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).
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.
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
Only if solar wind can be modeled by a uniform field. Radiation from flares might not drop off in an inverse squared relationship, but I'm not an astrophysicist so this is just speculation.
Flares shouldn‘t be uniform, but I‘m doubting that they‘d disturb a terraformed Martian ecosystem much as they are quite rare. I‘m guessing some moderate EM hardening of electronics would be enough. As we should have here btw., the next one-in-200y flare is not going to be pretty.
Solar flare particles (unlike cosmic rays) are rather low energy, so it doesn’t take much to shield from them. I believe the surface of Mars is reasonably safe due to its atmosphere. Even at 0.007 atm, the total mass of air between you and the sun is quite large.
Solar flare particles would be an issue on the journey to Mars, however.
For cosmic rays, the exposure on Mars is the same as on the ISS: half that of deep space (the other half blocked by the planet below you). But so far there hasn’t been an elevated cancer rate for ISS astronauts, many of whom have spent 6+ months there.
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.
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.
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.
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.
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.
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.
