GURPS Space - assistance

[Agemegos]

Originally Posted by Whill

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?

No. A gaseous body of 4,000 Earth-masses is getting on for being a brown dwarf rather than a gas giant, but L4 and L5 are just as far from the planet as they are from the star, so any radiation hazard from the planet will be dwarfed by that from the star.

[Agemegos]

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.

Sorry, there is a limit but that's not the right one. That's the limit on the ratio of the masses of the star and gas giant.

[Fred Brackin]

Originally Posted by Brett

No. A gaseous body of 4,000 Earth-masses is getting on for being a brown dwarf rather than a gas giant, but L4 and L5 are just as far from the planet as they are from the star, so any radiation hazard from the planet will be dwarfed by that from the star.

Yeah, you've got an extremely large super-Jupiter but even if its' magnetosphere is in proportion to its; mass (c.12x Jupiter) L4 or 5 would be about 1 AU away. The radiation belts won't stretch that far.

The Earth-type planet might still need a largish moon of its' own to avoid tidal locking or at least length of day issues.