first you build a time machine, then go into the distant future to retrieve wormhole technology, then just open up one end on a planet with a donor atmosphere.


all the other methods are even more impractical.

I don't think Mars could hold on to an atmosphere anymore. Its magnetic field is for shit.

Ask Kim Stanley Robinson.

http://en.wikipedia.org/wiki/Mars_trilogy

It depends on the atmosphere you're going for! With Mars, I'd suggest some soft red mood lighting, scented candles, and late 70s space rock.

Putting a gigantic electromagnet in orbit should do it.