
Why is only half of Mars magnetized? - grey-area
http://www.planetary.org/blogs/emily-lakdawalla/2008/1710.html
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BWStearns
Does this indicate that half of mars has useful enough magnetism to shield it
from solar radiation for human habitation purposes? (I honestly don't know the
answer or how to discern it from google).

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mirimir
The field is only 2.5% of Earth's. That's way too weak, I suspect.

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BWStearns
Thanks for the reply. Any idea if it is even a meaningfully better
neighborhood magnetically than the northern hemisphere?

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tritium
To gather something that seems like a reasonable answer, you’d have to
consider that while Earth’s magnetic field deflects charged particles from the
solar wind, the atmosphere is also an important deflector and buffer for the
absorption of other forms ionizing radiation, so even if the magnetic field
deflects charged particles, like free protons, free electrons and alpha
particles, there’s still the occasional burst of X-rays, neutrinos and the
constant UV radiation and probably even some neutrons, which mostly gets
caught by the air and distributed into the environment as heat.

So, the comparatively thin Martian atmosphere is probably a bigger deal than
the magnetic field, generally speaking.

Anyway, to approximate how big a deal this all is, you’d have to consider the
inverse square law, to account for how much weaker the intensity of the
radiation is, given that Mars is farther from the sun than Earth is. If Earth
is roughly one astronomical unit from the sun, Mars is about 1.52 units away.
The inverse square law says that as the distance doubles, the signal strength
is four times weaker, triple distance weakens strength by nine times. So,
1.52^2 is ~2.3104 times weaker intensity, which is partly a correlation to the
disk of the sun being visibly smaller, farther away.

If the general, overall radiation is at least twice as weak, or more than 50%
weaker on Mars, the strength of the Martian magnetic field being 98% weaker
than on Earth, probably means it’d still need to be 49 times stronger than it
is to effectively deflect an amount proportional to the solar wind which is
deflected by Earth. This means that on the surface of Mars, 50 times the
amount of solar wind still rains down into the thin atmosphere, and much of it
is still probably scattered by the air as heat, instead of forming into a
Martian Van Allen belt.

During solar storms, however, when solar radiation is emitted at higher
levels, it could be a bigger deal. I think much of the particles falling onto
Mars would simply ionize in the air overhead before reaching the surface (as
static electrical effects, like lightning or aurora plasma), but flare-ups of
sun weather could easily be a real problem, since they still are problems even
here on Earth.

The fact that you can see a sky on Mars during the day means that the air
overhead is doing some work scattering the inbound sunlight, even if the sky
isn’t blue. The atmosphere is about 10 kilometers thick, and air pressure is
weak enough to boil water at room temperature (less than 1% of standard good-
weather air pressure on earth). So, the barely-there atmosphere ensures that
skin cancer and penetrating rays aren’t a super big deal, because moreso than
providing natural barriers itself, the Martian environment ensures people will
pretty much always be in thick suits and behind thick windows and walls as a
pervasive fact of life.

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raamdev
Thank you. I wish more textbooks read like this!

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yorwba
What do textbooks usually read like to you?

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pokemongoaway
Like your comment ;P

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yorwba
I was actually interested in a serious answer, since I don't tend to need to
read textbooks.

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troylinn
I find learning from textbooks is more difficult then learning in an open
forum discussion or not confined to the strict teachings usually provided by
textbooks

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perl4ever
The article says so many things are explained about _Mars_ , but now I am
wondering why the same thing didn't happen to _Earth 's_ magnetic field, if
there was a giant impactor, and why Mars doesn't have a large moon, if _it_
had a giant impactor.

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kuschku
The article explains the size differences very well.

And it mentions that mars' impactor only remelted half the surface, while
earth's impactor melted the entire surface of the planet. Which is supposedly
why earth's magnetic field stayed axially dipolar.

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perl4ever
From what I've read, the size, speed, and angle of whatever hit the earth is
not settled. But if we know that, as you say, half of Mars was melted, while
all of Earth was melted, then that should put constraints on how the impacts
differed, which is what I was curious about and is not part of the article.

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labster
Without knowing all that much, I know that Earth was much more massive than
Mars even before Theia impacted. I assume with the extra energy available, it
would be much more likely to melt all the crust. Also, our plate tectonics is
still going on, so any evidence of a thin area of crust would be erased by
now.

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Zardoz84
also it's interesting that the crust of the moon have differences between far
and near side. I read somewhere that this could be explained very easily with
a low speed impact of a second small moon when the moon was very young.

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perl4ever
There was a recent paper proposing that the near side of the moon looks melted
because the surface of the Earth was temporarily about as bright as the sun
for a while after the impact.

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elnurmen
Both Earth and Mars hit by giant impactors on a __sliding __trajectory? Seems
fishy!

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orbital-decay
A direct impact is actually less probable than a sliding hit.

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thriftwy
I wonder how can half a planet be low-lying without reconsidering the zero of
such measurements?

Same thing for high half. Maybe just agree that Mars is located one mile
further, high half direction?

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the8472
center of mass != geometric center

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Iwan-Zotow
Y'all know how it happens - unclear specs, lousy pay, outsourcing to India

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JoelMcCracken
At first I thought this said "monetized". Which, I think, is an interesting
comment on the state of the world, or at least my perceptions of them.

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cvaidya1986
My theory is that the martians built their anti magnetic machine and buried it
deep near the Martian core. They themselves live in deep underground colonies
near mines where they can find precious metals and water.

