Originally posted by Metal Brain
Gravity is not always the determining factor for a thick atmosphere being on a planet or moon, it is also a magnetic field.

http://www.popularmechanics.com/science/space/moon-mars/what-happened-to-mars-atmosphere-15277534

Europa (Jupiter's natural satellite) is slightly smaller than the Moon, but it has an atmosphere (and might have water beneath /features/magnetic-fields-europa.php

http://www.bbc.co.uk/news/science-environment-15754786

you are, of course, correct.

Europa is also colder and a lot further from the sun. Both of those things would make it easier for it to maintain an atmosphere.

Being further from the sun means, if you ignore any extra protective effect of a magnetic field because that complicates the picture, the solar wind striking its outer atmosphere would be less strong and thus would tend to sweep away its outer atmospheric molecules and ions to outer space at a slower rate.

A magnetic field, of course, gives extra protection from atmosphere being lost to outer space because it tends to deflect the solar wind from striking it.

being colder helps providing this means the outer most atmosphere is colder because that would then mean that the average kinetic energy and therefore the average speed of the gas particles and ions in its outer most atmosphere would be less and thus, at any given moment of time, less of them would be at escape velocity. This would reduce the rate of atmosphere being lost to the vacuum of outer space.

Originally posted by sonhouse
Speaking of magnetic fields, I was thinking about the problem of Mars not having much in the way of magnetic fields, some local ones but not enough to shield the planet. So I'm thinking, if and when we get room temperature + superconductors, would it be possible to bury that cable around the equator of Mars and start a current flowing, powered by a huge sol ...[text shortened]... kilometers in circumference. (13340 miles)

That is roughly half the circumference of Earth.

I don't know how to calculated that but I would guess the current would have to be immense! I think the strength near such cables would have to be so strong that it could cause serious health and safety issues to any possible human inhabitants that would colonized Mars. And this not even to mention the safely issue of magnetic quenching that could cause it to suddenly all fail and explode! Pity, because I think that is an interesting idea.

Originally posted by humy
I don't know how to calculated that but I would guess the current would have to be immense! I think the strength near such cables would have to be so strong that it could cause serious health and safety issues to any possible human inhabitants that would colonized Mars. And this not even to mention the safely issue of magnetic quenching that could cause it to suddenly all fail and explode! Pity, because I think that is an interesting idea.

You are only going for field strength of a Gauss or so. I think I did the calc before. The thing about quenching fields is they have designs that use superconductors as energy storage devices and they have to account for field quenching if something happens, break in the line, temperature too high, whatever, they get around that by putting a mass of copper in parallel but for a 20,000 km cable that might be a bit expensive. It might be cheaper just to build two separated by a km or so and if one blows, you switch to the other. Redundancy.

I found this site that calculates the force in Gauss:

http://hyperphysics.phy-astr.gsu.edu/hbase/magnetic/curloo.html#c2

It looks like a single turn of about 20,000 km with 100 million amps flowing would produce a field of 0.06 Gauss. If that were the case then 1000 turns with 1 million amps would produce the same field. Don't know if that would be strong enough, the Earth's field is ten times that.

If those numbers are right, I guess it is a hairbrained idea. Don't know how big a superconductor cable it would take to be able to take 100 million amps but it sounds like it would be pretty big around. Oh well, maybe in a couple hundred years....

I know they talk about magnetic shields on a smaller scale, a few miles across to protect a town but don't know the current requirements.

You want to check out the site and see if what I found is correct?

Originally posted by sonhouse
You are only going for field strength of a Gauss or so. I think I did the calc before. The thing about quenching fields is they have designs that use superconductors as energy storage devices and they have to account for field quenching if something happens, break in the line, temperature too high, whatever, they get around that by putting a mass of copper current requirements.

You want to check out the site and see if what I found is correct?

Wait! I have just thought of a way around this safety problem!
Instead of having cables encircling the whole planet, why not have millions or billions of small separate superconducting magnets evenly spaced over the whole planet and with all there magnetic north poles pointed in the same direction!
You could also have each one of them positioned in its own deep underground chambers so that if one blows up due to magnetic quenching, no damage would be done to anything on the surface of the planet and also the shock-wave and shrapnel would not cause the nearest superconducting magnets to also blow up. But I would guess that you would have to have them very deep though to stop their local magnetic field causing a health and safety issue to people on the surface. My best intuitive guess is that you need to make them at least 4 kilometers deep but that partly depends on the size of each one.

Originally posted by humy
Wait! I have just thought of a way around this safety problem!
Instead of having cables encircling the whole planet, why not have millions or billions of small separate superconducting magnets evenly spaced over the whole planet and with all there magnetic north poles pointed in the same direction!
You could also have each one of them positioned in its own ...[text shortened]... ou need to make them at least 4 kilometers deep but that partly depends on the size of each one.

BTW, I entered the wrong numbers into the strength calculator, I put in the circumference rather than the radius, which is 6 times larger. I will go back and feed the proper number to see what pops up. My guess is the answer will go from 0.06 Gauss to 0.36 Gauss. Rather a better number from a shield POV. I also thought of variations on the main theme. You could use multiple loops but instead of a very long one at the equator, you could put several much smaller loops closer to the poles, say where the radius is a couple hundred km rather than the roughly 1800 km of a loop at the equator.

I think the gist of all this is in the future if and when they finally get real colonists and start thinking in terms of terraforming Mars, there will be magnetic systems in place that will give the planet the shield that will in effect keep in the atmosphere by keeping out the solar wind.

It sounds to me like a technology issue not a fundamental deal breaker.

One thing that is clear however.

If you had some kind of superconducting loop magnets and so forth, however it would be implemented, the variation in the strength of the solar wind, quite days vs days during a coronal blast that hits Mars, the solar wind would interact with the magnetic field in such a way as to lower the strength of the field, which would require a feedback network to feed energy back into the field to restore the shield. I don't think the field strength would recover without an additional input of electrical energy because I think the field strength would go up and down on a daily basis due to variations in the solar wind intensity.

Originally posted by sonhouse
BTW, I entered the wrong numbers into the strength calculator, I put in the circumference rather than the radius, which is 6 times larger. I will go back and feed the proper number to see what pops up. My guess is the answer will go from 0.06 Gauss to 0.36 Gauss. Rather a better number from a shield POV. I also thought of variations on the main theme. You c d strength would go up and down on a daily basis due to variations in the solar wind intensity.

but why have any unwieldy large loops at all when you can produce the same strength of magnetic field over the whole planet using a great many separate small superconducting magnets (each one being, say, just ten meters across) evenly spaced all over the planet so that all those magnetic field join up to make one big magnetic field that covers the whole planet? I think this would be a much more practical in comparison albeit still not necessarily actually practical.

Originally posted by humy
but why have any unwieldy large loops at all when you can produce the same strength of magnetic field over the whole planet using a great many separate small superconducting magnets (each one being, say, just ten meters across) evenly spaced all over the planet so that all those magnetic field join up to make one big magnetic field that covers the whole planet? ...[text shortened]... is would be a much more practical in comparison albeit still not necessarily actually practical.

If you guys would stick to practical science, then you would not need someone to point out your speculations by giving counter speculations.

The Instructor

Originally posted by RJHinds
If you guys would stick to practical science, then you would not need someone to point out your speculations by giving counter speculations.

The Instructor

Somebody has to do the grunt work speculations or nothing would ever be invented, but you don't know about that kind of thing, with your self lobotomized brain. The payoff for recreating a magnetic field on Mars is to basically give us another planet. As it stands now, yes we can reach Mars and so forth but as a planet it sucks. No shield from the solar wind, which slams right down to the surface on a bad day so people would be living in caves till someone comes up with a practical magnetic shield.

Meanwhile you can go on trying in vain to keep on proving the Earth is only 6000 years old and there you will be permanently stuck in a rut of your own making. You have no-one to blame for that rut but yourself.

Originally posted by sonhouse
Somebody has to do the grunt work speculations or nothing would ever be invented, but you don't know about that kind of thing, with your self lobotomized brain. The payoff for recreating a magnetic field on Mars is to basically give us another planet. As it stands now, yes we can reach Mars and so forth but as a planet it sucks. No shield from the solar win ...[text shortened]... manently stuck in a rut of your own making. You have no-one to blame for that rut but yourself.

I think technologies for interstellar space travel is more likely to be developed than giving mars a magnetic shield. If we could use either anti matter or nuclear fusion or fission it seems that the mass of the fuel would increase as we approach the speed of light. Since the power is mass dependent I should think in this case it would work to our favor. If you and hinds were to get aboard a ship that has a rotating cylinder to simulate gravity and travel many many light years to a habitable planet, you guys would still not agree and the age of the earth.

Originally posted by joe beyser
I think technologies for interstellar space travel is more likely to be developed than giving mars a magnetic shield. If we could use either anti matter or nuclear fusion or fission it seems that the mass of the fuel would increase as we approach the speed of light. Since the power is mass dependent I should think in this case it would work to our favor. ...[text shortened]... many light years to a habitable planet, you guys would still not agree and the age of the earth.

More like the universe vs hinds would not agree on the age of the Earth.

But Mars is here and now, a living planet we are exploring as we speak so we WILL be going there some time in the near future. The problem with interstellar travel is you either go at 0.99c or you live on a generation ship where it takes 300 years to get to anyplace nearby in interstellar space.

Another problem is we have very few candidates that would show planets in the goldilocks zone where liquid water can exist.

Me, I would go immediately to Alpha Centauri because it is a three for one voyage, 3 stars within 1/10th of a light year from one another so it triples the chances of finding a nice Earth-like planet. But that is just me.

I think going to Alpha Centauri would be a great voyage even if there were no Earth-like planets for many scientific reasons, one being the base for doing astronomy would now be 4 light years across instead of the maximum of 180 odd million miles across that we now get for stellar parallax studies so simply BEING there would greatly increase our knowledge of interstellar distances. That is just one advantage that comes to mind about visiting Alpha Centauri.

Of course, interstellar voyages cannot be contemplated in THIS century, perhaps in century 22 or 23. I could be wrong but I don't think the political will would be there to contemplate such a voyage since we are sputtering along barely staying afloat financially in the world economy.

I don't think there is going to be anything like an economic boom in the next 50 years and so really big projects like interstellar travel and fusion or fission or anti-matter propulsion systems are unlikely to be built in century 21.

Or the even further out proposals for wormhole transport and such.

Anti-matter may turn out to be the best bet for propulsion since there are schemes afoot that can capture interplanetary anti-matter already in existence, since the universe has decreed anti-matter can exist at a ratio of about 1 in ten billion so one out of every ten billion atoms is anti-matter which means there is a LOT of it right here floating around in the solar system so if we develop means to capture existing anti-matter, it will be a slam dunk to make anti-matter rockets. The designs are already there for anti-matter rockets.

All we need is anti-matter in gram quantities and we will have interstellar propulsion systems.

But I don't think any of those schemes will be done in century 21.

Originally posted by RJHinds
If you guys would stick to practical science, then you would not need someone to point out your speculations by giving counter speculations.

The Instructor

How would you know it could not ever be 'practical' science? You are completely ignorant of science and have already proved to be totally incapable of understanding any of it. You don't have the slightest idea what it is about so any opinionated criticism you make of it here is purely based on pure ignorance, religious extremist dogma, hatred of anything rational like science, and stupidity.

Originally posted by humy
How would you know it could not ever be 'practical' science? You are completely ignorant of science and have already proved to be totally incapable of understanding any of it. You don't have the slightest idea what it is about so any opinionated criticism you make of it here is purely based on pure ignorance, religious extremist dogma, hatred of anything rational like science, and stupidity.

You are an atheist because you have been indoctrinated by propaganda on false science.

The Instructor

Originally posted by RJHinds
You are an atheist because you have been indoctrinated by propaganda on false science.

The Instructor

You are a troll because you have been indoctrinated by propaganda on false religion.

Originally posted by sonhouse
You are a troll because you have been indoctrinated by propaganda on false religion.

No, mine is the true religion.

The Instructor

Originally posted by RJHinds
No, mine is the true religion.

The Instructor

That's what they ALL say. No street cred.