Kurzgesagt – In a Nutshell
Kurzgesagt – In a Nutshell
Embedded Files
Sources – Killer Asteroid
Sources – Killer Asteroid
We thank the following experts for their comments:
Professor Philip Lubin
UC Santa Barbara
Alexander “Sasha” N. Cohen
UC Santa Barbara
Brin Bailey
UC Santa Barbara
For more information on their “PI: Pulverize It/Penetrator Interceptor” project, check out their webpage:
#UCSB Experimental Cosmology Group: “PI-Multimodal Planetary Defense”
https://www.deepspace.ucsb.edu/projects/pi-terminal-planetary-defense
Which includes the following paper where they cover the more technical details:
#Lubin, Philip (2021): “Multimodal Planetary Defense”
https://www.deepspace.ucsb.edu/wp-content/uploads/2024/10/PI-Terminal-Defense.pdf
—Even at this moderate size, a fireball brighter than the Sun will tear through the atmosphere at 60 times the speed of sound and the destructive power of 4,000 Hiroshima bombs flattens cities, killing millions.
We are considering the case of the impact of a 100 m asteroid traveling at around 20 km/s.
The brightness of the hypothetical asteroid is speculative, but possible as the asteroid approaches if it has a reflective enough surface.
#Encyclopedia Britannica: “Speed of sound” (retrieved 2025)
https://www.britannica.com/science/speed-of-sound-physics
20 km/s / 0.331 km/s = 60.4
We choose an approximately spherical asteroid of density 2.3 g/cm3, corresponding to the mean density of CM carbon chondrites
#Carry, Benoit (2012): “Density of asteroids”, Planetary and Space Science, vol. 73
https://www.researchgate.net/publication/221719653_Density_of_asteroids
Quote: “Table 2: Average bulk density (ρ) measured on Ns sample of Nm meteorites
used in Table 1: Ordinary chondrites (OC: H, L, and LL), Carbonaceous chondrites (CC: CI, CM, CR, CO, CV, and CK), Enstatites chondrites (EH and EL), Achondrites HED (i.e., average of Howardites, Eucrites, and Diogenites), Stony-Iron (Pallasites, Mesosiderites, and Steinbach), and Iron meteorites (Ataxites and Hexahedrites). Terrestrial weathering has a strong effect on the porosity of found OCs with respect to fallen OCs (Consolmagno et al. 2008). Only measurements on falls are therefore used here. For the other meteorite classes, both finds and falls are used. The density of liquid water of 1.00 ± 0.10 is used as a proxy for the volatiles that compose icy bodies. References: (1) Consolmagno and Britt (1998). (2) Britt and Consolmagno (2003), (3) Consolmagno et al. (2008), (4) Macke et al. (2010), and (5) Macke et al. (2011).”
This gives us a total mass for the asteroid of:
m = (4𝜋 (D/2)3/3) × ⍴ = (4𝜋 (100 m /2)3/3) × 2,300 kg/m3 = 1.2 × 109 kg
And thus a kinetic energy of:
E = mv2/2 = (1.2 × 109 kg) × (20,000 m/s)2 /2 = 2 × 1017 J = 6 × 107 ton of TNT
We take an approximate yield of 15,000 tons of TNT for the bombing of Hiroshima.
#USDE: The Manhattan Project, an Interactive Story: The Atomic Bombing of Hiroshima” (retrieved 2025)
https://www.osti.gov/opennet/manhattan-project-history/Events/1945/hiroshima.htm
Lastly:
6 × 107 ton of TNT / 15,000 ton of TNT ~ 4,000
—In 2019, asteroid OK, big as a 30-story building, was discovered just one day before it grazed earth closer than some of our satellites.
#NASA: “2019 OK” (retrieved 2025)
https://science.nasa.gov/solar-system/asteroids/2019-ok/
#Zambrano-Marin, Luisa Fernanda et al. (2022): “Radar and Optical Characterization of Near-Earth Asteroid 2019 OK”, The Planetary Science Journal, vol. 3, 6
https://iopscience.iop.org/article/10.3847/PSJ/ac63cd/pdf
Quote: “We conducted radar observations of near-Earth asteroid 2019 OK on 2019 July 25 using the Arecibo Observatory S-band (2380 MHz, 12.6 cm) planetary radar system. Based on Arecibo and optical observations the apparent diameter is between 70 and 130 m. [...]
Near-Earth asteroid (NEA) 2019 OK was discovered on 2019 July 24 by Cristovao Jacques, Eduardo Pimentel, and Joao Ribeiro de Barros at Brazil’s Southern Observatory for Near Earth Asteroids Research (SONEAR) shortly before its closest approach to Earth. [...] The object’s orbital information from the JPL Small-Body Database shows the closest approach was on 2019 July 25 01:22 TDB at a distance of 11.2 Earth radii (0.00048 au) from Earth, approaching the planet at a relative velocity of 24.53 km s–1.”
Assuming that the asteroid’s diameter is the mean of its lowest and highest possible diameters, and that a storey is around 3 m, the 2019 OK asteroid had a height of:
(130 m + 70 m) / (2 × 3 m) = 33 storeys
Its closest approach, at 11.2 Earth radii, is closer to Earth than even the closest part of the orbit of some artificial satellites.
#NASA HEARSAC: “What is TESS?” (retrieved 2025)
https://heasarc.gsfc.nasa.gov/docs/tess/what-is-tess.html
Quote: “The nominal perigee and apogee of the elliptical orbit are 17 Earth radii and 59 Earth radii, respectively.”
—Last year, the even larger asteroid MK was spotted only 13 days before it passed us closer than the Moon.
#ESA (2024): “Close approach of asteroid 2024 MK”
https://www.esa.int/ESA_Multimedia/Images/2024/06/Close_approach_of_asteroid_2024_MK
#NASA: “Moon Facts” (retrieved 2025)
https://science.nasa.gov/moon/facts/
Quote: “The Moon is an average of 238,855 miles (384,400 kilometers) away. That means 30 Earth-sized planets could fit in between Earth and the Moon.”
—If they had hit Earth, they would have unleashed the destructive power of 3,000 and 9,000 Hiroshima bombs.
2019 OK had an approximate diameter of 100 m and an approximate density of 1 g/cm3. It approached Earth at 24.53 km/s.
#Zambrano-Marin, Luisa Fernanda et al. (2022): “Radar and Optical Characterization of Near-Earth Asteroid 2019 OK”, The Planetary Science Journal, vol. 3, 6
https://iopscience.iop.org/article/10.3847/PSJ/ac63cd/pdf
Quote: “We conducted radar observations of near-Earth asteroid 2019 OK on 2019 July 25 using the Arecibo Observatory S-band (2380 MHz, 12.6 cm) planetary radar system. Based on Arecibo and optical observations the apparent diameter is between 70 and 130 m. [...]
The object’s orbital information from the JPL Small-Body Database shows the closest approach was on 2019 July 25 01:22 TDB at a distance of 11.2 Earth radii (0.00048 au) from Earth, approaching the planet at a relative velocity of 24.53 km s–1.[...]
We obtained ρbulk = 1.2 g cm-3 for D = 70 m with a porosity of 0.6, and ρbulk = 0.8 g cm−3 for a 130 m object with a porosity of 0.8.”
This gives us a mass of:
m = (4𝜋 (D/2)3/3) × ⍴ = (4𝜋 (100 m /2)3/3) × 1,000 kg/m3 = 5.2 × 108 kg
And thus a kinetic energy of:
E = mv2/2 = (5.2 × 108 kg) × (24,530 m/s)2 /2 = 1.6 × 1017 J = 3.8 × 107 ton of TNT
We take an approximate yield of 15,000 tons of TNT for the bombing of Hiroshima.
#USDE: The Manhattan Project, an Interactive Story: The Atomic Bombing of Hiroshima” (retrieved 2025)
https://www.osti.gov/opennet/manhattan-project-history/Events/1945/hiroshima.htm
Lastly:
3.8 × 107 ton of TNT / 15, 000 ton of TNT ~ 3,000
2024 MK is approximately 190 m in diameter.
#ESA (2024): “Close approach of asteroid 2024 MK”
https://www.esa.int/ESA_Multimedia/Images/2024/06/Close_approach_of_asteroid_2024_MK
It approached Earth at 9.4 km/s
#ESA: “Close approach fact sheet for asteroid 2024 MK” (retrieved 2025)
It has a composition similar to an L-ordinary chondrite, whose mean density is 3.4 g/cm3.
#McGraw, Lauren E. et al. (2024): “Comprehensive Study of Near-Earth Asteroid 2024 MK: Testing Planetary Encounters as a Source for Surface Refreshing”, The Astrophysical Journal Letters, vol. 977, 1
https://iopscience.iop.org/article/10.3847/2041-8213/ad9728
Quote: “2024 MK is an S-type asteroid that is compositionally most analogous to an L-ordinary chondrite.”
#Carry, Benoit (2012): “Density of asteroids”, Planetary and Space Science, vol. 73
https://www.researchgate.net/publication/221719653_Density_of_asteroids
Following the same reasoning as before:
m = (4𝜋 (D/2)3/3) × ⍴ = (4𝜋 (190 m /2)3/3) × 3,400 kg/m3 = 1.2 × 1010 kg
E = mv2/2 = (1.2 × 1010 kg) × (9,400 m/s)2 /2 = 5.4 × 1017 J = 1.3 × 108 ton of TNT
108 ton of TNT / 15, 000 ton of TNT ~ 9,000
—Scientists have devised all kinds of tricks to push dangerous asteroids away – painting it so sunlight will deflect it, landing thrusters to steer it, scorching it with lasers, or even crashing a whole spacecraft into it.
#Khiavi, Sajjad Aslani; Jafari-Nadoushan, Mahdi (2025): “Efficient approach of painting asteroids for planetary defense using network data envelopment analysis”, Advances in Space Research, vol.75, 3
https://www.sciencedirect.com/science/article/abs/pii/S0273117724010883?via%3Dihub
Quote: “Katz investigated the possibility of changing the asteroid's orbit by coating the surface with a reflective metal to change the Sun's radiation pressure force on it. This problem was similar to the Yarkovsky effect (Hyland et al., 2010a, Hyland et al., 2010b, Daly et al., 2017), but it is different in that it depends on the instantaneous force of the radiation pressure. In Katz's research, the effects of radiation pressure force and albedo changes on asteroid orbits are considered.”
#Chapman, Clark R.; Durda, Danial D. (2001): “The Comet/Asteoir Impact Hazard: A Systems Approach”
http://www.disastersrus.org/emtools/spacewx/NEOwp_Chapman-Durda-Gold.pdf
Quote: “If one could dock-and-push with the high impulse thrust of a chemical rocket, a variety of cases could be dealt with. The Space Shuttle main engine could just deflect a 1 km asteroid, given 30 years advance warning. A Delta 2 first stage, with a several-minute burn, could deflect a 100 m object given 6 months warning”
#Cheng, Qinkun; Zhang, Wei (2024): “Scientific issues and critical technologies in planetary defense” ,Chinese Journal of Aeronautics, vol. 37, 11
https://www.sciencedirect.com/science/article/pii/S1000936124002590?via%3Dihub#s0055
Quote: “Laser Ablation (LA): Phipps et al. first mentioned the use of LA technology to alter the orbit of objects in space in 1994.243 LA is a possible low thrust technology that can be used for noncontact deflection and manipulation of PHOs. It uses a laser light source to illuminate the PHO surface, and absorb the heat of the laser beam, allowing the irradiated materials to directly sublimate from solid to gas. The sublimated materials form the eroded ejects. Similar to rocket exhaust, the flow of ablative materials generates continuously controlled low thrust. This slow thrust can be utilized to alter the PHO trajectory and rolling motion, pushing it away from Earth.”
#Rivkin, Andrew S.; Cheng, Andrew F. (2023): “Planetary defense with the Double Asteroid Redirection Test (DART) mission and prospects”, Nature Communications, 14, 1003
https://www.nature.com/articles/s41467-022-35561-2
Quote: “The history of life on Earth has been dramatically influenced by asteroid impacts. Tens of thousands of objects larger than 140 meters, capable of causing regional destruction, orbit the Sun in near-Earth orbits, but less than half have been found. A variety of mitigation techniques have been considered in case an incoming object is ever detected. One such technique, the kinetic impactor, is conceptually simple: A spacecraft is purposefully collided with the asteroid of concern, and the addition of the spacecraft momentum alters the asteroid orbit so that it no longer hits the Earth.”
—But it turns out, most of them aren’t like that. They are more like bags of loosely packed gravel – heaps of pebbles, precious minerals and dust, barely held together.
#Hestroeffer, Daniel; et al. (2019): “Small Solar System Bodies as granular media”, The Astronomy and Astrophysics Review, vol.27, 6
https://link.springer.com/article/10.1007/s00159-019-0117-5
Quote: “In contrast to large telluric planets and dwarf planets, a large proportion of [asteroids and small solar system bodies (SSSBs)] is believed to consist of gravitational aggregates (‘rubble piles’) with no—or low—internal cohesion, with varying macro-porosity and surface properties (from smooth regolith covered terrain, to very rough collection of boulders), and varying topography (craters, depressions, ridges). Bodies with such structure can sustain some plastic deformation without being disrupted in contrast to the classical visco-elastic models that are generally valid for planets, dwarf planets, and large satellites. These SSSBs are hence better described through granular mechanics theories, which have been a subject of intense theoretical, experimental, and numerical research over the last four decades”
—Asteroids can approach Earth at 70,000 km/h – enough to cross the Atlantic in 5 minutes. No bomb we’ve ever made could survive such an impact. So if we go for a head-on collision, the asteroid will wreck the nuke before it even has a chance to explode.
70,000 km/h is equivalent to around 20 km/s. Asteroids approach Near Earth Space with velocities of up to 30 km/s, though most of them have lower velocities with the maximum being of around 7.5 km/s.
#Zolotarev, R.; Shustov, B. (2024): “On the parameters of encounters of NEOs with the Earth”, Modern astronomy: from the Early Universe to exoplanets and black holes. Special of the Astrophysical Observatory of the Russian Academy of Sciences, 675-680.
https://sao.editorum.ru/en/nauka/conference_article/11945/view
Quote: “Figure 3 shows the distribution of the velocity of approach, i.e. the rate of change of distance from an asteroid entering the NES to the Earth. The maximum of the distribution is at approximately 7.5 km/s (the value of the total spatial velocity is obviously higher). Of course, with further approach to the Earth the velocity of approach will increase. A very small proportion of asteroids entering the NES approach the Earth at a velocity of more than 30 km/s.”
We consider a width of around 5,000 km for the Atlantic Ocean:
#UNESCO Ocean Literacy Portal: “Atlantic Ocean basin: a Detailed Map”
https://oceanliteracy.unesco.org/atlantic-ocean/
Quote: “Its width varies considerably from north to South: about 4,830 kilometres (3,000 mi) between North America and northern Africa to 2,848 kilometres (1,770 mi) between Brazil and Liberia.”
So an asteroid traveling at 20 km/s would cross the Atlantic in:
5000 kilometres / 20 km/s = 250 s ~ 4 min
On screen, we show a journey between London and New York across the Atlantic. These two cities are approximately 5,580 km apart.
By the same calculation:
5580 kilometres / 20 km/s = 279 s ~ 4.5 min
—Ok easy, let’s explode the bomb before it touches the asteroid. Scientists have estimated the optimal distance, which for our 100 m killer friend would be a few tens of meters above the surface. Launch, set the timer and…
#Cheng, Qinkun; Zhang, Wei (2024): “Scientific issues and critical technologies in planetary defense” ,Chinese Journal of Aeronautics, vol. 37, 11
https://www.sciencedirect.com/science/article/pii/S1000936124002590?via%3Dihub#s0055
Quote: “For the [sandoff nuclear detonation] strategy, a nuclear device will be detonated near the PHO, and the high-speed neutrons and rays generated by the explosion will irradiate the regolith material on the PHO surface. Then, they can make the external surface material of the PHO evaporate, expand, and eject, causing recoil on the PHO itself. In most cases, neutrons cause more asteroids to peel off (eject or evaporate) more material than rays. Their function is similar to rocket propulsion, thereby changing the PHO orbit. Thus far, research has shown that the standoff distance may be between 20 and 300 m.”
#Ahrens, Thomas J.; Harris, Alan W. (1992): “Deflection and fragmentation of near-Earth asteroids”, Nature, vol.360, 429-433
Quote: “Figure 3. Sketch of the use of nuclear explosive radiation to induce a (~1 cm s⁻¹) velocity perturbation in a NEO. (a) Nuclear explosive designed to provide a substantial fraction of its yield as energetic neutrons and gamma rays is detonated at an optimum height (√2 – 1)R, above an asteroid (see Appendix)”
For the case of our 100 m asteroid:
(100 m / 2) × (sqrt(2) -1) ~ 20 m
—The explosion has made a dramatic crater and… nothing else. The rock will still hit us in two weeks, only a few meters to the left. Unfortunately, in space there is no air to carry a shockwave, so most of the explosion's energy is just lost.
We thank our expert Philip Lubin for the following comment:
Quote: “First, deflection of such a threat on such a short notice would require a significant change in momentum. In order for the asteroid to miss the Earth in 2 weeks, we would need to deflect it with a velocity of over 5 m/s which is orders of magnitude larger than the typical deflection speeds considered for nuclear standoff mitigation (typically a few cm/s). Second, there are immensely complex logistical and political issues associated with the use of nuclear explosive devices in general. Even if an NED were put aside specifically for use in planetary defense, it would make far more logistical sense to use a passive mitigation capability if it was also at-the-ready and had the same mitigative capability.”
—Ok let’s go the movie route – land someone on the asteroid, drill a hole and bury a nuke inside to avoid all of these problems! And indeed this is possible in theory, albeit suicidal in practice.
Many missions have successfully landed and drilled solar system objects, including smaller objects like comets.
#Zhang, Tao et al. (2017): “Drilling, sampling, and sample-handling system for China's asteroid exploration mission”, Acta Astronautica, vol. 137, 192-204
https://www.sciencedirect.com/science/article/abs/pii/S009457651631270X
Quote: “Drilling and sampling are highly efficient methods for exploring subsurface regolith and have played an important role in the search of extraterrestrial lives in recent decades [5]. Ever since the first automated drilling and samples return mission was completed in 1970 by the Soviet Union's robotic Lunar 16 lander, the drilling sampler has been widely used [6], [7]. The Apollo Lunar Surface Drill was deployed by the American astronauts to extract regolith column samples in the Apollo 15–17 missions [8]. In Soviet Union's Venera exploration projects, a drill head was first employed to drill the regolith of Venus, and the drilled cuttings were collected for in situ analysis [9]. The sampler, driller, and distribution system (SD2) was developed in 2001 by the European Space Agency (ESA) for the comet exploration mission Rosetta [10], [11], [12], [13], [14]. The Curiosity rover, equipped with the Mars Science Laboratory drill to collect Martian rocks and sand, successfully landed on Mars in 2012 [15], [16], [17], [18], [19].”
However, all these missions took years to prepare, and the drilling took a small amount of materials that were used as samples for scientific studies, not the much bigger amount that would be needed to bury a nuclear weapon.
—Landing on any space body is a nightmare. Even on on fairly Mars, a planet whose surface we know almost perfectly, roughly 70% of our attempts have failed.
#Rolfo, Daniele (2015): “High-performance hardware accelerators for image processing in space applications” (Doctoral thesis)
https://iris.polito.it/handle/11583/2616951
Quote: “Mars is a hard place to reach. While there have been many notable success stories in getting probes to the Red Planet, the historical record is full of bad news. The success rate for actually landing on the Martian surface is even worse, roughly 30%. This low success rate must be mainly credited to the Mars environment characteristics. In the Mars atmosphere strong winds frequently breath. This phenomena usually modifies the lander descending trajectory diverging it from the target one. Moreover, the Mars surface is not the best place where performing a safe land. It is pitched by many and close craters and huge stones, and characterized by huge mountains and hills (e.g., Olympus Mons is 648 km in diameter and 27 km tall).”
—Even if we succeed, drilling in microgravity is painfully slow, since there is no downward pull to help you. So we’d need an agonizing amount of time that we won’t have.
#Zhang, Tao et al. (2017): “Drilling, sampling, and sample-handling system for China's asteroid exploration mission”, Acta Astronautica, vol. 137, 192-204
https://www.sciencedirect.com/science/article/abs/pii/S009457651631270X
Quote: “Sampling an asteroid is far more difficult than sampling the Moon or Mars because the gravity of an asteroid is too small to provide the reaction force caused by the sampling action. In addition, asteroids do not have an atmosphere for heat preservation; thus, the temperature of an asteroid is much lower than that of other planets such as Mars. Therefore, the sampling method for an asteroid is more complicated.”
Even the most recent prototypes to drill asteroids can only dig a few millimeters per minute:
#Quan, Qiquan et al. (2023): “An Ultrasonic Drilling System for Fast Drilling Speed With Uncertain Load”, IEEE/ASME Transactions on Mechatronics, vol. 28, 3, 1477-1487
https://ieeexplore.ieee.org/document/9997144
Quote: “Our results show that when the temperature range is −60 to 120 °C and the rock strength is 200 MPa, the drilling speed is 8–28 mm/min, and the power consumption is less than 50 W, the stable working time of a single operation exceeds 2 min. Herein, we provide a technical reference for the application of ultrasonic drilling in planetary exploration.”
—Our cosmic bullets are called “penetrators”. A few meters long, slim and made of tungsten, a metal way denser and harder than rock. They work in an extremely simple way: You just put the penetrators the way of the asteroid, floating silently in space. From the perspective of the asteroid, you wouldn’t see a few tiny bullets sitting still. You’d see them rushing at you at 70,000 km/h!
#Lubin, Philip (2021): “Multimodal Planetary Defense” (retrieved 2025)
https://www.deepspace.ucsb.edu/wp-content/uploads/2024/10/PI-Terminal-Defense.pdf
Quote: “The proposed system uses an array of penetrating disassembly rods (PDR) to pulverize and gravitational disassembly of the asteroid. PI stands for “Pulverize It” or “Penetrator Interceptor”. Since the asteroid is moving faster than achievable by chemical propulsion, there is only modest gain to be added from the rocket speed relative to Earth compared to the asteroid speed relative to Earth. In a sense, we “just get in front of the asteroid” and wait for it to hit the penetrators rather than trying to “hit the asteroid” at high speed.”
The authors consider the penetrators to be made out of tungsten in their simulations
#Lubin, Philip; Cohen, Alexander “Sasha” N. (2023): “Asteroid interception and disruption for terminal planetary defense”, Advances in Space Research, vol. 71, 3, 1827-1839
https://www.sciencedirect.com/science/article/pii/S0273117722009395#s0010
Quote: “A 10:1 aspect ratio 100 kg cylindrical tungsten penetrator impacting at 20 km/s is used as the baseline projectile.”
The high density of tungsten and the high hardness of tungsten carbide are well known and important for its military applications:
#Advanced Refractory Metals (2024): “What are the Military Applications of Tungsten?”
https://www.refractorymetal.org/what-are-the-military-applications-of-tungsten.html
Quote:
“High Density: Tungsten is also an incredibly dense metal. At 19.3 g/cm3, it is about as dense as gold, and both metals also melt at similar temperatures.
Hardness: Tungsten is also an incredibly hard metal. It has a Mohs hardness number of 9. Only diamond is harder than tungsten carbide. Its hardness makes it a beneficial component of military armor and armor-piercing rounds, among other things.”
#Lubin, Philip: “PI—Terminal Planetary Defense Talk” (retrieved 2025)
https://www.deepspace.ucsb.edu/wp-content/uploads/2021/10/PI-Lubin-l.pdf
—We can’t destroy it too close to Earth because its fragments will slam into the atmosphere at once with the power of thousands of nuclear bombs. Our atmosphere can absorb isolated chunks – But if thousands of them strike together, their shockwaves will add up and kill millions.
#Lubin, Philip (2021): “Multimodal Planetary Defense” (retrieved 2025)
https://www.deepspace.ucsb.edu/wp-content/uploads/2024/10/PI-Terminal-Defense.pdf
Quote: “A 100m diameter asteroid would cause significant damage to a populated area if struck. In general, a 100m diameter asteroid that was intact would hit the ground and cause a very large area of destruction. At a typical 20km/s, the energy of such a bolide would be of order 100Mt. For comparison, the largest thermonuclear weapon ever tested was the Czar Bomba, with a yield of around 50Mt. We show the results of a number of simulations using our method to fragment the parent bolide into 1000 fragments, each of which has an average diameter of 10m.[...]
We chose a simulation to show a relatively rare event in overlapping blast waves from different fragments, as is seen in the first two blast waves to “hit” the observer. Note that even in this relatively extreme mitigation of 1.2 days prior to impact, there is virtually no damage as very few of the blast waves at the observer are above 1kPa where residential glass breakage begins. When we include blast wave caustic formation we find some small fraction of cases with overlapping “2 point caustics” with pressures that are about 2x higher in these small fraction of spatial locations”
We thank our expert Sasha Cohen for the following comment:
Quote: “Please note that for the 100 m case, we DO expect all of the fragments to enter the Earth's atmosphere for a mitigation 1 day prior to impact. The key to effectively mitigating the threat AND allowing the fragments to enter the atmosphere is the spread of those fragments prior to impact, which distributes the energy both spatially and temporally.”
—So instead we need to get it one day before impact, when the asteroid will be nearly 2 million kilometers away, more than 4 times further than the Moon.
The asteroid in our example moves at 20 km/s. To stop it one day before impact, we have to catch it at a distance of:
20 km/s × (24 × 60 × 60s) ~ 1.7 × 106 km
Compared to the Moon's orbit:
1.7 × 106 km / 0.4 × 106 km = 4.25
#NASA: “Moon Fact Sheet” (retrieved 2025)
https://nssdc.gsfc.nasa.gov/planetary/factsheet/moonfact.html
—A vast distance, but doable. Our current rockets can cover this in about a week.
#Lubin, Philip (2021): “Multimodal Planetary Defense” (retrieved 2025)
https://www.deepspace.ucsb.edu/wp-content/uploads/2024/10/PI-Terminal-Defense.pdf
Quote: “Due to the Earth’s significant gravitational well, the launch of payloads to targets at lunar and greater distances is vastly more difficult than launching to LEO. Launchers suitable for carrying payloads to the moon and beyond are often characterized by their “characteristic energy” which is designated as C3, given in units of (km/s)2 and is a function of the payload mass being lifted. The square root of C3 is the residual speed at infinite distance from the Earth and hence C3=0 is the minimum requirement for escaping the Earth [...]
Note that while the Space X Falcon 9 is outstanding at lifting payloads into LEO, it has a modest (but positive) C3 as it was not designed for deep space missions. The Falcon 9 Heavy has significantly higher lift and larger C3 capability than the normal Falcon 9 and both are candidates for interceptors.”
#Lubin, Philip; Cohen, Alexander “Sasha” N. (2023): “Asteroid interception and disruption for terminal planetary defense”, Advances in Space Research, vol. 71, 3, 1827-1839
https://www.sciencedirect.com/science/article/pii/S0273117722009395?via%3Dihub
From the previous graph, we see that the characteristic energy of the Reusable Falcon 9 Heavy with a payload of 2.5 tonnes (the weight of the penetrator) is around 20 (km/s)2. This means that,very far from Earth, its speed would be of around:
sqrt(20) ~ 4.5 km/s.
From the previous section of this document we have that the intercept happens 1.7 × 106 km away from Earth. This is the distance the spacecraft needs to cover. It would take it very roughly
1.7 × 106 km/ (4.5 km/s) = 380 000 s ~ 4 days 9 hours
The specific timing for our hypothetical rocket, which would best resemble Falcon 9 has been confirmed in private communications with experts Philip Lubin, Sasha Cohen and Brin Bailey.
—The asteroid crashes into the penetrator so fast and with so much violence that a power of 120 metric tons of TNT is released into the asteroid. The rock liquifies and the tungsten melts away, carving a wound that tunnels through the asteroid.
The mass of the penetrator is 2.5 tons and the relative speed between the penetrator and the asteroid is 20 km/s. This means that the penetrator impacts the asteroid with an energy of:
E = mv2/2 = (2.5 × 103 kg) × (20,000 m/s)2 /2 = 5 × 1011 J = 120 ton of TNT
We thank our expert Sasha Cohen for the following comment:
Quote: “Liquification of the asteroid material is only one component of the process. At these speeds, most of the material in the immediate vicinity of the impact is vaporized or ionized and forms an extremely high temperature vapor/gas/plasma mixture. The pressure of this mixture contained within the impact cavity is what drives the complete disruption of the asteroid.”
—The damage is too much, and with all of this energy looking for a place to go, the asteroid is blasted into thousands of pieces.
Simulation for the case of 2.5 ton penetrator, 100m asteroid. Effects on the asteroid. Provided by Philip Lubin, Sasha Cohen and Brin Bailey. (2025)
—The debris spreads out into a diffuse cloud. A day later the fragments hit earth, dispersed over hundreds of thousands of square kilometers and creating a beautiful night sky full of shooting stars instead of deadly explosions.
Simulation for the case of 2.5 ton penetrator, 100m asteroid. Effects of asteroid fragments on Earth. Provided by Philip Lubin, Sasha Cohen and Brin Bailey. (2025)
—Planet killers are objects so vast and powerful that they would end most life on earth in a single strike.
In this section, we are considering a collision with a 5 km comet.
#Encyclopedia Britannica: “Planetary defense” (retrieved 2025)
https://www.britannica.com/science/planetary-defense
Quote: “That Earth impacts could pose a danger to humanity was made more evident with the proposal in 1980 that an asteroid impact had likely caused the extinction of 80 percent of Earth’s animal life, including the dinosaurs, 66 million years ago.In 1990 Congress asked the National Aeronautics and Space Administration (NASA) to study how to discover more asteroids that would cross Earth’s orbit (and thus would be likely to collide with Earth) and how to alter the orbits of or to destroy such dangerous asteroids. It was determined that the most dangerous asteroids were those with a diameter larger than 1 km (0.6 miles), the so-called “planet-killer” asteroids.”
—.The most dangerous ones are comets from the outer fringes of the solar system, so distant and dark that tracking them is impossible. Comets are dirty ice balls the size of mountains, more fragile than pure rock but also much faster and violent, traveling at around 140,000 km per hour.
#NASA: “Comets” (retrieved 2025)
https://science.nasa.gov/solar-system/comets/
#Atkinson, Harry (2001): “Risks to the Earth from impacts of asteroids and comets”, Europhysics News vol.32, 4, 126-129
https://www.europhysicsnews.org/articles/epn/abs/2001/04/epn01403/epn01403.html
Quote: “The near Earth comets, essentially "dirty snowballs", are in highly elliptical orbits with long periods ranging from scores of years (for example Halley's comet at 75 years) to periods so long that they are essentially "one-offs", like Hale-Bopp. These long period comets are totally unpredictable, and can be seen approaching no more than a year before possible collision, making them particularly dangerous. Fortunately, long.period comets are only a fraction of all comets; and comets in general are less numerous than asteroids: but comets travel faster and therefore have much more energy.”
While we have come a long way in tracking near-earth objects like asteroids and comets, comets are still relatively difficult to surveil, while remaining faster and more massive.
#Nuth, Joseph A.; Barbee, Brent; Leung, Roland (2018): “Defending the Earth from Long-period comets and Sneaky Asteroids: Short Term Threat Response Requires Long Term Preparation”, The journal of space safety engineering, vol. 5,3-4, 197-202.
https://pmc.ncbi.nlm.nih.gov/articles/PMC6999729/
Quote: “While asteroidal impacts are of order 100 times more likely than cometary impacts, comet impacts can carry more than 100 times the energy of a typical asteroid threat, making their destructive power nearly equal. Cometary threats have been largely ignored to date, a situation that needs to change as our Planetary Defense efforts become more mature. [...]
The average comet is much larger than the typical asteroid by a factor of at least three or more [2]. Since the mass of an object scales as the cube of the diameter (for constant density) the average comet could easily be a factor of ten times more massive than a typical asteroid even though its average density could be as little as 0.6 g/cc. The second important factor in the destruction potential of an impact is velocity. Typical asteroid impacts will have velocities on the order of 20 km/s. Comet impacts could potentially occur over a much wider – and generally higher - range in velocity.
Meteor streams are the result of the earth passing through the debris clouds shed by comets along their orbits through the inner solar system [3]. In essence, these streams represent comets that might have impacted the earth had it been in a different spot along its orbit. If we take the velocities of meteors in meteor streams as proxies for the potential collision velocities of these comets we find that they range from a low near 3 km/s to a high of 71 km/s (see Table 1), with the median at 39.5 km/s and the mean at 41.5 km/s. Therefore the typical comet will impact at about twice the velocity of a typical asteroid.”
We consider a comet travelling at a speed of 40 km/s or 140,000 km per hour with respect to Earth.
—In 2020 the comet NEOWISE, with power of 6,000 times of all the nuclear bombs on Earth, was discovered just 4 months before its closest approach to Earth.
Comet C/2020 F3 NEOWISE was discovered four months before its closest approach. It was 5 km in diameter and travelled at 64 km/s with respect to Earth.
#Khalil, Mohammed et al. (2020): “The Dazzling Comet C/2020 F3 (NEOWISE): The Comet of The Century”, International Journal of Advanced Astronomy, vol. 8, 2
Quote: “The nucleus of NEOWISE comet is about 5 km wide and it is travelling with a speed of 231,000 km/h (64 km/s).”
#Faggi, Sara et al. (2021): “The Extraordinary Passage of Comet C/2020 F3 NEOWISE: Evidence for Heterogeneous Chemical Inventory in Its Nucleus”, The Astronomical Journal, vol. 162, 5
https://iopscience.iop.org/article/10.3847/1538-3881/ac179c
Quote: “The comet’s closest approach to Earth was on 2020 July 23 (Δ = 0.692 and Rh = 0.630 au)”
#Biver, Nicolas et al. (2022): “Observations of comet C/2020 F3 (NEOWISE) with IRAM telescopes”, Astronomy & Astrophysics, vol. 668, A171
https://www.aanda.org/articles/aa/full_html/2022/12/aa44970-22/aa44970-22.html
Quote: “Comet C/2020 F3 (NEOWISE) is a long-period (incoming P ~ 4550 yr) Oort cloud comet on a retrograde orbit (inclination = 128o)1, which came close to the Sun (perihelion at 0.29 au) on 3.7 July 2020 UT. It was discovered on 27.8 March 2020 by the Near-Earth Object Wide-field Infrared Survey Explorer (NEOWISE) at rh = 2.1 au from the Sun (Masiero 2020).”
If the composition and structure of NEOWISE is typical, its bulk density is of around 0.6 g/cm3.
#Britt, Daniel T.; Consolmagno, Guy J.; Merline, William J. (2006): “Small Body Density and Porosity: New Data, New Insights”, 37th Annual Lunar and Planetary Science Conference, 2214
https://web.archive.org/web/20081217064607/http://www.lpi.usra.edu/meetings/lpsc2006/pdf/2214.pdf
Then, its mass is:
m = (4𝜋 (D/2)3/3) × ⍴ = (4𝜋 (5,000 m /2)3/3) × 600 kg/m3 = 3.9 × 1013 kg
And its kinetic energy:
E = mv2/2 = (3.9 × 1013 kg) × (64,000 m/s)2 /2 = 8.0 × 1022 J = 1.9 × 1013 ton of TNT
A typical US warhead has the power of 200,000 tons of TNT. There is about 15,000 warheads in the world, so, in total, the power of all nuclear bombs on Earth is:
15,000 bombs × 200,000 ton of TNT/bomb = 3 × 109 ton of TNT
#Bulletin of the Atomic Scientists: “United States nuclear forces, 2018” (retrieved 2025) https://www.tandfonline.com/doi/pdf/10.1080/00963402.2018.1438219?needAccess=true
And finally:
1.9 × 1013 ton of TNT / 3 × 109 ton of TNT ~ 6,000
—First of all our planet killer comet has SO much more mass than a tiny killer asteroid that, simply breaking it into millions of pieces would not help us that much. The chunks that would hit earth would still be massive and numerous enough to set the sky ablaze and kill most life on earth.
#Lubin, Philip; Cohen, Alexander “Sasha” N. (2025): “Don’t Forget to Look Up” (Preprint)
https://arxiv.org/pdf/2201.10663
Quote: “As discussed extensively in our PI paper, bolide threats below about 1 km can be mitigated solely “within the Earth’s atmosphere,” while larger threats have too much energy to be safely absorbed. However, when it comes to truly existential threats with diameters greater than about 5 km, the amount of energy released in the acoustic and optical signatures and even the dust production becomes so large as to overwhelm our atmospheric protective shield. For large diameter existential threats, it is necessary to have the great majority of the threat miss the Earth completely. This is discussed in detail in our PI paper.“
—So we need to make most if not all of its fragments to completely miss earth – but to do that we need to destroy it MUCH farther away – as far away as Mars.
The point and timing of intercept have been confirmed in private communications with experts Philip Lubin, Sasha Cohen and Brin Bailey.
— And to destroy a mountain, we need way more penetrators – hundreds of thousands.
We thank our expert Philipp Lubin for the following comment:
“If you want to think of the case of using 300 MT of total energy against a massive comet, the answer would be (approximately) that you 8000x more mass if you use purely passive penetrators in this case (40 km/s). For the 300 MT case against a comet (for example) and assuming a nuclear yield of 2 KT/kg (modern thermonuclear) then you need 300 MT/ (2MT/T) = 150 Tons of mass to be launched. [...] To deliver the equivalent energy with passive penetrators for the 40 km/s case would require 8000x larger mass which is not feasible.”
So we would have to launch:
150 tons × 8,000 / 2.5 ton per penetrator = 480,000 penetrators
—And this is well, a huge problem. To travel this far and to transport this much payload, we need at least 24,000 super heavy rockets. As of today, humanity has… two, and not really finished yet. Even if all the industries in the world do nothing but switch to building rockets, we would not finish in time. If we actually discovered a planet killer today, there is literally nothing we could do about it.
The two super-heavy rockets we mean here are SpaceX Starship and NASA's SLS.
However, an even heavier lift vehicle than even NASA’s most advanced SLS could be necessary for this mission. We thank expert Philip Lubin for the following comment:
Quote: “To take 300 MT of nuclear explosive you need a conservation mass of 150 tons (2 MT/ton). [...] Another path is to use higher yield to mass thermonuclear weapons. The most advanced US thermonuclear weapons (not currently in the arenal) were 5 MT/ton which would give 300 MT/ (5MT/ton) = 60 tons of nuclear weapons. However you still need the passive penetrators (4x 10 ton = 40 ton). This would give a total mass needed for the advanced case of nuclear weapons of 5MT/ton for 300 MT giving 60 tons of mass as above + 40 tons (4x 10 ton penetrator) = 100 ton of mass needed.
This would be inconsistent with the most advanced SLS proposed (Block 2B) but could be consistent with the Space X Starship or other future heavy lift vehicles.”
We thank our expert Sasha Cohen for the following comments:
Quote: “Examples of super heavy lift vehicles [like the ones required to use this method against a planet killer] would be the SpaceX Starship and NASA's SLS. There has been exactly one SLS launch since its conception in 2011, and only 8 test flights (with ~50% success rate) of the SpaceX Starship since its conception in 2012. This suggests that it is not the burden on manufacturing capacity which is the limiting factor, but rather the demonstrability of an operational launch vehicle (at least in the case of SpaceX). Turns out rocket science is really hard! 🚀”
Assuming that we could mass produce super heavy rockets that can carry around 50 ton of cargo (approximately like SLS, though less than Space X Starship) , we would need a total of 24,000 of them:
480,000 penetrators × 2.5 ton / 50 ton per rocket = 24,000 rockets
—As soon as the planet killer is spotted on its way to wipe us out we launch a single rocket to meet it. For 5 long months it travels through the nothingness of space as life on Earth nervously continues. Finally it reaches its destination a bit beyond the orbit of Mars.
The point and timing of intercept have been confirmed in private communications with experts Philip Lubin, Sasha Cohen and Brin Bailey.
—Now we deploy 5 massive penetrators in sequence, one perfectly lined up two kilometers after the other.
We thank our expert Sasha Cohen for the following comments:
Quote: “We have not yet run simulations of sequential penetrators at the scale of a multi-kilometer size target, so it is unclear as to the specific requirements that will be necessary. In general, we see that an acceptable fraction of the yield of an NED will be coupled into the target even if the depth of burst is only a few tens of meters below the surface, though deeper is always better. So that being said, 5 sequential penetrators of multi-metric ton mass should be sufficient for delivering an NED below the surface. [...]
The spacing will be determined by a number of complex things, including what it is like inside the wake produced by the first penetrators and how well we are able to keep the penetrators in line with each other. The optimal spacing is currently not a known parameter, but as an educated guess I would space each penetrator 1-2 km behind the other (so 5-10 km total spacing).”
While the first four penetrators are around 10 tons, the last penetrator will need to also carry the weight of its explosive charge. For more details on how much mass that could be assuming we are using our typical current thermonuclear weapons see the comment from the expert Philip Lubin below, as well as for the details of a more realistic scenario.
—The engineering challenge of aligning and timing this correctly is horrendous and we only have one attempt. So a few very brave astronauts went on this one way trip to supervise the process, with no way home.
We have chosen this scenario for dramatic effect and because it would save the time necessary to manufacture and test the machines necessary to automate this mission, but it is important to note that the mission could be automated or controlled remotely.
We thank our expert Sasha Cohen for the following comment:
Quote: “Please note that we do NOT envision astronauts taking any part in this process. All maneuvers and operations would be performed robotically, remotely, or autonomously.”
— The comet smashes into the first penetrator at 140,000 km/h, unleashing the power of 2,000 tons of TNT
In the reference system of the comet, a penetrator is coming at it with a speed of 140,000 km/h or 40 km/s. The energy of the impact is:
E = mv2/2 = (103 kg) × (40,000 m/s)2 /2 = 8 × 1012 J = 2,000 ton of TNT
—Ice, rock and tungsten liquify in an instant. the energy of the impact eats itself dozens of meter deep into the mountain
We thank our expert Sasha Cohen for the following comments:
Quote: “On the timescale of the multiple penetrators impacting, there will be no time for the impact site to evolve in a crater before the next penetrator hits. Rather, it's more like a deep narrow channel perhaps 5-10 meters in diameter and a few dozen meters deep when the next penetrator arrives.”
—Here is the second one, perfectly hitting the same spot punching directly into the crater, smashing, melting, drilling. The third and fourth penetrators repeat the process again, now smashing a tunnel about 100 meters deep.
We thank our expert Sasha Cohen for the following comment:
Quote: “[T]here will be no time for the impact site to evolve in a crater before the next penetrator hits. Rather, it's more like a deep narrow channel perhaps 5-10 meters in diameter and a few dozen meters deep when the next penetrator arrives. [...] In general, penetrators of the same mass as the previous one will penetrate the same depth as the first (so an additional few dozen meters [each])”
The “crater” we mention here is not a crater in the habitual sense, but rather the tube-like hole shown on screen.
—And then comes the final penetrator and its toxic load. A 300 megatons in nuclear warheads – 20,000 times more energy than the bomb that destroyed Hiroshima. It travels deep into the tunnel and just before it hits the end, it explodes.
We thank our expert Philip Lubin for the following comment:
Quote: “For the 300 MT case against a comet (for example) and assuming a nuclear yield of 2 KT/kg (modern thermonuclear) then you need 300 MT/ (2MT/T) = 150 Tons of mass to be launched. Please keep in mind that we WOULD NOT launch a single 300 MT weapons as none exist so we would launch a large number of small weapons (say ~ 1 MT) along with passive penetrators to "drill” the holes where the nuclear weapon enters and detonates.”
Sasha Cohen adds:
Quote: “The series of penetrators is spaced apart from each other such that the wake left behind by the leading penetrators is allowed to disperse over an acceptably long time period (typically 1 second to a few seconds). This ensures that the final penetrator carrying the NED only travels through extremely low density material, and can detonate the NED before it reaches the end of the tunnel excavated by the leading penetrators. In this way, the NED is isolated from extreme g-loading prior to detonation.”
This prevents the nuclear bomb from being destroyed previous to its detonation.
The explosive charge ot 300 MT is equivalent to 20,000 times the Hiroshima bomb:
3 × 108 ton of TNT / 15, 000 ton of TNT = 20,000
#USDE: The Manhattan Project, an Interactive Story: The Atomic Bombing of Hiroshima” (retrieved 2025)
https://www.osti.gov/opennet/manhattan-project-history/Events/1945/hiroshima.htm
Google Sites
Report abuse