Nuclear Explosion on the Moon?

Factual Questions
1

I’m sorry if this has already been a thread – I must admit I didn’t search, and this seems to be one of those dumb “what if” scenarios that will never happen but nevertheless make me curious.

Back in the Manhattan Project, that (excuse my French) arrogant b##stard Edward Teller, a man I heartily despise – almost brought everything to a screeching halt by suddenly positing that “The Gadget” could potentially ignite Earth’s atmosphere.

Coming from a respected physicist as he was, it gave serious pause to a lot of the other physicists, and I believe all work was actually halted while they held a conference about this.

Of course, we know that’s completely impossible now, but these guys had never even SEEN a nuclear explosion, and quite frankly, most of them had no idea beyond theory of exactly what they were dealing with (consider the disastrous test named Castle Bravo, in which the scientists underestimated the yield by a huge margin and actually caused the death of a Japanese sailor in a fishing vessel that was not detected and damn near killed some technicians who were on the other side of the Bikini atoll).

Anyway, Tsar Bomba, which was actually designed by Andrei Sakharov, among others, and yielded an incredible 58 megatons, or, according to Wikipedia, “about 1,350–1,570 times the combined power of the bombs that destroyed Hiroshima and Nagasaki,” was the biggest nuclear test ever conducted by anyone (and apparently the scientists were so nervous about the whole thing that they actually SCALED BACK the projected yield of 100 megatons – one million tons of TNT).

My question here is entirely hypothetical but seems at least to me to be interesting.

What if somehow, someone conducted a surface thermonuclear test on the moon, say, at the maximum yield one can imagine (I don’t believe there are any limits, as it depends on how much secondary fuel you add to the initiating fission explosion).

So let’s just assume that they decided to make this explosion 1,000 megatons – I do believe that would be ten million tons of TNT – and exploded it, say, ten miles above the surface of the moon.

First of all, can nuclear explosions work in vacuums? Second of all, compared to, say, the Tunguska Event, or even the Chixulub event, what kind of damage would this do?

Sorry to be so vague, but after just reading about the US Navy’s testing of an “energy cannon” I just can’t help thinking that this is something our Boys With Toys would just love to do.

2

Wouldn’t 100 megatons be 100 million tons, not one million tons?

3

Yes, nukes can work in a vacuum. 1,000 megatons would leave one hell of a crater on the moon, though Chixulub is thought to have delivered 100 teratons of TNT.

4

It would create a 70s era TV show.

5

And lots and lots of disco.

6

As above, nukes detonate just fine in a vacuum. BUT, they’re “just” insanely bright flashes of mostly X-rays. If detonated on the surface the energy imparted to the adjacent rock is huge, much like surface tests on Earth. So you’d get a correspondingly huge crater from a 1000MT = 1GT blast.

But the OP specified a burst at 10 miles above the surface. That’s going to have a very different result.

With an air burst on Earth the X-rays couple to the atmosphere, creating the thermal & blast wave that does most of the destruction. In the vacuum above the Moon that would not happen. A pretty intense X-ray flux would still hit a large area of the Moon. But the effect might be more like creating a 1 mile wide shallow pond of instant molten lava surrounded by a 30 mile diameter region of warm rock. All of which then rapidly cools back down to ambient temperature.

IOW, the effects might be pretty anticlimactic.

7

There would be a bright flash and some ejecta, forming a new crater. But since there’s no atmosphere, you wouldn’t get a thunderball or mushroom cloud, or anything like that. A really big blast would, I assume, turn a large chunk of the Moon’s surface into glass from the heat generated. The shock wave would probably reverberate inside the Moon for weeks, but the only things you’d have to worry about above the surface would be the radiation and the ejecta.

8

It nearly happened in reality

a project to explode a nuclear bomb on the Moon; Carl Sagan worked on the project.
Only a kiloton or so, this would have been a tiny, brief flash and might not even have been visible from Earth, although the dust cloud might have been visible at the terminator…

9

Space: 1999

10

In both cases, you appear to be off by a factor of 100:
100 megatons = 100 million tons, not one million
1000 megatons = 1000 million tons (one gigaton), not ten million

11

I think you have pretty high standards of what constitutes ‘climactic’

But recognizing the otherwise sound technical analysis… a lot of the surface would necessarily vaporize, would it not? What would happen to that big cloud of vaporized regolith? I assume there would be a big semi-spherical expansion, but it wouldn’t rise like it would on earth would it?

12

There’s no atmosphere, but gas would be generated from the vaporized soil and rock. It would dissipate pretty quickly in the vacuum of space, and the ejecta would be hurled quite a way away becuase of the Moon’s low gravity. I suspect that some of the debris might even be hurled into open space and into its own orbit.

A lot would depend on how deeply the device was embedded in the Moon’s surface. Detonated above the surface (an “air burst,” so to speak), it would just shower the surface with radiation across the spectrum.

13

For what it’s worth, the bit about igniting the atmosphere was a joke, and the “all work stopped” was the guys who happened to be present at the time he said it spending about five minutes calculating and verifying that it couldn’t happen. This is the kind of thing that physicists do for fun, and over their lunch break.

14

Actually, the Soviets scaled it back from 100MT to ‘only’ 50 not merely because they were afraid of the larger explosion. In order to get double the yield the bomb had to use a Uranium case (or tamper). Thing is this not only doubled the yield it would have increased the ‘dirtiness’ of the explosion by several orders of magnitude. I’ve read that had they used Uranium this one test bomb would have increased the then total worldwide amount of nuclear contamination by several factors. So they used a Lead tamper instead.

In terms of a global perspective, minus the extra fallout, there would have been little long term, world-wide difference in the impact of a 100MT test over a 50MT one. In fact, these huge tests began to show that bombs of this scale had a serious diminishing return problem. The fireball was so immense that most of it detonated above & outside the atmosphere, causing little military destruction. Plus, when delivered by a manned bomber (as the Tsar Bomba test was) there was a serious risk to the bomber crew not surviving the detonation (I’ve read the Soviet crew thought they had about a 50/50 chance of living!)

This mattered because it was (correctly) believed that you could theoretically keep adding stages to an H-Bomb indefinitely, making a bigger & bigger explosion.