Kurzgesagt – In a Nutshell
Sources - What Happens if we Nuke the Moon?
We would like to thank the following experts for their support:
Prof. Matthew Caplan,
Professor of Physics at Illinois State University.
Alex Wellerstein
Historian at the Stevens Institute of Technology.
– During the cold war the moon was a major target for space exploration and you know, military bases. So the US Air Force commissioned a serious study of the effects of a nuclear detonation on the surface of the moon.
Even though the study is around 60 years old, it is still one of the few publicly available studies on the effects of a nuclear detonation on the Moon.
#A STUDY OF LUNAR RESEARCH FLIGHTS, US Air Force Special Weapons Center, 1959
https://nsarchive2.gwu.edu/NSAEBB/NSAEBB479/docs/EBB-Moon02.pdf
Quote: “Nuclear detonations in the vicinity of the moon are considered in this report along with scientific information which might be obtained from such explosions. The military aspect is aided by investigation of space environment, detection of nuclear device testing, and capability of weapons in space.”
Back then the American space program was still entirely under military control. Next to scientific questions like “what happens if we nuke the Moon” they were also interested in setting up a Moon base to conduct surveillance operations and assist with scientific research.
#Project Horizon, US Army, 1959
https://history.army.mil/faq/horizon/Horizon_V1.pdf
https://history.army.mil/faq/horizon/Horizon_V2.pdf
Quote: “There is a requirement for a manned military outpost on the moon. The lunar outpost is required to develop and protect potential United States interests on the moon; to develop techniques in moon-based surveillance of the earth and space, in communications relay, and in operations on the surface of the moon; to serve as a base or exploration of the moon, for further exploration into space and for military operations on the moon if required; and to support scientific investigations on the moon. ”
Quote: “The scope of this study covers the design criteria and requirement of a lunar outpost, its construction and maintenance, and a summary of its operational aspects.”
– But just quoting stuff is boring, so let us conduct a very important scientific experiment with an imaginary 100 megaton thermonuclear warhead, about twice as powerful as the most powerful bomb ever detonated. We’ll also place a number of curious astronauts around the moon as observers.
The most powerful bomb that was ever detonated on Earth was the Tsar bomb with a yield of 50-megaton, equivalent to 2.1 * 1017 Joules or roughly the total power output of the entire world for a day.
#Tsar Bomba, Encyclopædia Britannica, retrieved 2020
https://www.britannica.com/topic/Tsar-Bomba
Quote: “Tsar Bomba [...] was detonated in a test over Novaya Zemlya island in the Arctic Ocean on October 30, 1961. The largest nuclear weapon ever set off, it produced the most powerful human-made explosion ever recorded.[...] It had a 100-megaton capacity, though the resulting fallout from such a blast was considered too dangerous for a test situation. Thus, it was modified to yield 50 megatons, which was estimated to be about 3,800 times the strength of the U.S. bomb dropped on Hiroshima during World War II. ”
The imaginary bomb we use in the video technically existed, it has the intended yield of the Tsar Bomba. However, it was considered too dangerous to detonate such a powerful bomb for testing so the yield of the Tsar Bomba was reduced by half.
– Let us push the button and slow down time. For the first few milliseconds nothing much happens outside our weapon. Meanwhile inside, high explosives send a shockwave to a radioactive metal core, compressing it so much that it reaches critical mass and starts a nuclear fission chain reaction, heating this first stage to a 100 million degree hot plasma, only to set off the second stage, which starts fusing atomic nuclei like the core of a star.
You can read a full description of all the steps a thermonuclear weapon takes to release its energy. In summary, a small atomic bomb (containing uranium) is detonated as a fission ‘trigger’ for a mass of fusion fuel. This second step releases a lot more energy. It also produces many neutrons that help extract even more energy by causing more fission. To reach the astounding 50 Megaton yield of the Tsar Bomba, a third stage is added. It contains an even larger load of fusion fuel that needs the energy from the previous stages to ignite.
#"Teller-Ulam" Summary, Nuclear Weapons Archive, retrieved 2020
https://nuclearweaponarchive.org/Library/Teller.html
Quote: “All thermonuclear weapons existing in the world today appear to be based on a scheme usually called the "Teller-Ulam" design (after its inventors Stanislaw Ulan and Edward Teller), or "staged radiation implosion" for a physically descriptive designation. Other designs have been devised that use thermonuclear reactions to enhance weapon yield in various ways, but the term "hydrogen bomb" can be taken to be virtually synonymous with this scheme.”
– Very briefly, our weapon contains one of the hottest places in the universe. And only now, barely ten milliseconds later, does the rest of the universe find out that anything has happened, as suddenly the bomb dissolves and a flaming star of nuclear death is born.
All the multiple steps and stages in a nuclear bomb are ignited and consumed within microseconds of each other. The bomb could have released almost all of its energy before its casing even ruptures.
#Introduction to Nuclear Weapon Physics and Design, Nuclear Weapons Archive, retrieved 2020
https://nuclearweaponarchive.org/Nwfaq/Nfaq2.html
Quote: “The convergent shock wave of an implosion can compress solid uranium or plutonium by a factor of 2 to 3. The compression occurs very rapidly, typically providing insertion times in the range to 1 to 4 microseconds.”
Quote: “The fusion reactions that occur in stars are not the same as the ones that occur in thermonuclear weapons or (laboratory fusion reactors). [...] The fusion reactions used in bombs and prospective powerplant designs are simple, and extremely fast - which is essential since the fuel must be fully consumed within microseconds. These reactions thus are based on the same general principles as stellar fusion, but are completely different in detail.”
– So far so good. But everything that happens now is very different from what we’re used to on earth because of one major difference: There’s no atmosphere.
The Moon does have some gases floating over its surface, but it forms a layer so thin and small that we can completely ignore it.
#Moon Fact Sheet, NASA, retrieved 2020 https://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html
Quote: “Surface pressure (night): 3 x 10^-15 bar”
– As the fireball shines it releases a flash of X-rays and thermal photons, a wave of silent heat which rushes outwards in all directions. On earth, this heat would char and burn everything within a 50 kilometer radius at least.
#The Effects of Nuclear Weapons, US Department of Defense and Department of Energy, 1977 https://www.dtra.mil/Portals/61/Documents/NTPR/4-Rad_Exp_Rpts/36_The_Effects_of_Nuclear_Weapons.pdf
Quote: “Because of the enormous amount of energy liberated per unit mass in a nuclear weapon, very high temperatures are attained. These are estimated to be several tens of million degrees, compared with a few thousand degrees in the case of a conventional explosion. As a consequence of these high temperatures, about 70 to 80 percent of the total energy (excluding the energy of the residual radiation) is released in the form of electromagnetic radiation of short wavelength. Initially, the (primary) thermal radiations are mainly in the soft X-ray region of the spectrum.”
We let our expert perform a couple of calculations in order to come up with the right radius of thermal radiation. There are many uncertainties with such an unprecedented detonation, but 50 km is in the right ballpark.
Quote: "Assuming 10% thermal emission, we obtain ~1e17 J / (4 pi (100 km)^2) ~ 20 cal/cm^2 which means there may be sufficient heat at 100 km for 3rd degree burns (typical threshold is near 10 cal/cm^2). However, the smaller radius of the moon affects this! The horizon distance on the moon for an astronaut (~2 m height) is ~sqrt(2hR)~2.6 km!
We can consider instead the horizon distance for the fireball- ie, since an astronaut observer is basically at ground level, then if the fireball has grown to height great enough that it can 'see' the astronaut then the astronaut can surely feel the heat of the explosion (ie there is a line of sight between them). So what's this height? 100-500 m is a good distance. At 500 m height, the horizon distance is approximately 40 km! In short, if you can see it, you're fried."
(from personal communication with Prof. Matt Caplan)
– 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.
#Gerard Kuiper, NASA, retrieved 2020
https://solarsystem.nasa.gov/people/720/gerard-kuiper-1905-1973
Quote: “He [Gerard Kuiper] predicted what the surface of the Moon would be like to walk on—"like crunchy snow". This was verified by astronaut Neil Armstrong in 1969.”
This “crunchy snow” on the surface of the moon comes from the melted material that cools into brittle fragments. It is as if the lunar surface was littered with tiny pieces of broken glass.
#The Lunar Sourcebook, David S. McKay et al., 1991
https://www.lpi.usra.edu/publications/books/lunar_sourcebook/pdf/Chapter07.pdf
Quote: “Studies of returned samples have shown that the bulk of this lunar regolith (informally called the lunar soil) consists of particles <1 cm in size although larger cobbles and boulders, some as much as several meters across, are commonly found at the surface.
Because the impact cratering events produce shock overpressures and heat, much of the pulverized material is melted and welded together to produce breccias (fragmental rocks) and impact melt rocks, which make up a significant portion of the regolith and add to its complexity.”
– 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 to glass. Any astronauts watching the show within about 50 km can expect to be fried.
#Trinitite redux: Mineralogy and petrology, G. Nelson Eby et al., 2015
http://www.helfordgeoscience.co.uk/wp-content/uploads/2017/01/Eby-et-al-2015.pdf
Quote: “The advantage of studying glasses from the Trinity site is that we have some knowledge of the conditions of formation; maximum temperature of ∼8400 K, relatively high pressures (at least 8 GPa), and a duration of 14 to 20 s with the maximum temperatures associated with the fireball existing for ∼3 s..”
In other words, the conditions inside a nuclear fireball can melt silicate rocks on the ground to give trinitite, which is green-coloured radioactive glass.
This is the charred ground surrounding a nuclear explosion, caused by heat radiating out of the fireball. It is where we first discovered the green glass we call Trinitite.
https://commons.wikimedia.org/wiki/File:Trinity_crater_(annotated)_2.jpg
– 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.
#A Review of Nuclear Explosion Phenomena Pertinent to Protective Construction, H. L. Brode et al., 1964
https://apps.dtic.mil/dtic/tr/fulltext/u2/601139.pdf
Quote: “ The radiation from the bomb materials at such high temperatures is mostly in the form of ultraviolet and X rays; and "light" from these high frequencies, unlike ordinary visible light, does not travel great distances in air. Rather, it is absorbed in the air immediately around the bomb, causing that air to be heated to temperatures in the neighborhood of 1,000,000C. [...]. The cold air is so opaque to soft X rays that a rather sharp, fast-moving front is maintained between the cold air outside and the hot air inside.
The initial radiative growth of this high-temperature sphere takes place before hydrodynamic shocks can develop. [...] an extremely strong spherical shock front develops and races onward at an extremely high speed. For a 1-MT surface burst, this transition should occur at a radius of about 170 ft from the bomb. The extremely strong shock, driven by the high pressures in this hot sphere, begins to compress the air some tenfold above normal air density and to force it outward close behind the shock front. Since the shock is expanding into continuously larger volumes of air, its strength, and consequently its ability to heat the air it engulfs, decreases rapidly with increasing shock radius.”
– 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.
#The Blast Wave, Atomic Archive, retrieved 2020
https://www.atomicarchive.com/science/effects/blast-wave.html
Quote: “The air immediately behind the shock front is accelerated to high velocities and creates a powerful wind. These winds in turn create dynamic pressure against the objects facing the blast. Shock waves cause a virtually instantaneous jump in pressure at the shock front. The combination of the pressure jump (called the overpressure) and the dynamic pressure causes blast damage. Both the overpressure and the dynamic pressure reach their maximum values upon the arrival of the shock wave. They then decay over a period ranging from a few tenths of a second to several seconds, depending on the blast's strength and the yield.”
As most data from nuclear testing comes from the United States, ‘psi’ or ‘pounds per square inch’ is used as the unit for pressure. Sea-level pressure is 14.7 psi.
#Explosions and Refuge Chambers, CDC, retrieved 2020
https://www.cdc.gov/niosh/docket/archive/pdfs/niosh-125/125-explosionsandrefugechambers.pdf
Quote: “The human body can survive relatively high blast overpressure without experiencing
barotrauma. A 5 psi blast overpressure will rupture eardrums in about 1% of subjects,
and a 45 psi overpressure will cause eardrum rupture in about 99% of all subjects. The
threshold for lung damage occurs at about 15 psi blast overpressure. A 35-45 psi
overpressure may cause 1% fatalities, and 55 to 65 psi overpressure may cause 99%
fatalities”
#Blast Injuries, Michael R. Jorolemon et al., 2020
https://www.ncbi.nlm.nih.gov/books/NBK430914/
Quote: “Primary blast injury is caused by the blast wave moving through the body. Since only high order explosives create a blast wave, primary blast injuries are unique to high order explosions. The blast wave causes damage to more extensively to air-filled organs. The resulting barotrauma can affect the lungs, auditory organs, the eye, brain, and gastrointestinal tract.
Blast ear – tympanic membrane rupture and middle ear damage
Blast lung – injury to the lung parenchyma, can have delayed symptom presentation
Blast brain – injury to brain parenchyma, even without direct injury to the head
Blast eye – rupture of the globe of the eye
Blast belly – injury causing abdominal hemorrhage and perforation (immediate and delayed). It can also cause injury to solid organs and testicular rupture.”
The shockwave from a nuclear detonation in an atmosphere is similar to the blast wave from a high explosive.
– 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.
Figure 8 shows how a nuclear explosion in space only produces a single pulse, through which it radiates almost all of its energy in the form of X-rays.
#Thermal radiation from Nuclear Explosions, Harold L. Brode, 1963
https://www.rand.org/content/dam/rand/pubs/papers/2008/P2745.pdf
#NUCLEAR WEAPON EFFECTS IN SPACE, NASA, 1959
https://history.nasa.gov/conghand/nuclear.htm
Quote: “[...] in the absence of the atmosphere, nuclear radiation will suffer no physical attenuation and the only degradation in intensity will arise from reduction with distance. As a result the range of significant dosages will be many times greater than is the case at sea level.”
– 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. But of course, this is not all.
#Biological Effects of Radiation, USNRC Technical Training Center, retrieved 2020
https://www.nrc.gov/reading-rm/basic-ref/students/for-educators/09.pdf
Quote: “If radiation interacts with the atoms of the DNA molecule, or some other cellular component critical to the survival of the cell, it is referred to as a direct effect. Such an interaction may affect the ability of the cell to reproduce and, thus, survive. If enough atoms are affected such that the chromosomes do not replicate properly, or if there is significant alteration in the information carried by the DNA molecule, then the cell may be destroyed by “direct” interference with its life-sustaining system”
A nuclear detonation creates a high dose of X-ray and neutron radiation. The dose is measured in ‘rad’ and is responsible for the effects listed above.
– While all of this happens the explosion hammers against the moon, transferring about a tenth of the explosion energy into seismic waves, powering an intense moonquake. The moon is much smaller than the earth, and our astronauts will feel an inescapable violent shaking no matter where they’re standing.
#A STUDY OF LUNAR RESEARCH FLIGHTS, US Air Force Special Weapons Center, 1959
https://nsarchive2.gwu.edu/NSAEBB/NSAEBB479/docs/EBB-Moon02.pdf
Quote: “In a high energy nuclear explosion above the surface of the moon, it has been estimated that the effective agency of energy transfer to the surface of the moon will be x-rays produced by the explosion. The energy of the bomb converted into this form is in the order of one-half its total energy of which less than one-half again will be directed toward the surface of the moon. The exact mechanism by which seismic energy is generated by an atomic explosion is not known. But of the total energy reaching the surface a considerable fraction must be expended in heating and vaporization of the surface layers of rock. A crude estimate would be that energy transfer into seismic energy is 0.1 as large for an above surface detonation as for the detonation of the same bomb when buried underground.”
– Comparable to a 7 Richter scale on earth, this shaking could seriously damage or even level infrastructure we might have built anywhere on the moon. Those who hid on the far side of the moon would have no idea it was an explosion, the quaking would feel like an asteroid the size of the Great Pyramid had struck.
#A STUDY OF LUNAR RESEARCH FLIGHTS, US Air Force Special Weapons Center, 1959
https://nsarchive2.gwu.edu/NSAEBB/NSAEBB479/docs/EBB-Moon02.pdf
Quote: “Under these assumptions a kiloton bomb exploded just above the surface of the moon would be the equivalent (insofar as seismic detonation on the moon) of an earthquake upon the earth of magnitude M=4.5 on the Richter Scale. Similarly, a 1 Megaton bomb so detonated would be the equivalent of an earthquake of magnitude M=6.2 on the Richter Scale.”
Following these equations, a 100 Megaton bomb would create a ‘moonquake’ on magnitude M=7.
– And this is still not the end: Where our bomb exploded, the ground is splattering like water when a rock strikes a pond. 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.
In order to determine how much soil or rock is excavated, cratering tests were done with high explosives in the single-ton yield energy range and with nuclear detonations in the kiloton to Megaton yield range. We find that for 1 ton of energy 400 ft3 (11.3 m3) is appropriate for the lunar surface. This means that a 100 Megaton yield detonation would excavate about 40,000,000,000 ft3 (which is 1,132,673,860 m3 or 1.13 km3).
#Estimates of crater dimensions for near-surface explosions of nuclear and high-explosive sources, Cooper, Jr. H F, 1976
– 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 will have a really bad time though.
The lunar escape velocity is only 2,380 m/s. Plenty of debris from a nuclear detonation will reach and exceed this velocity, allowing it to escape the Moon’s gravity.
#Moon Fact Sheet, NASA, retrieved 2020
https://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html
Quote: “Escape velocity (km/s) 2.38”
– What about the moon’s orbit? It is basically unchanged. Trying to move the moon with a nuke is like trying to move a truck by blowing on it. Nuclear explosions may be big, but space is bigger. Our mighty explosion only left another crater. One among millions.
To give you a better understanding of how far away we are from moving the Moon, let these numbers sink in. The Moon masses 73.4 billion billion tons. Even if the energy of our 100 Megaton yield bomb was completely converted into kinetic energy, it would only accelerate the Moon by a negligible 3.37 mm/s. That’s a fraction of a thousandth of a percent of the Moon’s orbital velocity of 1022 m/s. In reality, only a fraction of the blast’s energy actually pushes the Moon, so its effect on the lunar orbit is completely inconsequential.
#Moon Fact Sheet, NASA, retrieved 2020
https://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html
Quote: “Mass (10^24 kg) 0.07346”
– 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.
#Radioactive Fallout, Atomic Archive, retrieved 2020
https://www.atomicarchive.com/science/effects/radioactive-fallout.html
Quote: “Most of the particles decay rapidly. Even so, beyond the blast radius of the exploding weapons there would be areas (hot spots) the survivors could not enter because of radioactive contamination from long-lived radioactive isotopes like strontium 90 or cesium 137. For the survivors of a nuclear war, this lingering radiation hazard could represent a grave threat for as long as 1 to 5 years after the attack.”
The Moon does not have any natural mechanism like rain or wind to clear radioactive fallout from its surface. It will be concentrated into a thin layer right at the top, unlike on Earth where it can be diluted and washed deeper into the ground.