I thought it might be interesting to compare an atomic blast on the Moon vs. Earth. Just in case we need to make a new crater or something. I can think of several differences.
Initial crater. I know the Moon is covered with loose material but how deep is it before bedrock is exposed? Would the initial crater on the Moon be larger then the one on Earth?
Blast zone. A shock wave would not exist or at least would be limited to any temporary “atmosphere” that the explosion created. However, there would be a large radius where small particles would “shotgun” everything they hit. Those particles would be traveling at a velocity similar to a shock front?
Heat blast. Would the radius of damage from intense heat be larger since there is no air to absorb any radiant heat energy?
Immediate fallout zone. Most of the debris from an atomic bomb falls to ground fairly quickly in a matter of hours. Obviously the radius of fallout would be far larger due to the lack of atmospheric drag. But the radiation level within that zone would be much lower than the Earthly zone.
Extended fallout zone. On the Moon there wouldn’t be any extended zone since there is no air to support any dust and no winds to disperse it.
The mushroom cloud. On Earth the fireball rises until the atmospheric drag slows it down and it billows into the familiar mushroom cloud. Would there be one on the Moon or would the ejecta just form a jet heading into space? Would it reach orbital or escape velocity?
Decay rate of the fallout. Since the fallout is exposed to far higher solar radiation than on Earth would the rate of decay (half life) be affected at all or is that strictly a function of the material properties of the radioactive particles?
The primary initial yield of a fission reaction is in the kinetic energy of the fission fragments, the fast neutrons, and some small portion of gamma rays (high energy X-rays) that comprise about 7% of total energetic yield for a pure fission reaction. Various design methods are used to enhance X-ray yield to increase the effective explosive yield of the weapon (as measured in terms of TNT equivalent); however, this depends upon having an atmosphere to absorb the X-rays and produce the thermal effects that create shock and blast.
On the surface of the Moon in almost complete vacuum, there would be almost no blast effects other than the energy absorbed by the bomb components (tamper, casing, other structure and physical hardware) and nearby regolith. Aside from the very bright flash that would mostly be above the UV spectrum and the prompt emission of fast neutrons, there wouldn’t be the kind of effects that we see on Earth. There would be a relatively small blast zone compared to what would be observed on Earth, very little ‘heat’ (randomized kinetic energy), and essentially no fallout and no mushroom cloud which is a fluid dynamic effect of the atmosphere absorbing so much X-rays and converting them to thermal energy that it creates a massive uprush that sucks up material from the ground and mixes it with the radioactive residues of the device producing the fallout. The decay rate of radioactive processes is utterly unaffected by solar radiation, although there might be very minor effect local to the proximity of the detonation for neutrons emitted by radioactive residue to stimulate fission at a slightly amplified rate.
It seems to me that anything (or a lot of things) that would be reduced due to the lack of air friction would similarly be increased due to the smaller gravitational pull.
For example, dust that might fall faster because of the lack of air friction would also fall slower because there’s less gravity pulling it back down. Whether that would result in more or less ‘air’ time, I don’t know. And, at the same time, that same lack of air friction would mean particles could get much further from the blast zone with nothing to dampen the horizontal component of their trajectory.
As for the crater, my gut says it would be deeper since the explosion wouldn’t have to push the material nearly as hard to get it up and out of the hole, leaving more energy to do more damage.
In Isaac Asimov’s short-short “Silly Asses” Earth is entered in the book of civilizations that had matured enough to be extended membership in the Galactic Federation because it had developed thermonuclear power, then immediately stricken when the record-keeper learns it was before space travel and thus, the first bomb was detonated on its own planet.
Kurzgesagt – In a Nutshell checked the likely effects a few years ago:
On earth, this heat would char and burn everything within a 50 kilometer radius at least. But on the moon, without an atmosphere and oxygen-rich air, there’s no burning at all. Also there are no things to burn. The crunchy topsoil of the moon is made from silicate rock and metals chewed to dust by eons of meteorite impacts, mixed with tiny traces of water. When heated by the explosion, X-rays from the fireball vaporize a thin cloud of rock from the lunar surface, while the unlucky dust that’s inside the fireball melts into glass. Any astronauts watching the show within about 50 km can expect to be fried.
And now, we begin to see one of the biggest differences between explosions in space and on earth. On earth the atmosphere fights back against the plasma bubble: Its expansion is violently stopped within moments by the pressure of the atmosphere. But this is not good news. As the fireball rams the atmosphere it produces the most destructive part of a nuclear explosion on earth: the shockwave. Compressed air around the explosion rushes out faster than the speed of sound, shattering buildings and roaring so loud it ruptures organs. But on the moon there is no shockwave. No atmosphere means nothing to impede the expanding explosion in space. On the moon, the fireball just grows in eerie silence as there is no atmosphere to stop it or to give it a voice. This would be an amazing thing to watch from a safe distance. Unfortunately there’s hardly any safe viewing distance for a nuclear explosion on the moon. Without an atmosphere weakening the deadly ionizing radiation that can scramble DNA, anyone close enough to get a good look will be exposed to fatal amounts of radiation.
As the explosion pushes against the surface it may excavate as much as a hundred million cubic meters of dust and rock, forming a crater a kilometer across while bedrock is pulverized to rubble. Debris is shot into the sky in every direction. Again without an atmosphere there’s no drag to slow any of it down. Much of the debris scattered never returns to the moon, flying off faster than escape velocity. A flurry of micrometeorites have been cast off to explore the solar system, many of which will rain down on the earth, though few will be larger than pebbles. Any satellite, astronaut or space station in the way though will have a really bad time.
Finally, our explosion comes to an end. On earth, the fireball rises like a hot air balloon forming a sort of stalk; as it reaches up cooler air is drawn in around it, rounding the top into a mushroom cloud. But on the moon, well, you know by now: no atmosphere, no mushroom.
Still, anyone on the moon will continue to not enjoy themselves. The material that ends
up raining back to the moon is radioactive, and without any natural processes to wash it away or bury it, the surface of the moon will remain contaminated. Although fortunately, the worst of the radiation will have decayed to a level comparable to natural levels from cosmic rays in about a year.
In conclusion, we can say with confidence that while the moon itself does not care about being nuked and will barely notice, using the moon as a nuclear test ground kind of ruins it for everyone trying to spend some time there or to build something useful. So maybe we should just not do that.
Yeah…my first thought is that, aside from the radioactive particles, a nuke going off on the surface of the moon would be almost indistinguishable from other low altitude energetic events, i.e., meteors forming craters.
On the Moon, wouldn’t it make sense to explode the bomb at ground level rather than an "air"burst like we do on Earth? If so, would that significantly change the effect?
We do groud burst on Earth as well. Or, did in testing, anyway.
I imagine that a greater portion of the radiated energy vaporizes and ionizes lunar regolith and all the rest still radiates away into vacuum as @GIGObuster’s cite talks about.
Not much really changes, because of the lack of atmosphere.
Waddya mean? I haven’t seen any ambassadors from the Galactic Federation arriving to welcome Earth to the Federation, have you? Isaac seems to have gotten it right.
