Hi All

Phil wrote...

I had a figure of 40 million tons/year, but I must have lost an 0 somewhere. Still a neat hope, overall. Some super greenhouse gas is needed. I think I remember reading that CO2 was 1000 times more effective than methane, or maybe I got that backwards. SPF 50 is sure a great sun blocker! Somehow I think Venus is a better bet. Easier to subtract gas than add it.

...Mars only needs a tiny amount of flurocarbons about ~ 0.2 Pa to raise the temperature to cause release of any adsorbed CO2. Since Mars has ~ 144 trillion square metres that works out as ~ 8 billion tons, or 156 million tons per year over 50 years. Sounds huge, but wait...

Venus has 460 trillion square metres of area with a 96.5% CO2 atmosphere at 92 bars - that's 1000 tons per square metre, or 460 quadrillion tons of excess CO2. To remove it physically requires 108 megajoules per kilogram - or 108 terajoules per square metre. In total that's ~ 5 x 10^28 joules, and at ~ 5 tons per second would take ~ 36 times the Earth's current power output and 3 billion years to finish the job.

As you can see easier said than done. Hence why current atmospheric removal options are (1) chemical fixation (= making it into carbonates ) , (2) physical fixation ( = making it into CO2 polymer, or "carba" ), and (3) cooling the atmosphere with a soletta until it freezes/liquifies out, then covering it in insulation/ocean. All three have pluses and minuses and would require large space-going resources - (1) needs minerals for fixation and a cooling soletta so the carbonates don't decompose (2) needs a way of making stable carba and a cooling soletta, and (3) needs a full coverage soletta and an imported ocean. All very tricky and expensive.

Much cheaper in terms of colonisation is to build floating colonies in its atmosphere - N2/O2 breathing mixtures are lifting gases in all that CO2, plus the near-Earth pressure/temperature layer rotates once every 4 days or less, rather than the 116 day Sol on the surface. If the inhabitants want a milder surface climate then a small soletta can cool the clouds until they rain out - without the sulphur compounds in the atmosphere the temperature would drop to ~ 350 degrees C, dropping perhaps enough in the highlands for surface operations. But high temperature materials for machines and circuits are available so ROVs could mine and explore the surface even today.

The task on Mars is much, much easier - it has water, carbon dioxide (albeit adsorbed) and a currently livable surface, plus two handy moons chock full of volatiles.

Adam