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I was reading about the Farnsworth fusor last night. The thought occurred to me that a similar device on a huge scale could potentially be used to confine an atmosphere on a small body like Ceres or Vesta. This would work by confining positive ions inside a spherical, positively charged net encasing the world. All upper atmospheres are essentially composed of a mix of positive ions and neutral atoms. So a global electric field could presumably be used to trap the ionosphere and even provide a net pressure on the upper atmosphere that replaces the effect of gravity.
The concept would work something like this:
(1) Construct a carbon fibre mesh across the surface, such that it forms a global spherical net with extended diameter ~100km greater than the encircled body;
(2) Raise the net on a series of steel or masonry towers, to its required height;
(3) Connect the net to a DC power supply, such that the net has positive electric charge of ~1KV w.r.t the surface;
(4) Begin melting surface ices such that the space under the net begins to fill with diffuse gas. At first, the mean free path of the gas molecules will be long enough to allow direct escape. As they approach the net, the positive charge will strip electrons from the molecules and would repel the positively charged ions, thereby trapping them in;
(5) As the concentration of gases gradually increases, the atmosphere will differentiate into two layers:
a. A cold, dense lower atmosphere of neutral gas, with short free paths and low molecular velocities;
b. A more diffuse upper atmosphere, containing high temperature ions.
(6) The ions would thermalize due to collisions amongst themselves and would lose heat both by radiation and by collision with colder molecules lower in the atmosphere. Eventually, as the atmosphere grows progressively thicker, only a tiny minority of upper atmosphere ions would have sufficient energy to escape the electric field;
(7) The electric field must have sufficient strength to effectively reverse the course of any ion escaping from the top of the atmosphere. This suggests to me that the force acting on an individual ion should be at least equivalent to the gravitational force that it would experience Earth’s gravity. However, this corresponds to an electric field gradient of only 3x10-6V/m, which seems extremely low.
(8) We are essentially using an electric field to contain the pressure of the atmosphere. Hence the pressure exerted by the electric field on the upper atmosphere at the scale height, must be at least 37% of the ground level gas pressure. Assuming ground level pressure is ~25KPa, that equates to a field induced pressure of 9.2KPa.
If it could be made to work, it would appear to allow the terraforming of almost any moon, comet or asteroid, even relatively tiny ones like Phobos and Deimos may be possible. As the atmosphere is compressed by the electric field, it would also reduce the amount of gas needed to terraform. As voltage increases, the force acting on individual ions within the field increases and the force exerted on the atmosphere as a whole increases, thereby reducing the scale height.
My own electrical engineering knowledge is limited. Can anyone here spot any fundamental physics problems with this idea?
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That sounds interesting. Could a trap for ions be made which might trap icons from the tail of Venus?
Done.
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Having looked into this in a bit more detail, it doesn't look so promising. Two reasons:
1. In order to maintain an 8KPa pressure at the top of the atmosphere and a voltage drop of 3MW/m (i.e. breakdown voltage for air) the energy consumption of the field is 8kW/m2. That would make electrostatic confinement somewhat energy hungry.
2. From Newton's third law, the force imposed upon the ionosphere is balanced by an equal and opposite force on the electrostatic grid. Hence, the grid still has to have the same strength as a world house supporting members. The electric field is therefore redundant. One might as well use glass or plastic panes in a metal lattice to contain the atmosphere.
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