Thinking about it, I reckon that focusing on gravity is probably the wrong way to go. (not that this necessarily stops anything - these *are* fen we're talking about here) The two main things Mars needs for long term viability are an atmosphere and a magnetosphere. Atmosphere's the easiest part of this - it's never going to be a full 1 bar, but a good .75 to .85 bar at "sea level" is possible - so the tricky bit is setting up a magnetosphere to protect the new air.
The best way to do this IMO is to restart the core. Adding energy to the cooling iron core would spin it up a little & give us a nice new magnetosphere. It'd also have the side benefit of restarting tectonic activity, maybe even reactivate the Tharsis Montes. That would be useful for very long term viability. So how do we do it? Well, that's a problem for another day; the atmosphere should be stable for the short term (for values of "short term" running into the 2200s at least) and that's more than enough time to come up with something.
Mr. Fnord interdimensional man of mystery
FenWiki - Your One-Stop Shop for Fenspace Information
"I. Drink. Your. NERDRAGE!"
The best way to do this IMO is to restart the core. Adding energy to the cooling iron core would spin it up a little & give us a nice new magnetosphere. It'd also have the side benefit of restarting tectonic activity, maybe even reactivate the Tharsis Montes. That would be useful for very long term viability. So how do we do it? Well, that's a problem for another day; the atmosphere should be stable for the short term (for values of "short term" running into the 2200s at least) and that's more than enough time to come up with something.
Mr. Fnord interdimensional man of mystery
FenWiki - Your One-Stop Shop for Fenspace Information
"I. Drink. Your. NERDRAGE!"