@Kels_316 @johnquiggin @stilgherrian The thing the terraformers miss about Mars is that the only reason the atmosphere hangs around is gravity (which Mars has less of) and warming the atmosphere up makes its particles more energetic and more likely to reach escape velocity.

Mars is cold with a very thin atmosphere of heavy gasses because it's too small for an atmosphere of anything else. It doesn't matter how many years you spend terraforming, all your artificially produced air will escape straight into space, and you can't fix that without making the planet heavier.

Terraforming is SF, it isn't _real_. If we want an earth-like atmosphere, we need to start with an earth-like planet, similar mass, similar W/sq.m input from its star.

And we only have one of those.