Asteroid Impact Calculator
Estimate the energy of an asteroid or meteorite impact in megatons of TNT and Hiroshima bombs, and the size of the crater it would leave, from its diameter, density, speed and entry angle.
How it works
m = ρ π L³ ÷ 6 · E = ½ m v² · 1 Mt TNT = 4.184 × 10¹⁵ J · transient crater D_tc = 1.161 (ρᵢ/ρₜ)^(1/3) L^0.78 v^0.44 g^(−0.22) sin^(1/3)θ (SI units) · final crater: simple D = 1.25 D_tc; complex (D > 3.2 km) D = 1.17 D_tc^1.13 ÷ 3.2^0.13 (km)
The kinetic energy of an impactor grows with the cube of its size and the square of its speed, which is why even small asteroids release nuclear-scale energy. The crater sizes use the scaling laws in the Earth Impact Effects Program of Collins, Melosh and Marcus (2005): the transient crater forms in seconds, then its walls collapse into a final crater about 25% wider, or into a broad complex crater with a central peak once it exceeds about 3.2 km. The model ignores slowing and breakup in the atmosphere, which matters a lot for stony bodies under about 50–100 m — Chelyabinsk (about 18 m) and Tunguska (about 50 m) exploded in the air.
Worked example
A 50 m stony asteroid (3,000 kg/m³) has a mass of 1.96 × 10⁸ kg. Hitting at 20 km/s it carries E = ½ × 1.96 × 10⁸ × 20,000² = 3.93 × 10¹⁶ J = 9.39 Mt TNT, about 626 Hiroshima bombs. At 45° into sedimentary rock the transient crater is about 1.1 km and the final simple crater about 1.37 km across.
Sources: Collins, Melosh & Marcus (2005) Earth Impact Effects Program, Meteoritics & Planetary Science 40, 817–840 · NASA CNEOS — Near-Earth object frequently asked questions
Frequently asked questions
How much energy does an asteroid impact release?
Half its mass times its speed squared. A 50 m stony asteroid at 20 km/s releases about 9 megatons of TNT; a 1 km one about 75,000 megatons; the 10 km Chicxulub impactor around 100 million megatons.
How big a crater does an asteroid make?
Typically 10–20 times the asteroid’s diameter for the final crater. Meteor Crater in Arizona (1.2 km) was made by an iron meteorite roughly 50 m across.
Why does the entry angle matter?
Shallow impacts put less of their momentum into the ground, so they make smaller craters. The crater size scales with sin^(1/3) of the angle; 45° is the most probable angle.
How often do such impacts happen?
Objects of about 50 m hit Earth roughly once every 1,000 years on average, 1 km objects every few hundred thousand years, and 10 km objects about every 100 million years.
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This calculator is for educational purposes. Double-check important results before acting on them.