Re: Help with worldbuilding

Logan Kearsley wrote:

> Removing/smallifying the nickel-iron core would probably help a lot

That's a good thought (kind of a "reverse Mercury" situation). I'm
still unclear on how low you could go, but this is a good way to get
there (or at least move in that direction).

> [on retaining an atmosphere[ you ought to be able to just
> barely get by with 1/30 of an Earth mass and still hold on to a
> nitrogen/oxygen atmosphere at the same density as Earth
> and a Venus-like exosphere

One more caution on all this - while for rasfs discussions assuming
"Jeans escape" of the atmosphere is OK, if you want to be accurate,
there are a lot of other ways to loose an atmosphere, including solar
wind stripping and even chemical reactions. For instance, thermal Jeans
escape can acccount for only about 3% of the He escape rate measured on
Earth. For He, collisions between ionized He & atomic O fire off He at
high velocity.
OK, enough of piling wood on the bonfire ;-).

> [photosynthesis] maybe concentrating the energy derived
> from multiple quanta of far red light to do what one quantum
> of blue light could do

Yes. Actually, terrestrial photosynthesis already does this. But
it's not as efficient, in that "two reds make a blue-&-a-half, but the
downstream system only uses a blue-&-a-quarter". In other words, more
energy is potentially "wasted" by multi-photon systems, but if you
weren't using those photons to begin with... it all depends on how you
define "efficiency" here. My original point was that photosynthesis is
already terribly inefficient, and yet it's not gotten any better,
suggesting (to me) that it's a hard system to optimize.
Which is not saying a completely novel system might not have these
these problems.

> Or, if the pigments they use are sufficiently versatile
> and easily tunable (like the proteins in eyes, perhaps?)

I *think* the eye works with filter pigments, not "tunable
photosystems", but I really don't know; anyone? Note there is at least
one photosystem (*not* photosynthesis... yet) that does not use
Chlorophyll. There is at least one halobacteria that has apparently
evolved a novel photosystem based on, yep, you guessed it,
bacteriorhodopsin, using essentially the same pigment (retinal) that is
in the eye. It's absorption peak is at 572 nm (in the green portion of
the spectrum), and the membrane looks purple. The system is about six
times "weaker" than the two chloropyhll-based system, but it does work.

--
Brian Davis

.

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