Before diving into these questions let's go over a little physical background. A common belief is that Mars lost its atmosphere either because it was not massive enough to hold on to it (and thus thermal escape dominated), or that it was stripped away by solar wind.
The reality is that Mars lost its atmosphere by a mixture of these and other processes all acting together. Mars is light enough for hydrogen and helium to readily escape thermally. This combined with photodissociation of water also explains why Mars is so red. The Sun's ultraviolet let dissociated the water into hydrogen and oxygen, and the hydrogen escaped while the oxygen reacted with the rocks to form iron oxides.
Another important mechanism for the loss of the Martian atmosphere was impact erosion
. In the early solar system, impacts were big and frequent enough to eject significant portions of the atmosphere to space.
Finally there is sputtering by solar wind directly impacting the atmosphere, which a magnetic field would help reduce. A planetary magnetic field does not completely prevent this loss however, since near the poles the magnetic field lines do not close around on themselves, so accelerated ions can flow along them and escape into space, producing a "polar wind". This is an important mechanism for the loss of hydrogen and helium from Earth.
There are still other escape mechanisms for atmospheres, but for Mars these are the big ones. With this in mind, let's look ahead to this idea of protecting Mars with a magnetic field generated remotely:
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1) How powerful would this generator and its field need to be for most of Mars to be in a 0.5 to 1.0 Gauss range? (Similar to Earth's, right?)
All magnetic fields essentially arise from currents, or moving charges. For starters, let's imagine the magnetic field generator to be a simple current loop. The magnetic field along the axis of a current loop is given by
At large distances perpendicular to that axis, the magnetic field is roughly half as strong, so for our purposes the exact geometry of the field is fairly irrelevant to an order of magnitude calculation.
How far must this magnetic field reach in order to protect Mars? The Martian L1 Lagrange point lies about .0072AU (1.08 million km) in the direction of the Sun:
Going back to the formula and rearranging it to be slightly more convenient (and dropping a factor of 2 to get the long range equatorial field strength), we can find the amount of current needed in a loop of radius R to cause a field of strength B at a distance z, which we'll set to 0.0072AU.
At large distances (z>>R), the required current to produce a field B is proportional to B/R2
. So a larger ring is better to minimize the current needed. How much current?
Oh boy... If the ring at L1 is 1000km across, then we need a current of about 1018 Amps, to enclose Mars in a 1 Gauss field.
Amps is a lot
of current. Now I have not accounted for the fact that the solar wind will distort the shape of the field, as you mentioned, so perhaps this reduces the requirements a little. But computing that effect is complicated, and I don't think it would change the answer enough to matter anyway. Perhaps this also raises the question, "How do planets generate such wide fields?" The answer is that planets are very big, so the actual current density circulating around in them can be quite small.
So I think the short answer to this question is, "to make a magnetic field like a planet, you basically need something like a planet"
Exotic objects like neutron stars of course have very
strong magnetic fields, but this is because they have much higher current densities.
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3) Can this be done with current technologies? And what might the object itself look like?
With today's technology it seems difficult at best. We would probably need to use a superconducting ring thousands of kilometers in scale. An even deeper problem is how strong the magnetic field must be close to this generator, if we put it at L1, in order to have the required strength at Mars' location. Using the 1000km wide ring with 1018
Amps, the field at 100,000km will exceed 1 Tesla, and close to the ring itself it will exceed 100,000 Tesla! People, ships, infrastructure, electronic components and so forth anywhere near this thing will need to use very good magnetic shielding.
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4) Given Mars' current natural processes and environment, would the atmosphere start to build itself up, given the above Gauss range?
Probably not. Mars is not outgassing very much anymore. Its opportunity for building up any appreciable atmosphere was in the past.
The most significant atmospheric process now is a seasonal variation in the CO2 pressure, as the ice caps sublimate and refreeze. There are also some trace emissions of methane, but this is in the few parts per billion range, and it quickly gets sequestered again in the rocks. In general the current Martian atmosphere simply cycles between air and ground, with a slow steady loss to space by the various atmospheric escape mechanisms. To give Mars any appreciable atmosphere we would need to take more direct measures to build it up.If we did that, then the loss rate for heavy atoms (nitrogen, oxygen, etc) is slow enough that we wouldn't need to worry too much about protecting it with a magnetic field, at least in the short term. It could help in the long term (millions to billions of years), though eventually we hit a point where we worry about what the Sun is doing and so forth.