From: Doug Jones (random@qnet.com)
Date: Thu Feb 17 2000 - 09:35:16 MST
Darin Sunley wrote:
>
> > James Swayze wrote:
> >
> > > A little off the subject but can someone explain to me why people promoting the
> > > terraforming of Mars still think it will hold a man made atmosphere despite the
> > > believed theory that it lost it's atmosphere in the first place due to it's
> > > diminutive size and thus lack of sufficient gravity?
>
> Well, here goes my tri-monthly de-lurk...
>
> In Greg Egan's "Diaspora", a group of post singularity aliens accomplished this
> (weighing an atmosphere down) by inserting extra neutrons into the nuclei of
> everything on the planet. One of the characters described it as "... they inserted
> the changes at the lowest level, beneath the ecosystem."
>
> Would this actually work? In other words, would Terran biochemistry (as distinguished
> from any other kind, 'natch :)) continue to work if everything was the next stable
> isotope up?
Key word: stable. Digging out the CRC handbook, I look at major
constituents of the atmosphere and lithosphere:
Element Common Heaviest
Nitrogen 14 15
Oxygen 16 18
Magnesium 24.3 26 Natural Mg is a blend of 24, 25, 26
Aluminum 27 27 No heavy, stable isotopes
Silicon 28.1 30 Natural Si is a blend of 28, 29, 30
Calcium 40.1 48
Iron 55.9 58
Just at a glance, it appears that this method would only add maybe 5% to
the mass of a planet- a lot easier just to put a lid on the atmosphere!
> More to the point, can _unmodified_ humans breathe a heavy oxygen/heavy nitrogen
> atmosphere without developing lung cancer, or asphyxiation, or similar
> unpleasantness?
Heavy water produces small but measurable effects in animal experiments;
foraminifera shift the O16:O18 ratio in their shells when the water temp
shifts (probably due to diffusion effects, not any adaptive trait).
Diffusion rates might change a bit, but the creature's overall health
shouldn't be affected.
> Furthermore, what would this do the the half-life of the atmosphere? My knowledge of
> gas behavior (does this fall under chemistry, physics, or celestial mechanics? ) is a
> little weak (CS degree). Actually, it consists almost entirely of what I've learned
> here. Say for example in the simple case, where each particle in the atmosphere is
> twice as heavy as it was before. How does this affect atmospheric dissipation rates
> due to Brownian motion and/or insufficient gravity?
>
> As a first approximation, a particle at the top of the atmosphere will dissipate if
> it exceeds the escape velocity of the planet at that altitude. The average velocity
> of all the particles in the atmosphere is simply another way of expressing the
> temperature of the atmosphere. Conclusion number one: if the atmosphere was all heavy
> atoms, the particles would move less for the same energy input, and would therefore
> be colder. (unless I'm wrongly conflating the vibration identified as heat with the
> vibration identified as Browning motion. Anybody feel free to jump in :))
Yeah, you've conflated the names, but the physics is accurate enough.
> So if the rate of dissipation of the atmosphere is proportional to the temperature of
> the atmosphere, then doubling the mass of the particles should roughly double the
> atmosphere's half-life.
I'd have to go through the complete derivation again to be sure- I think
there may be a square root or x^2 factor in there, since velocity is
proportional to the -0.5 power of molecular weight.
> Anybody feel free to tighten this up somewhat?
Ah, I have to get some real work done- I'll pass.
-- Doug Jones Rocket Plumber, XCOR Aerospace http://www.xcor-aerospace.com
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