Space/Science — HabitableZone

Space/Science » in reply to Terrafroming Venus

Nope
Adam — (archived)

Hi Scott

Venus is pretty hot, but to lose atmosphere basically you have to put in as much energy as it'd take to lift every 1000 tons/sq.metre of atmosphere from all of Venus' 460 trillion square metres. Escaping Venus takes about 54 megajoules per kilogram. Thus 4.6 x 10^20 kg x 54 x 10^6 joules = 2.484 x 10^28 joules. Venus gets 2,615 Joules of Sun per square metre per second, some 3 x 10^17 Watts over its total area. Thus it'll take about 10^11 seconds to heat it up via perfect application of sunlight. That's over 2,600 years and even longer for lower efficiency.

You might think: well why not make it hot to puff the atmosphere up so it'll escape into space? But where has the energy come from for an atmosphere to escape and be puffed up to start with? A hot atmosphere is one packed with energy and as it expands it does work, and also does work against Venus' gravity. All energy and you'll find it'll be at least equivalent to launching it all into space at escape velocity - if not more!

A big enough impactor to supply 2.5 x 10^28 joules... well it'd be BIG. Or maybe lots and lots of high velocity impactors? A 50 km/s impactor packs 125 megajoules/kg so you can see it'd only blast roughly 2 kg of atmosphere away for every kilo of its own mass - call it 2 x 10^20 kg. At a density of 920 kg/m^3 (ice) it'll be 3,400 km across.

Ouch!

Adam

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