Not that I WANT to terraform Mars...

From: Dr. Omni [mailto:dromni@...]

Uh, I've heard Martians talking about giving a 1/3 *bar* atmosphere to Mars.
That means an atmosphere exerting 1/3 of the atmospheric pressure of Earth
at sea level. Since the Martian gravity is around 1/3 g, then in fact you
would have to have a column of air with 10 metric tones of mass above each
square meter of the Martian surface - the same value on Earth. So, although
exerting less pressure, this atmosphere would provide as much passive
shielding as Earth's, because cosmic rays would have to pass through 10
tones of air in either planet. Or am I missing something?

Ah. Thanks for making an important distinction here.

What I didn't appreciate until now was that when the Mars terraformers
proposed a 1/3 bar atmosphere for Mars, they were still having to talk about
making just as much air per square meter as covers the Earth. I'll bet many
Mars advocates, like myself, considered a 1/3 bar atmosphere for Mars an
easier proposition than it really is, mistakenly assuming much less air
would be needed.

It then seems to follow that in order to get a totally Earthlike Mars (one
where people can live out in the open and not just under Saran-wrapped
cities with greatly enhanced O2 percentages) will require around 3 times as
much air per square meter than is the case for Earth. Things keep getting
more difficult...

Even if the passive atmospheric shielding is really not enough, I think that
a terraformer could argue that a radioactive surface is not exactly an
unsolvable problem. People could live in underground houses and so get
exposed to cosmic rays only during brief periods of time (after all, most
people spend the vast majority of their time indoors).

If they did make this argument, I think it would be a very poor one. Living
underground even after terraformation is certainly not what most people are
visualizing when considering the concept.

Regards,

Mike Combs

From:
Dr. Omni [mailto:dromni@...]

Uh, I've heard Martians talking about giving a 1/3 *bar* atmosphere to Mars.
That means an atmosphere exerting 1/3 of the atmospheric pressure of Earth
at sea level. Since the Martian gravity is around 1/3 g, then in fact you
would have to have a column of air with 10 metric tones of mass above each
square meter of the Martian surface - the same value on Earth. So, although
exerting less pressure, this atmosphere would provide as much passive
shielding as Earth's, because cosmic rays would have to pass through 10
tones of air in either planet. Or am I missing something?

Ah. Thanks for making an important distinction here.

What I didn't appreciate until now was that when the Mars terraformers proposed a 1/3 bar atmosphere for Mars, they were still having to talk about making just as much air per square meter as covers the Earth. I'll bet many Mars advocates, like myself, considered a 1/3 bar atmosphere for Mars an easier proposition than it really is, mistakenly assuming much less air would be needed.

It then seems to follow that in order to get a totally Earthlike Mars (one where people can live out in the open and not just under Saran-wrapped cities with greatly enhanced O2 percentages) will require around 3 times as much air per square meter than is the case for Earth. Things keep getting more difficult...
Even if the passive atmospheric shielding is really not enough, I think that
a terraformer could argue that a radioactive surface is not exactly an
unsolvable problem. People could live in underground houses and so get
exposed to cosmic rays only during brief periods of time (after all, most
people spend the vast majority of their time indoors).

If they did make this argument, I think it would be a very poor one. Living underground even after terraformation is certainly not what most people are visualizing when considering the concept.

Regards,
Mike Combs