Re: Building a map of habitable space

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RBW said:

"Somewhere between the two is another possibility: borderline-habitable
planets become regarded as "habitable" for lack of a decent alternative.
Sure, you have to stay in sealed buildings or wear a mask to scrub out
(most of) the sulphur dioxide, but once you get used to the smell it's
fine..."

[Tomb] My definition of habitable was 'things which are going to be
habitable by humans using available technologies of the day'. This would
include your borderline habitable worlds.

I don't see us living on exoplanets with G ratings below 0.5
successfully.
Zero G and probably low-G as well does some awful things to our immune
systems and bones. Similarly, anything over about 1.2 Gs strikes me as
unlikely as well. You could try to run grav plates full time, but the
energy consumption would presumably be silly and this posits
gravitational
control which may remain permanently elusive. And if the power went out?

But also temperatures of 2290 K or 4000 K seem likely to deter us.

The need for 12 essential vitamins (or the in other words, a collection
of
necessary inorganic but also organic materials) in our diet means that
many
places may not have key human-necessary nutritional elements. It's fine
to
talk about supplementing diet at small research stations but not of a
world
sized population; They would have to be able to produce the necessary
compounds themselves.

Then we'll talk about things like partial pressures of gasses in the
atmosphere, absence of allergens or poisons like heavy metals, etc.

Habitable I think will *always* mean marginally habitable, even with
allegedly 'Earth like' worlds. I could be wrong, but so far I see no
reason
to believe there is a planet out there with the right:
a) atmospheric gas mix
b) amount and type of cosmic radiation arriving (and proper amount
bouncing
off or being absorbed)
c) habitable temperatures
d) partial pressures in the atmosphere
e) gravitation
f) presence of all necessary nutrients
h) lack of poisons or other compounds inimical to life

Some of these, tech may help us work around, thus turning 'not really
habitable' into 'yeah, we can live there in domes or whatever'. Some,
not
so simple to compensate for.

I don't see an Earth 2 anywhere handy.

T.

PS - Economics? My condolences. That's almost as bad as Computer
Science.