Asteroid Impact
Pick a size, material, speed and angle — and feel the energy in joules and megatons of TNT.
Pick a size, a material, a speed and an angle. The atmosphere gets the first say — small, weak bodies burst in the sky, big or strong ones punch through — then the energy becomes a fireball, a blast wave and a crater. Every number comes from the published equations of the Earth Impact Effects Program.
Small numbers: density in kg/m³.
11 km/s is the slowest possible (Earth's escape speed); 72 km/s is a head-on retrograde comet.
Measured from the horizon: 90° is straight down. 45° is the most likely angle.
Damage rings at true scale
Tap or drag on the map — or use the slider — to read the effects at any distance.
- Crater 2.4 km
- Fireball 3.5 km
- Clothing ignites 28 km
- Third-degree burns 42 km
- Second-degree burns 54 km
- 20 psi · concrete buildings destroyed 24 km
- 5 psi · most houses collapse 48 km
- 1 psi · windows shatter 130 km
At 53 km from ground zero
- The heat causes second-degree burns
- The blast shatters windows
- Peak overpressure
- 28 kPa
- Peak wind
- 60 m/s
- Heat (thermal radiation)
- 860 kJ/m²
- Ejecta layer
- 1.6 cm
Crater cross-section (true scale 1:1)
A complex crater's floor rebounds: flat floor, terraced walls, central peak (shape schematic; diameter and depth from the model). At true scale, big craters are astonishingly shallow.
Size to scale
Effects vs distance
| Distance | Peak overpressure | Peak wind | Heat (thermal radiation) | Ejecta layer | What happens |
|---|---|---|---|---|---|
| 5 km | 4.1 MPa | 1,600 m/s | 110 MJ/m² | 19 m | The heat sets clothing on fire The blast destroys reinforced-concrete buildings |
| 10 km | 870 kPa | 700 m/s | 26 MJ/m² | 2.4 m | The heat sets clothing on fire The blast destroys reinforced-concrete buildings |
| 20 km | 190 kPa | 280 m/s | 6.5 MJ/m² | 30 cm | The heat sets clothing on fire The blast destroys reinforced-concrete buildings |
| 50 km | 32 kPa | 66 m/s | 980 kJ/m² | 1.9 cm | The heat causes second-degree burns The blast shatters windows |
| 100 km | 10 kPa | 22 m/s | 190 kJ/m² | 2.4 mm | The blast shatters windows |
Blast: Collins et al. (2005) fit to 1 kt test data (Glasstone & Dolan 1977), scaled with the cube root of the energy. Heat: 0.3 % of the energy becomes radiation; burn and ignition thresholds grow as E^(1/6). Ejecta: thickness of the layer that lands at that distance.
How the model works
The asteroid's kinetic energy is E = (π/12) ρ L³ v², with density ρ, diameter L and speed v. One megaton of TNT is 4.184 × 10¹⁵ joules.
On the way down, the air pushes on the front of the body with a pressure of about ρ_air v². Once that exceeds the body's strength, it breaks up; the fragment cloud flattens like a pancake, and if it spreads to seven times its original width before reaching the ground, all the energy is released at once as an airburst. That is how Chelyabinsk and Tunguska exploded without leaving craters.
If it reaches the ground, π-scaling gives the transient crater dug in the first seconds. Its walls slump into a final bowl 25 % wider (a simple crater) or — above about 3.2 km — collapse into a wide, shallow complex crater with a central peak.
Above about 15 km/s the impact vaporises rock into a fireball whose heat burns at a distance. The blast wave follows, and the ground shakes with magnitude M = 0.67 log₁₀E − 5.87 (E in joules).
The equations used
-
E = (π/12) ρᵢ L³ v²Collins et al. 2005, eq. 1 -
Yᵢ = 10^(2.107 + 0.0624 √ρᵢ)Collins et al. 2005, § entry -
z_b = z* − 2H ln[1 + (l/2H) √(f_p² − 1)], f_p = 7Collins et al. 2005, eq. 18 -
D_tc = 1.161 (ρᵢ/ρ_t)^⅓ L^0.78 vᵢ^0.44 g^−0.22 sin^⅓θCollins et al. 2005, eq. 21 -
D_fr = 1.25 D_tc | D_fr = 1.17 D_tc^1.13 / D_c^0.13Collins et al. 2005, eq. 22, 27 -
R_f = 0.002 E^⅓, φ = f η E / (2π r²), η = 3×10⁻³Collins et al. 2005, § thermal -
p = (p_x r_x / 4r₁)(1 + 3 (r_x/r₁)^1.3), r₁ = r / E_kt^⅓Collins et al. 2005, § air blast -
M = 0.67 log₁₀E − 5.87Collins et al. 2005, § seismic -
t_e = D_tc⁴ / (112 r³)Collins et al. 2005, § ejecta
Real impacts: model vs record
Each preset feeds the event's best-estimate size, material, speed and angle into the model. The record column is what was actually observed or reconstructed — compare them to see how far a simple model gets.
| Event | Inputs | Model | Record | Source |
|---|---|---|---|---|
| Chelyabinsk 2013 | 19 m · Dense rock · 19 km/s · 18° | 465 kt TNT airburst at 33 km | 440–500 kt TNT airburst at ≈ 30 km | Brown et al. 2013, Nature 503, 238; Popova et al. 2013, Science 342, 1069 |
| Tunguska 1908 | 60 m · Dense rock · 16 km/s · 35° | 10.4 Mt TNT airburst at 7.8 km | 3–15 Mt TNT airburst at 5–10 km | Boslough & Crawford 2008, Int. J. Impact Eng. 35, 1441 |
| Meteor Crater ≈ 50 ka | 40 m · Iron · 18 km/s · 45° | 10.4 Mt TNT crater 1.2 km | crater ≈ 1.2 km | Melosh & Collins 2005, Nature 434, 157 |
| Chicxulub 66 Ma | 12 km · Dense rock · 20 km/s · 60° | 1.3×10⁸ Mt TNT crater 150 km | crater ≈ 180 km | Hildebrand et al. 1991, Geology 19, 867; Collins et al. 2020, Nat. Commun. 11, 1480 |
How sure are these numbers?
- The size, density, speed and angle of a real impactor are rarely known to better than tens of percent — and the energy grows with the cube of the size and the square of the speed.
- The crater, blast and heat formulas are fits to experiments, nuclear-test data and simulations: good to within a factor of a few, not to the last digit. Our Chicxulub preset, for example, gives a crater of about 150 km against the roughly 180 km observed.
- The pancake model of break-up is deliberately simple; newer fragmentation models give somewhat different burst heights. The heat of airbursts and tsunamis are not modelled. Damage thresholds such as “5 psi collapses most houses” come from nuclear-weapon tests and depend on how buildings are built.
- Very small or slow bodies are braked to a few km/s or less and make small pits; the crater equation (gravity regime) overestimates them.
Questions
How much energy did the asteroid that killed the dinosaurs release?
Roughly 10²³–10²⁴ joules — on the order of 100 million megatons of TNT, billions of Hiroshima bombs. A body about 10–15 km across struck Chicxulub, Mexico, 66 million years ago at around 20 km/s and left a crater about 180 km wide.
Why didn't Chelyabinsk or Tunguska leave a crater?
Both were stony bodies tens of metres across. Air pressure crushed them high in the atmosphere — about 30 km up for Chelyabinsk, about 5–10 km for Tunguska — so their energy was released as an airburst. The Tunguska blast flattened about 2,000 km² of Siberian forest.
How often do impacts like these happen?
Collins et al. (2005) give the average interval as about 109 × E^0.78 years, with E in megatons: about every 60 years for a Chelyabinsk-size airburst (0.5 Mt), every 600–700 years for 10 Mt, and on the order of every 100 million years for a Chicxulub-size impact.
What does “5 psi” mean?
Overpressure is how far the blast wave pushes the air pressure above normal (101 kPa ≈ 14.7 psi). 1 psi (6.9 kPa) shatters windows, 5 psi (34 kPa) collapses most houses and 20 psi (138 kPa) destroys reinforced-concrete buildings. These thresholds come from nuclear-test damage surveys (Glasstone & Dolan 1977).
Sources
- Collins, G. S., Melosh, H. J. & Marcus, R. A. (2005). Earth Impact Effects Program. Meteoritics & Planetary Science 40, 817–840.
- Earth Impact Effects Program (Imperial College London / Purdue University)
- Glasstone, S. & Dolan, P. J. (1977). The Effects of Nuclear Weapons, 3rd ed. U.S. DoD/DoE.
- Rumpf, C. M., Lewis, H. G. & Atkinson, P. M. (2017). Population vulnerability models for asteroid impact risk assessment. Meteoritics & Planetary Science 52, 1082–1102.
- Brown, P. G. et al. (2013). A 500-kiloton airburst over Chelyabinsk… Nature 503, 238–241.
- Popova, O. P. et al. (2013). Chelyabinsk airburst, damage assessment, meteorite recovery, and characterization. Science 342, 1069–1073.
- Boslough, M. B. E. & Crawford, D. A. (2008). Low-altitude airbursts and the impact threat. Int. J. Impact Engineering 35, 1441–1448.
- Melosh, H. J. & Collins, G. S. (2005). Meteor Crater formed by low-velocity impact. Nature 434, 157.
- Hildebrand, A. R. et al. (1991). Chicxulub Crater… Geology 19, 867–871.
- Collins, G. S. et al. (2020). A steeply-inclined trajectory for the Chicxulub impact. Nature Communications 11, 1480.
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