I said setting a nuke off on the moon would pretty much contaminate the whole thing, and that relatively speaking this wouldn't much matter in terms of danger to astronuats. The effective fall out range of something in lower gravity and with no atmosphere is different. There is no atmosphere to slow particles from drag and the escape velocity is 2400 m/s, shoot a bullet at 800 m/s at a 45 degree angle on Earth and it will land within a couple miles, from the higer gravity yes but especially from drag effects.

Shoot it on the moon and it's going to travel several hundred miles, a much longer relative distance on the moon whose area is about 7% of Earth's. Means a bomb blast with 800 m/s shrapnel on Earth - low for most explosives - would litter a mile or so maybe but on the moon would leave shrapnel spread out over a few percent of it's surface. Needless to say bit of un-fissioned uranium blown out by an A-bomb often have speeds of 2400 m/s, some more, and they'd blow out into the void, some just less, and they'd fall on the other side of the moon. Set off an explosive with an expansion rate equal to or greater than the escape velocity of an object that has no significant atmosphere, and bits of the debris will be everywhere, if not evenly thickly.




If you hit the planet with something moving faster, relatively, then the escape velocity of the planet, you'd lose some in the initial strike, that's complex and there's modeling on that I'm not too familiar with. Otherwise it will all stay there, and you lose small fractions with time. The 1/6th rule I recall vaguely from memory is, I believe, based on observations of planet's by their mass and atmosphere density determining that those worlds under a certain threshold wouldn't retain atmosphere over billions of years, not millions let alone thousand. Oxygen is the third most abundant material in the Universe and 8 and 16 times more massive in it's common form than the 2nd and first most abundant respectively. If it leaked 1% a millenium and was a void in 100,000 years it wouldn't 'retain' in the astronomical sense but in all probability such a loss would be considered trivial to anyone who added stuck it there manually in the first place, but it would vent hydrogen faster and you'd need to add that, to keep the water, and frankly it's a cheap commodity. In any event, last I'd heard the earth vented about a kilogram into the void every second, mostly hydrogen with helium as about 5% of that and oxygen much less, our atmosphere masses, as it turns out, 14 pounds per square inch or about 10^17 pounds. So an annual loss of about 30,000 tons compared to about 50,000,000,000,000 tons, means even if that leakage was all oxygen and nitrogen, as opposed to virtually none of it, we'd be talking some billion years. If Mars was leaking a thousand times faster we'd be talking some million years. I'm not sure if anyone's actually done a rigorous calculation on the matter but replacing a few thousand tons, or even a few megatons, of air a year is a pretty trivial problem compared to sticking it there in the first place, especially since Mars already has uncounted megatons of oxygen in the native minerals. Sand is over half oxygen by mass and that red crap we call rust that colors that planet is mostly oxygen, I hate to point out the obvious but the byproduct of turning rust into iron is iron plus carbon dioxide, which in turn gets sucked up by plants into plant mass and oxygen... the world currently produces several hundred megatons of steel each year and a like amount of CO2, and thus oxygen, so even that super pessimistic megatons leakage figure would be pretty irrelevant in that it could be fixed by scooping up that rusty iron and making it into steel for the building and such.

Mars terraforming isn't exactly an underdeveloped discussion, we keep it in vague terms because there's a lot question marks about best method and specifics.




Yeah, if you wrap an H-bomb core with more U or P you get a dirty weapon, that's sort of a deliberate act though, Joel, and incidentally generally has to do with Uranium happening to be a handy thing to make the exterior cone of a missile re-entry vehicle out of anyway. Using 100 kilos of plutonium in a raw A-bomb and using it as catalyst for an H-bomb still produces parallel amounts of that 100 kilos as byproduct, you just have way more energy released, I'm not sure what the left out byproduct is, percentage-wise, but I'd guess an H-bomb leaves less un-fissioned in absolute terms and of course considerably less as a percentage of energy produced.

In any event the plan would either be to nuke it from orbit and have the blast expend a maximum amount of energy over an optimized amount of land, baking the oxygen out of it, or burying the nukes an optimized distance under the ground so the heat diffused into those upper layers and baked the oxygen out but near enough that most of the oxygen could escape the ground into the air, I really have no idea what that depth would be or which method would be better, but I'd be ton the sub-surface detonation leaving less contaminants around to endanger people compared to an aerial or surface blast.




Like I said, I don't trust the article or commentary on the subject to be very accurate, but nuking the moon or Mars doesn't even set my threat radar off concerning humans, I'd be worried about damaging the geology of the moon when we hadn't studied it yet, back then, myself, more than the possible accident option of the nuclear material blowing up during launch or boost phases. A rocket exploding on the pad and spraying the vlast radius with nuclear contaminants isn't much worse then it blowing up on the pad anyway, and frankly I wouldn't expect a big ball of uranium or plutonium to seriously fragment if the rocket blew up, a single, or even a few dozen, dense shards of fissionable material tumbling onto land or sea isn't exactly nothing but then neither is a train derailing at speed in the middle of city. If it totally atomized into fine dust on the way down it would be spread over some ellipse hundreds or thousands of miles long, radiation isn't to be laughed at but the better part of a million square miles would be a hell of a diluting factor, Nagasaki and Hiroshima were moderately dirty weapons and they hardly made the entire Archipelago there dangerous. Fragments would be easier to cleanup but totally fragmentation probably wouldn't even need it.

In any event, we shoot plutonium up into space regularly already, we used about a bomb's worth of the stuff in that new Mars rover.