How to use it
Pick one of the famous impacts, or set your own:
- Diameter, from a 1 m boulder to a 100 km giant.
- What it is made of: comet ice, rock or iron, or any density from 500 to 8,000 kg/m³.
- Speed, from 11 to 72 km/s.
- Angle to the ground.
- Target: sedimentary rock, crystalline rock or water.
Every change recalculates at once. How far the damage reaches shows how far each effect extends, on a scale where each step is ten times farther. Effects at reads the heat, earthquake, ejecta and blast at the distance you choose, marked as a blue line on the chart.
What happens in an impact
Through the atmosphere. The air slows an incoming object, and the pressure on its front rises as the air thickens. When that pressure exceeds the rock's strength, the object breaks apart. The fragments spread sideways, and the rising drag can release most of the energy in an airburst before anything reaches the ground. Objects larger than 1 km cross the atmosphere almost unchanged.
Energy and how often. The energy is half the mass times the speed squared, given in megatons of TNT. The simulator also gives the average time between impacts of that energy anywhere on Earth, from counts of near-Earth asteroids.
The crater. The impact first opens a bowl-shaped transient crater, which then collapses. Below about 3.2 km across, Earth's craters stay simple bowls; larger ones collapse into complex craters, much wider than they are deep. Some of the rock melts.
Heat. Above about 15 km/s the impact vaporizes rock, and the expanding hot plume, the fireball, radiates like a second sun. Its heat can burn skin and ignite clothing, grass and trees, unless the fireball is below the horizon.
Earthquake. About one ten-thousandth of the energy shakes the ground. The simulator gives a Richter magnitude and the Mercalli intensity, the strength of shaking people feel, at your distance.
Ejecta. Rock thrown out of the crater falls back around it. Its thickness drops with the cube of the distance; for smaller impacts the air stops it near the fireball.
Air blast. A shock wave in the air arrives at the speed of sound, followed by violent winds. Its peak pressure is matched to damage observed after nuclear tests: windows shatter, wood frame buildings collapse, trees fall.
Famous impacts
The presets are the examples that the model's authors used to illustrate it:
| Preset | Input | What the model gives |
|---|---|---|
| Tunguska, 1908 | 75 m stony object, 2,000 kg/m³, 17 km/s | Breaks up about 66 km up and explodes about 5 km up; 90% of trees blown down to about 15 km |
| Meteor Crater | 40 m iron asteroid, 20 km/s, sedimentary rock | Slowed by half in the air; a crater about 1.2 km across |
| Ries crater | 1.75 km stony asteroid, 20 km/s, crystalline rock | A complex crater about 24 km across; heat that ignites most combustibles 200 km away |
| Chicxulub | 18 km stony asteroid, 20 km/s, crystalline rock | A crater about 186 km across; a fireball 236 km in radius |
Limits
The simulator gives quick estimates, not a forecast:
- Not covered: tsunamis, dust, wildfires and climate change around the world.
- Air blast: it comes from nuclear test data on a flat Earth with uniform air, so it is least reliable for the largest impacts. Above about 10,000 megatons it probably overstates the blast two to five times.
- High airbursts: the blast is understated. The Chelyabinsk meteor of 2013 was about 18 m across, travelled at 18.6 km/s and released about 440 kilotons, according to NASA. This model puts its burst near 31 km and predicts no damage on the ground. Yet about 44% of Chelyabinsk's apartment buildings had broken glass.
Sources
The model: G. S. Collins, H. J. Melosh and R. A. Marcus (2005), "Earth Impact Effects Program", Meteoritics & Planetary Science 40, 817–840, which draws its damage data from Glasstone and Dolan (1977). Chelyabinsk: NASA CNEOS (March 1, 2013) and Popova et al. (2013), Science 342, 1069. Read October 6, 2026.
Questions
How accurate is this asteroid impact simulator?
It uses the equations of the Earth Impact Effects Program (Collins, Melosh and Marcus, 2005), and our tests reproduce the paper's worked examples. The paper calls its results estimates: the crater-scaling constant could lie anywhere from 0.8 to 1.5, and the air blast comes from nuclear test data.
What size asteroid would destroy a city?
Try it: a 100 m rocky asteroid at 20 km/s carries about 70 megatons, and the simulator shows how far wood frame buildings collapse around it. Smaller stony objects often explode in the air, like the Tunguska example, flattening forest without a crater.
Why do small asteroids explode before they hit the ground?
Air pressure on the front of a fast object grows as it descends until it exceeds the rock's strength. The object then breaks up, the fragments spread sideways, and the drag rises so fast that most of the energy is released in the air.
Does it show tsunamis or climate effects?
No. The model behind it does not estimate tsunamis or global effects such as dust and wildfires, because both need far more detail than a quick model can hold.