Fiction Science: NOVA, the Destroyer of Worlds

We knew the world would not be the same. A few people laughed, a few people cried, most people were silent.

I remembered the line from the Hindu scripture, the Bhagavad-Gita. Vishnu is trying to persuade the Prince that he should do his duty and to impress him takes on his multi-armed form and says, “Now, I am become Death, the destroyer of worlds.”

I suppose we all thought that one way or another.
— Dr. J. Robert Oppenheimer, The Decision to Drop the Bomb, 1965

Those words still weigh heavy on us today, over seventy years since the Trinity test, the first ever detonation of an atomic weapon on July 16th, 1945, and over fifty since the release of the film in which it was spoken, The Decision to Drop the Bomb in 1965. While the threat of nuclear war has mostly faded from public consciousness, the destructive power of nuclear weapons today is many orders of magnitude higher than it was in 1945. The same goes for the nuclear weapons of the 26th century. Just as it would be hard to fathom that Russia built a weapon 2,000 times more powerful than the one in the video above a mere twenty years later, it is hard to imagine how much energy mankind could wield for war given another five centuries.

Halo may be a work of fiction, but keep Oppenheimer’s words in mind when reading this. We will be discussing a weapon that is more powerful than anything this planet has ever seen. Literally. More powerful than the Tunguska event over Siberia in 1908. More powerful than the impactor that is blamed for wiping out the dinosaurs 66 million years ago. Even more powerful than the theorized collision between the Earth and a Mars-sized object 4.5 billion years ago that formed the Moon. Today we will be discussing the most powerful weapon in the UNSC’s arsenal, the NOVA Bomb.


The following article makes reference to and could potentially contain spoilers for Halo: Ghosts of Onyx and Halo: Envoy.




To answer this question, we will have to break it up into a few parts, as usual, and combine them at the end to get our answer. Firstly, we have to figure out how much energy is released in a NOVA Bomb, then we can use that to figure out how big the bomb would have to be in order to output that much energy. I am going to do my best to not get ahead of my writing, so we will figuring these out together, so-to-speak. To start, lets review the two instances a NOVA bomb was detonated in-lore, and use that information to make a best estimate as to the energy output of the bomb.


For anyone unaware, a NOVA bomb is, as far as we know, the most powerful weapon in the UNSC arsenal. It has never appeared in a game, but two have been used in the Halo universe. The first was on November 3rd, 2552, following the Fall of Reach and at the same time as the Battle for Earth and Battle of Installation 05. The bomb was left on the surface of Reach by Vice Admiral Danforth Whitcomb with the intention of the Covenant discovering and collecting the bomb for study. The ploy worked, and after some unplanned help from a group of Huragok on the carrier Sublime Transcendence, the NOVA Bomb detonated inside the ship and within a Covenant fleet, destroying over three-hundred ships, scorching the facing side of the planet Joyous Exultation, and SHATTERING the planet’s moon, Malhiem. Ghosts of Onyx describes the scene:

The voice from the box started again—now loud and clear:

“This is the prototype Nova Bomb, nine fusion warheads encased in lithium triteride armor. When detonated it compresses its fusionable material to neutron-star density, boosting the thermonuclear yield a hundredfold. I am Vice Admiral Danforth Whitcomb, temporarily in command of the UNSC military base Reach. To the Covenant uglies that might be listening, you have a few seconds to pray to your dammed heathen gods. You all have a nice day in hell.”

Kwassass pushed his way through the throng of Huragok. He had to get to the thing. Pull those wires.

There was a flash of the most beautiful light, and more glorious heat than he’d ever—

A battle group of eighteen destroyers, two cruisers, and one carrier collected in high orbit over Joyous Exultation, and drew in a spherical formation about their flagship, the Incorruptible. They shimmered blue-white and vanished into Slipspace.

A heartbeat later Vice Admiral Whitcomb’s ploy of slipping the UNSC prototype Nova Bomb into Covenant supplies had finally paid off: a star ignited between Joyous Exultation and its moon.

Every ship not protected on the dark side of the planet boiled and vaporized in an instant.
The atmosphere of the planet wavered as helical spirals of luminescent particles lit both north and south poles, making curtains of blue and green ripple over the globe. As the thermonuclear pressure wave spread and butted against the thermosphere, it heated the air orange, compressed it, until it touched the ground and scorched a quarter of the world.

The tiny nearby moon Malhiem cracked and shattered into a billion rocky fragments and clouds of dust.

The overpressure force subsided, and three-hundred-kilometer-per-hour winds swept over Joyous Exultation, obliterating cities and whipping tidal waves over its coastlines
— Ghosts of Onyx, Chapter 27

From this description, we know the NOVA Bomb is an unbelievably powerful weapon. It not only wiped out a massive number of Covenant ships, but literally obliterated a moon and wiped out a quarter of the surface of a inhabited planet. This is no normal nuke. A standard UNSC nuclear weapon yield is somewhere in the one to thirty megaton range, larger than anything the United States has ever built or tested, and it can’t even take down a single Covenant ship unless it is detonated from inside the ship. It is very hard to judge the yield based on the moon’s destruction since we aren’t given any information on size, but the planet was inhabited by Sangheili, so it much have been somewhere in the ballpark of the size of Earth, 0.5 to 2 times the diameter and with a similar density. Based on the depiction of cities getting wiped out, generating tidal waves, creating intense winds, and scorching a quarter of the surface, the energy released onto the surface of the planet is in the range of the size of the asteroid that is thought to have played a major factor in the extinction of the dinosaurs. That’s the amount of energy in at least tens of millions of Tsar Bombas, the largest nuclear device ever set off by man (for now). But of course that is something you just can’t wrap your mind around, so here is a video that gets the idea across a little better.


A 10 kilometer (6 mile) wide asteroid, the same size as the asteroid that hit Earth 66 million years ago, impacting Earth nearby New York City.


Of course, this is a very rough estimation since there are several factors at play here, but the big takeaway is that we know this NOVA Bomb was detonated somewhere in orbit around the planet, meaning this is just the energy remaining after it has traveled hundreds if not thousands of miles. Assuming the energy released expands in all directions equally, we can use the normal equation for the surface area of a sphere (4 · π · r²) to determine that the energy output must grow 4 times every time the distance is doubled. While we don’t know the exact distance the bomb was from the planet when it detonated, it is obvious that the explosion would have likely been hundreds of times more energetic than what hit the surface. Considering the bomb also completely destroyed Joyous Exultation’s moon, that seems like it would be a reasonable estimation.


While Ghosts of Onyx came out in 2006, we didn’t get another use of a NOVA Bomb in the lore for eleven years until Envoy was released in 2017. As an interesting side-note, while there is over a decade of time between the appearance of a NOVA Bomb in Halo media, the events were only two months apart in-universe, both at the end of 2552. We don’t get quite as much information on the devastation of a NOVA Bomb in Envoy, but it does provide a few good bits that will help us nail down a general size of this bomb.

We brought a NOVA Bomb with us...”

”Our deep-space comms equipment was damaged,” Mike said. “We never got the orders to cease or withdraw. We didn’t know the war was over, never mind that there was peace. So we followed through with SUNSPEAR and lit the nuke.”

”We got out before the destruction,” Adriana said. “We watched from orbit in our escape shuttle. An entire planet ripped apart. Every living thing on it killed in a moment. Zero probability for survival, no matter what kind of lifeform. By the end, it was just empty debris where a planet once had been. And that’s when I actually started wondering—where does this armor stop and flesh begin?
— Halo: Envoy, Chapter 12

In Ghosts of Onyx, an entire moon was ripped apart, though since we didn’t know how large the moon was, it was impossible to use this as a gauge of bomb size. In Envoy, it would appear that a NOVA Bomb, likely detonated from somewhere on the surface or within the planet, completely destroyed it. As in, it turned an entire planet around the same size as Earth into a ring of debris. I’m really struggling with accepting this description, but since the wording is pretty cut and dry, I will assume it is correct. For now.


If you are curious why I am uncomfortable with the depicted size of the NOVA Bomb, it is because it takes an absurd amount of energy to completely destroy a planet. Think about it this way: If you read my previous Fiction Science article on MAC rounds, you might remember that I wrote a lot about escape velocity of massive objects like planets and stars. The escape velocity is the speed at which an object must travel in order to never get pulled back in by the gravity of the body. Any slower than that and the object will eventually either crash back to the surface or enter orbit. To turn a planet into a cloud of debris, you would have to do that to the entire planet itself. Each piece of planetary debris would have to have enough speed to escape the gravity of all the other pieces, otherwise they would all coalesce back into a sphere again. To see just how much energy we are talking about, check out this short clip.


As you can see from this, the amount of energy required it absolutely enormous. I won’t go through the math again here since they do a better job of explaining it in the video, so I will just restate that the energy required to blow up a planet in the manner described in Envoy is 2.25 · 10³² Joules, or 225 million Yottajoules. To put that number into a perspective we can actually understand, using 382.8 Yottajoules/second for the output of the sun, that is 6.8 days of the energy from the sun, released by a bomb, in an instant, on a planet. I haven’t done the math yet, but if it takes nearly seven days for the sun to produce that much power, I have serious concerns that the bomb would have to be absurdly large.

In addition to carrying over this value to the next phase, lets look a few other numbers for comparison purposes. The first we will look at is the Chicxulub Impactor mentioned above, the large asteroid or comet that his the Earth around 66 million years ago. With an energy of 1.3 to 58 Yotta Joules, it is a lot smaller than the world destroying number above, but also much more feasible from the perspective of a bomb. Since there is such a range for estimated impact energy, we will look at both the minimum and maximum values separately.

The other comparison event we can look at is a hypothetical one, but one that some analysis has been done for, so we have some decent numbers and examples. Were a 500 kilometer-wide asteroid to impact Earth at 20 kilometers per second (kps), the resulting destruction would be unfathomable. Using an online asteroid impact calculator, we can get a rough estimate for the energy released by such an impact, 26,000 Yotta Joules. This dwarfs the Chicxulub event, though still is 10,000 times smaller than what would be required to rip Earth apart.

Before we move on, lets quickly look at all the different sizes of explosions we chose and compare their energy outputs.


Chicxulub Impact (S) 1.3 YJ 11 km
Chicxulub Impact (L) 58 YJ 80 km
Life Ender 26,000 YJ 500 km
World Destroyer 225 million YJ 10,000 km



The first phase of determining the size of a NOVA Bomb was establishing a required energy output based on the established lore. Now that we have a few good potential options, we need to convert that energy into a bomb size. Luckily, this is data that has already been established during nuclear weapons testing in the 1940s through the 1970s. Based on the good deal of data we have collected from those tests, a practical maximum yield per kilogram has been established at 6 kilotons of TNT per kilogram or 25 Terrajoules (TJ) per kg, known as the Taylor Limit. This makes our job really easy, as it is just a linear correlation between energy output and bomb size. From Ghosts of Onyx, we know that the NOVA Bomb is a series of fusion warheads, so using the Taylor Limit as our maximum yield per kilogram is a safe assumption for its size. By taking the calculated energy output in Terrajoules and dividing it by 25, the mass of each bomb can be determined using the following equations:

  • 1 Yottajoule (YJ) = 1,000,000,000,000 Terrajoules (TJ)

  • 1 metric ton (tonne) = 1,000 kilograms (kg)

  • Energy in TJ / 25,000 = Bomb mass in Tonnes

Plugging in this equation into the four scenarios we determined above, the masses for each bomb can be determined as follows:


Chicxulub Impact (S) 1.3 YJ 52 million tonnes
Chicxulub Impact (L) 58 YJ 2.3 billion tonnes
Life Ender 26,000 YJ 1 trillion tonnes
World Destroyer 225 million YJ 9 quadrillion tonnes

Again, we have more numbers that are so large that they are basically meaningless to us. To try to get some kind of grasp on these masses, we can compare it to some familiar Halo warships. Here is a sample of the sizes of a few UNSC and Covenant ships:


Pillar of Autumn 1.17 km 9 million tonnes
Spirit of Fire 2.5 km 44 million tonnes
Infinity 5.7 km 970 million tonnes
Shadow of Intent 5.3 km 2.7 billion tonnes
Long Night of Solace 29 km 3.7 trillion tonnes*
Mantle's Approach 371 km 4.7 quadrillion tonnes

*estimated mass based on similar design and size difference between Shadow of Intent and Long Night of Solace.

Its pretty obvious at this point that no matter what option we choose for the mass of the bomb, it is going to be pretty big. We will get into the actual diameter of a bomb that big in a little bit, but remember that any ship will still be mostly empty space, while our bomb is mostly just bomb. That will help our calculations a lot, so the NOVA Bomb may not be quite as unfathomably large as it is looking at the moment.

Another thing to consider before we move on is that the Taylor Limit is not a theoretical limit but a practical limit. Bombs that fall along the limit are still only around 50% efficient with respect to the amount of bomb material that is actually fused and converted to energy. There are theoretical bomb designs that are closer to 40 TJ/kg, so it wouldn’t be out of the realm of plausibility to say the NOVA Bomb is far more efficient than fusion weapons of the 20th century. Using this much more generous conversion rate for energy output to bomb mass and the same equation from the previous table, we get new values for the masses of our four examples:


Chicxulub Impact (S) 1.3 YJ 32.5 million tonnes
Chicxulub Impact (L) 58 YJ 1.4 billion tonnes
Life Ender 26,000 YJ 625 billion tonnes
World Destroyer 225 million YJ 5.6 quadrillion tonnes

These numbers aren’t orders of magnitude smaller, but they will still make our bomb considerably more manageable. One thing I have to this point ignored is the following quote from the late Admiral:

When detonated it compresses its fusionable material to neutron-star density, boosting the thermonuclear yield a hundredfold.
— Recording of Admiral Danforth Whitcomb, November 3rd, 2552

From the wording alone, I would say that we could take our original table of masses and make them one hundred times smaller. The reality is, however, that this would violate the laws of physics, primarily by making the bomb efficiency greater than 100%, more like 4000% efficient. This is, of course, impossible. The only way to get yields that large from a mass that small would be if this were an antimatter bomb, but we know from the description that this is a fusion device. I chalk this comment up to the Admiral exaggerating for effect, which is something Admiral Hood is known to have done during the Battle for Earth twice.

Before we continue, here is a quick comparison of our bomb mass examples versus the known UNSC and Covenant ship masses:





Hopefully this provides some scale to the absolutely absurd amount of nuclear material would be required to build a NOVA Bomb the size required to actually rip an Earth-sized planet into bits of planetary debris. I don’t hold a ton of confidence at the moment that the UNSC possesses the technology in 2558, let alone 2552, to build a nuclear weapon more massive than the flagship of the Forerunner fleet. I am undaunted, however, so we will continue on and determine how big each of these bombs would have to be.


While we have figured out the required mass of the different sizes of bombs, the important factor and the initial question relates to how large the NOVA Bomb must be and whether or not it is feasible for it to be built by humans and used in the manner it was in Ghosts of Onyx and Envoy. The first part of this question is going to be very hard to answer since we mostly know of the capabilities of 26th century human construction techniques through the things they have built. Considering they can build ships like the UNSC Infinity and arrays of Super MAC Orbital Defense Stations like was built around Earth, however, it would have to be a very large weapon for me to be convinced that it is totally unfeasible for it to exist in the Halo universe.

Even in the case of the Fall of Reach when Whitcomb uses the NOVA Bomb as a Trojan horse to destroy the Covenant fleet, it is just sitting on the planet and then picked up by Covenant Supercarrier Sublime Transcendence, so as long as the bomb could feasibly fit within the ship, it will pass that test.

The most difficult test to pass for the NOVA Bomb’s size is going to be its use on Glyke. Gray Team transported the NOVA Bomb to the Sangheili-populated planet, where they managed to get the device onto the planet and detonate it. While there is nothing saying Gray Team couldn’t have been towing the bomb with their prowler, it would be awfully hard to get a gigantic bomb onto the surface of a hostile planet without being noticed and successfully detonate it. I guess the only way to know is to do the math, so here it goes.


The key to determining the size of each of our reference events is going to be shape and density. We aren’t given either value, so we will have to determine them on their own. While the bomb is more than likely not a perfect sphere, this will be the easiest shape to calculate, and is close enough to the shape of most nuclear warheads that it is a good approximation.

Density, meanwhile, is harder to pin down. We know that the bomb casing is made of Lithium tritide (Lithium triteride isn’t a thing), which is just Lithium hydride with the hydrogen atoms replaced with Tritium. We also know this is a fusion device, so it is using elements low on the periodic table to generate energy. These elements unfortunately all have low density, including Lithium tritide, which has a density of 0.82 grams / cubic centimeter. Comparatively, Uranium has a density of 19.1 grams / cubic centimeter. Since we don’t know the details of the bomb internals, I will be generous and say the average density of a NOVA Bomb is 1 gram / cubic centimeter. This will also make our math a lot easier, which is always good.

To calculate the total bomb size, we will have to use the density we just determined and the bomb mass we calculated in the last section to find the total volume of the object. From there, we can figure out the diameter of a sphere of that volume. The calculations we will use are the following:


  • VOLUME = 1.33 · π · RADIUS³


Using these equations, we find the following for all four of our reference scenarios:


Chicxulub Impact (S) 32.5 million tonnes 0.0325 km³
Chicxulub Impact (L) 1.4 billion tonnes 1.4 km³
Life Ender 625 billion tonnes 625 km³
World Destroyer 5.6 quadrillion tonnes 5.6 million km³

From these calculated volumes, we can then determine the diameter of each event by assuming the bomb is a single sphere, the most efficient shape in terms of volume to diameter / width ratio.


Chicxulub Impact (S) 0.0325 km³ 0.4 km
Chicxulub Impact (L) 1.4 km³ 1.4 km
Life Ender 625 km³ 10.6 km
World Destroyer 5.6 million km³ 220 km

In the words of Neo, “Whoa”. Those are incredibly, stupendously, absurdly huge bombs. How does this compare to the length of our reference ships from earlier? (remember that the bomb is a sphere, the ship is mostly a very thin, long tube)


Pillar of Autumn 1.17 km
Spirit of Fire 2.5 km
Shadow of Intent 5.3 km
Infinity 5.7 km
Long Night of Solace 29 km
Mantle's Approach 371 km



As I feared at the onset, the sheer size of a fusion weapon with the yield described in Ghosts of Onyx and more importantly Envoy, is not scientifically plausible. Something I hadn’t considered before was that while Gray Team could have towed the Nova Bomb to Glyke instead of putting it aboard their prowler, we know the NOVA Bomb fits within the cargo hold of the Sublime Transcendence, a Covenant Supercarrier, but still only 29 km in length. The World Destroyer’s diameter is literally over 7.5 times more than the length of the ship. Even the Life Ender’s diameter is over a third the width and more than three times the height. The only remotely feasible sizes are either Chicxulub Impact events, and even the small one seems excessively large. I didn’t have great expectations going into this, but the numbers are actually worse than I thought they would be.


I am not ready to totally give up on this just yet, though. We have a few different ways to work with the numbers to make the lore and science play nice. To be clear, what lies ahead is less science and a bit more fiction, but I will do my best to stay within the realms of possibility.

The real problem here is that while the energy per atomic fusion per nucleon (amount of energy released from fusion divided by the size of the nucleus) is much higher than the energy per atomic fission per nucleon, the heavy elements are, well, heavier per atom. This manifests itself in our calculations in the density. While Uranium’s density is over 19 g/cc, the density of the light elements like Hydrogen and Helium is less than 1 g/cc. Even being generous and using 1 g/cc in our calculations, we didn’t get close to a feasibly-sized NOVA Bomb.

I see four possible solutions to this problem. We can either make the nuclear material denser, making the equivalent bomb volume smaller and thereby making the energy per unit volume higher, make the reference event smaller, meaning the NOVA Bomb wouldn’t have to be quite as large, or make the energy released larger, meaning we get more energy per unit volume again, this time by increasing the energy rather than decreasing the volume. There is also a fourth option, change the bomb type from a fusion device to an antimatter bomb, which would allow for much higher yields. I will walk through these four possibilities now.


    This seems like the simplest option, but in my opinion, it is the least feasible (and as you will see in a minute, less fun). Density is a property of all matter that is dependent on many things from temperature and pressure at formation. For elements like Carbon, this means you can create either graphite or diamond depending on how much pressure you put the material under. Even so, the difference in density between elemental carbon and diamond is only about 50% higher (2.26 g/cc to 3.51 g/cc). Lighter elements form far fewer different solid materials as well, so even getting a 50% increase in density would be hardly feasible and wouldn’t get us even close to the target yield anyway. Unless you invent new physics, substantially increasing the density of the nuclear material isn’t a plausible explanation, and I would like to stay closer to science than fantasy.


    The easiest way to make the numbers work out is to simply make the NOVA Bomb’s explosive yield smaller. Scientifically this would work out just fine, though it would end up flying in the face of established lore by a wide margin. As we concluded above, even the second smallest of the four options is really pushing the limits of the maximum size of a NOVA Bomb, and that option is basically the amount of energy that is described to have reached the surface of Joyous Exultation, which we know has to be much smaller than the total yield of the weapon. Even ignoring the description in Ghosts of Onyx, a Chicxulub-sized bomb would simply not fit the description at all in Envoy, which we know made the entire planet devoid of life and killed billions, not to mention the part that strongly implies it obliterates the entire planet.

    As a small aside, when I began researching this topic, I thought the ‘Life Ender’-sized event was was more in the ballpark of the size the NOVA Bomb should be based on the description, but when I read through the actual wording, I got stuck on one line in particular, “By the end, it was just empty debris where a planet once had been.” The rest of the wording is vague enough that it can be argued the planet itself wasn’t completely destroyed like Alderaan, but this line sticks out to me because it doesn’t give much wiggle room. It could be chalked up to poetic license on the part of Adriana, but I hate falling back on ‘he/she was mistaken’ arguments to clear up lore inconsistencies. We may just have to do that here though. For a visual reference, here is what the ‘Life Ender’ NOVA Bomb would do to a planet the size of Earth:


“It would be as if the sun had come to Earth.” This is exactly what I had in mind when I pictured a NOVA Bomb.


A chart of the binding energy of various elements on the periodic table.


    One thing mentioned in passing at the end of my article on Element 121 and the feasibility of the science behind Nightfall was that perhaps I had stumbled upon an idea for how the Pillar of Autumn’s self destruction was powerful enough to destroy Alpha Halo. While a Halo is significantly smaller than the Earth as I described several months ago, it would still take an incredibly large explosion to break a Halo apart. My theory was that perhaps a Wildcat destabilization of the Autumn’s core meant that the reactor went through a process similar to what happens at the end of a star’s life and essentially went supernova. This might, in theory, account for the seemingly impossibly large explosion and destruction of the ring.

    Perhaps the same process is going on here. To explain as simply as possible, every fusion of two elements below Iron on the periodic table, and every fission of an element above Iron will result in a release of energy. In a star, it begins life by fusing Hydrogen atoms together to create Helium. After a while, there is enough Helium and the star is hot enough to begin fusion of Helium. This process continues (very oversimplified, but you get the gist) through the higher and higher elements until the star reaches Iron. When Iron is fused together, it actually takes away energy from the star, beginning the collapse of the entire thing until it all smashes together in the middle and explodes as a supernova.

    When we are talking about the yield of fusion weapons, we are talking about a single fusion event, such as Hydrogen with Hydrogen, Hydrogen with Helium, or something along those lines. If scientists were somehow able to make a bomb that compressed to the point where all the fusionable material fused not once but several times until it became Iron, you could get a yield larger than just from a single set of fusions. Doing the math, however, this would only net us maybe a 20% increase in total yield, so while it does help out a little bit, decreasing volume 20% isn’t going to turn either the Life Ender or World Destroyer into feasible nuclear weapons. This also kills my theory about just how the Autumn’s reactor detonation broke up a Halo, which is unfortunate.


    This one is probably the most plausible from a science standpoint, at least in terms of not violating basic laws of physics. While chemical reactions convert no mass into energy, fission converts 0.1% into energy, and fusion converts 0.7% into energy, the matter-antimatter reaction converts 100% of its mass into energy. This is because, from a matter standpoint, matter and antimatter are like two waves 180° out of phase with each other. They cancel out and become pure energy. As you can probably see just from the percentages, an antimatter bomb would be over 100 times smaller in terms of volume than a fusion weapon of equivalent yield. Without even doing the math, its apparent that this would definitely make the Life Ender-sized bomb more feasible to transport, and possibly even the World Destroyer.

    The biggest problem with this theory is that it makes Admiral Whitcomb’s speech describing the inner-workings of the bomb total nonsense. There are a couple of fairly easy ways to retcon this away, and while I don’t like retcons in general, I think they work well enough in this case. The first option is that Whitcomb said this to throw off any Covenant that might understand him so that it would disrupt any attempt to dismantle the bomb. The second is that Whitcomb is like that boss who tries to explain your work to upper management but doesn’t have a grasp on what the heck it is you did so he just makes some crap up. He may have understood the bomb is 100 times more powerful than a fusion weapon and heard something about “neutron star density” and filled in the rest with nonsense. Neither are great explanations, but I far prefer them over the bomb working on ‘space magic’.



We have been as this analysis for a long while not, so I will try to get to the point as quickly as possible. Of the options above, we only have a couple viable scenarios. Either the bomb is some version of a fusion device and the yield is far smaller than described, the bomb is an antimatter bomb of some type instead of the fusion device as described, or it is exactly as described and ‘space magic’. I don’t like the third option at all and it also can’t be analyzed scientifically to any degree, so I am going to ignore it. The other two require a retcon of some kind, though the antimatter one requires the more plausible one in my opinion. Here are our two remaining options:


    Using every bit of possible energy we could maybe extract from a fusion reaction as described above, the maximum energy output per kilogram of bomb is about 120% of what we determined before. Originally we said the assumed bomb yield was 40 TJ / kg, so at 120% yield, that is 48 TJ / kg. This isn’t going to be nearly enough to get us where we want to be yield-wise without making a bomb so large it wouldn’t fit in a Covenant ship, so we will have to cap the size and find the largest possible yield based on that.


    This is not very different from the first option, except with a lot more energy per kilogram. Per Wikipedia, 4.184 TJ is equivalent to 46.55 mg of matter, which comes to about 90,000 TJ / kg, nearly 2,000 times more than the same sized fusion reaction. In reality (or as close an approximation as we can get), a large portion of that energy wouldn’t be in the form of explosive kinetic energy, but rather in things like neutrinos which for all intents and purposes do not react with normal matter. The conversion rate from matter to usable explosive energy would be maybe 50%, which is about 45,000 TJ / kg.

    One other thing we need for this calculation is density. There is no scientific reason why you couldn’t make something like anti-Tungsten with a very high density, but doing so would be incredibly difficult. All known ways of creating antimatter make things like anti-protons and anti-electrons, which you would then have to combine to make the anti-Tungsten. This is like taking hydrogen and fusing it together until you get Tungsten. The effort required to do that to antimatter where it cannot interact with regular matter or else it explodes is beyond what I would consider feasible. For consistency and simplicity I will use the same 1 g/cc density we are using for the fusion bomb.

Even a 0.2 km diameter spherical bomb would be two football fields wide, tall, and deep. That already seems beyond feasible, but given construction in space and a hefty bit of generosity, lets use that as the largest the bomb could be. Based on a 0.2 km diameter bomb, the maximum yields of each bomb is now:


Fusion (original) 40 TJ/kg 0.17 YJ
Fusion (enhanced) 48 TJ/kg 0.2 YJ
Antimatter (50% eff) 45,000 TJ/kg 188.5 YJ
Antimatter (100% eff) 90,000 TJ/kg 377 YJ

Comparing these against the reference asteroid impacts from the beginning, we can see how close they are.


Chicxulub Impact (S) 11 km 1.3 YJ
Chicxulub Impact (L) 80 km 58 YJ
Life Ender 500 km 26,000 YJ
World Destroyer 10,000 km 225 million YJ

Without even plotting the largest two reference impacts (and the only two that would feasibly fit into the descriptions given for the effects of a NOVA Bomb), it is apparent a 0.2 km diameter bomb isn’t going to cut it. Not even close. At this point I am about ready to declare this entirely fiction, but before we completely give up, lets see how large an antimatter bomb would have to be to match the destruction of either the Life Ender or the World Destroyer.


Life Ender 26,000 YJ 1.03 km
World Destroyer 225 million YJ 21.2 km

So we are in a bit of a tight spot. A 1.03 km diameter is a lot better than the 10.6 km we got originally, but it is still kind of an impossibly large bomb. For one, we are making at least two retcons, first that the bomb isn’t a fusion device but an antimatter bomb, and second that the NOVA Bombs destructive power cannot actually rip a planet apart, but ‘merely’ turn it into a molten ball of death. Then we have to consider that this antimatter bomb had to sit on the surface of Reach without exploding, would still somehow have to fit within the cargo bay of a Covenant Supercarrier, and would have had to have been towed by Gray Team rather than transported within their prowler.



When I began putting this topic together, I really thought it would work out with some minor consolations. After eking out every possible bit of energy from the known universe and giving every benefit of the doubt to the lore, however, I just cannot make the numbers work out. As a fusion device like is described in Ghosts of Onyx, the destruction would either have to be far far smaller than is described in either Ghosts of Onyx or Envoy, or the bomb (212 km diameter / 5.6 quadrillion tonnes) would have to be far larger than the Infinity (5.7 km long) and more massive than even Mantle’s Approach (4.6 quadrillion tonnes). That is of course assuming you could even make a fusion device that size work, which is effectively impossible. As an antimatter device the bomb becomes far smaller, but even including a lowering of the required yield, with a diameter (1.03 km) close to the length of the Pillar of Autumn (1.17 km) and a mass (578 million tonnes) over thirteen times more than the UNSC Spirit of Fire (44 million tonnes), it is still well beyond anything I am willing to consider plausible.

Since we have exhausted all scientific explanations for the scale of the NOVA Bomb, we are free to explore some more fantastical in-universe explanations. Perhaps it utilizes Slipspace somehow to enhance the yield, or it harnesses vacuum energy like Forerunner structures do, or we can just say the Precursors did it. If I had to pick one I would probably take the first option, though I will let you make your own head-canon on this one. I don’t want to end the article on a down-note though, so here is a simulation (obviously) of the largest impact event the Earth has ever experienced, the Mars-sized object that struck over 4.5 billion years ago and formed the Moon, an event that is still orders of magnitude smaller than the power of a NOVA Bomb.



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