaning "organic life lives here". That doesn't actually mean much. It includes snow ball earth, several alternate biologies, and tidally locked worlds will certainly have issues. but this isn't reflected in habitability score.

[Agemegos]

Originally Posted by ericthered

wow, you're getting less of those than I am. Though I am counting ALL red dwarf planets with life on them.

I'm counting only worlds with Habitability of 5 or higher as habitable. Also, I am not counting spin:orbit resonant worlds as tide-locked. And finally, I have fiddled with the procedures for initial spin and tidal braking as discussed in the errata thread.

[Agemegos]

Originally Posted by Whill

http://www.astrobio.net/exclusive/41...‘dune’-planets-

I thought this was an interesting line of speculation regarding the likelihood and habitability of "land class" planets.

It's interesting, but I wonder how quickly the oxygen atmosphere can develop without oceans and without forests.

[David Johnston2]

Originally Posted by Brett

It's interesting, but I wonder how quickly the oxygen atmosphere can develop without oceans and without forests.

Oceans are actually a big barrier to oxygenation because they contain so much dissolved material that oxidizes. The real question (assuming that initial life can come from offworld) is how you put enough lichen down when most of the world only gets rain as a freakish occurence.

[Agemegos]

Originally Posted by David Johnston2

Oceans are actually a big barrier to oxygenation because they contain so much dissolved material that oxidizes.

Interesting. What happens to all that reduced material if it doesn't dissolve? Or do the small oceans become saturated and reduced compounds precipitate out to form thick layers of anoxic ooze?

The real question (assuming that initial life can come from offworld) is how you put enough lichen down when most of the world only gets rain as a freakish occurence.

Well, that's what I was trying to gets at about forests. If the oceans are tiny that means the great majority of the planet is arid and won't support either photosynthesis or the accumulation of fixed carbon, then the oxygen catastrophe is going to be delayed.

[David Johnston2]

Originally Posted by Brett

Interesting. What happens to all that reduced material if it doesn't dissolve? .

I'm not sure I understand the question. Most of the stuff that could become solutes doesn't because much of the planet rarely experiences rain. Instead it just remains buried underneath the oxidised surface. There's still got to be a minimum amount of surface water to maintain an oxygen atmosphere, but I'm not at all sure what percentage that minimum is.

[Agemegos]

Originally Posted by Anthony

Sure, but the key thing is that you can be in free fall without your path causing you to eventually get closer or further from either object.

Just so. And that isn't true at either the barycentre or the equipoise.

It is very common for people to confuse the Lagrange points, the barycentre, and the equipoise, and especially to give one of those that characterisation of one of the others. It's worth keeping them straight, I think.

[Whill]

Would it be possible for an Earth-mass world to stay in a Lagrange point of a star and a very massive gas giant?

[Agemegos]

Originally Posted by Whill

Would it be possible for an Earth-mass world to stay in a Lagrange point of a star and a very massive gas giant?

L4 or L5, yes. L1, L2, or L3, no. The gas giant has to be at least about 25 times the mass of the terrestrial.

In the context of a planet orbiting a star, these trajectories are also called the leading and trailing Trojan points.

[Whill]

Originally Posted by Brett

L4 or L5, yes. L1, L2, or L3, no. The gas giant has to be at least about 25 times the mass of the terrestrial.

In the context of a planet orbiting a star, these trajectories are also called the leading and trailing Trojan points.

Thanks. Would there be any severe radiation or other habitability complications with a terrestrial planet at L4 or L5 when the gas giant is 4000 earth masses?