Asteroid Impact Energy Calculator
Calculate the kinetic energy released when an asteroid strikes Earth, expressed in megatons of TNT. Use it to compare historical impacts or assess the potential effect of a hypothetical impactor.
About this calculator
The kinetic energy of an impacting asteroid is E = ½mv², where m is the asteroid's mass and v is its velocity relative to Earth. Mass is derived from the asteroid's volume (assuming a sphere) and density: m = (4/3)π(d/2)³ × ρ. The full formula expressed in this calculator is: E (megatons) = 0.5 × (4/3 × π × (diameter/2)³) × density × (velocity × 1000)² × sin(angle × π/180) / 4.184×10¹⁵. Velocity is converted from km/s to m/s by multiplying by 1000. The sine of the impact angle accounts for the fact that a grazing impact delivers less energy to the surface than a vertical strike. Division by 4.184×10¹⁵ converts joules into megatons of TNT (1 megaton = 4.184×10¹⁵ J).
How to use
Consider a stony asteroid 50 m in diameter hitting at 20 km/s at a 45° angle with density 2500 kg/m³ (typical stony composition). Step 1 — volume: (4/3)π(25)³ = 65,450 m³. Step 2 — mass: 65,450 × 2500 = 163,600,000 kg. Step 3 — velocity in m/s: 20 × 1000 = 20,000 m/s. Step 4 — sin(45°) ≈ 0.707. Step 5 — energy: 0.5 × 163,600,000 × (20,000)² × 0.707 / 4.184×10¹⁵ = 0.5 × 163,600,000 × 400,000,000 × 0.707 / 4.184×10¹⁵ ≈ 5.5 megatons. This is comparable to the 1908 Tunguska event, estimated at 10–15 megatons.
Frequently asked questions
How does asteroid size affect the impact energy compared to velocity?
Kinetic energy scales with the cube of diameter (through volume and hence mass) but with the square of velocity. This means doubling the diameter increases energy by a factor of 8, while doubling the velocity increases it by only a factor of 4. For this reason, large asteroids are disproportionately more dangerous than fast ones: a 1 km asteroid releases roughly 100,000 times more energy than a 100 m asteroid traveling at the same speed. Size is the dominant factor in assessing catastrophic risk from near-Earth objects.
Why does the impact angle affect how much damage an asteroid causes?
A vertical (90°) impact delivers the maximum energy directly into the ground, excavating the deepest and widest crater and coupling the most energy into seismic waves and ejecta. At shallower angles, more of the trajectory is spent traveling through the upper atmosphere, where the asteroid decelerates and sheds energy as an airburst rather than a ground impact. The sin(angle) factor in the formula approximates this effect — a 30° impact delivers sin(30°) = 0.5 times the ground energy of a vertical strike. Very shallow impacts (below ~20°) are more likely to produce airbursts or even skip off the atmosphere entirely.
What units does the calculator use and why are megatons of TNT used for asteroid energy?
The calculator outputs energy in megatons of TNT equivalent (Mt TNT), where 1 megaton equals 4.184×10¹⁵ joules of energy. This unit is used because it provides an immediately intuitive frame of reference — nuclear weapons are rated in megatons, and most people have some sense of their scale. The largest nuclear weapon ever detonated (Tsar Bomba) released about 50 Mt; the Chicxulub impactor that ended the dinosaurs released roughly 100 million Mt. Using joules or kilowatt-hours would produce unwieldy numbers that are harder to contextualize for impact hazard communication.