Example data
Click Load to auto-fill the form with a scenario, then press Calculate.
| Scenario | Diameter | Density | Speed | Angle | Porosity | Surface energy | |
|---|---|---|---|---|---|---|---|
| Small stony (training) | 10 m | 3,000 kg/m³ | 20 km/s | 45° | 0% | 0.075 Mt | |
| City-scale airburst style | 20 m | 3,000 kg/m³ | 19 km/s | 35° | 10% | 0.41 Mt* | |
| Dense iron body | 50 m | 7,800 kg/m³ | 25 km/s | 50° | 2% | 36.6 Mt* | |
| Large stony (regional) | 140 m | 3,000 kg/m³ | 20 km/s | 45° | 0% | 206 Mt | |
| Rubble pile (high porosity) | 200 m | 2.2 g/cm³ | 17 km/s | 60° | 35% | 370 Mt* | |
| Shallow grazing impact | 80 m | 3,200 kg/m³ | 22 km/s | 10° | 5% | 64 Mt* | |
| Fast, small iron fragment | 15 m | 7,500 kg/m³ | 30 km/s | 70° | 0% | 3.03 Mt | |
| Slow, large stony | 300 m | 2,800 kg/m³ | 12 km/s | 45° | 15% | 1,247 Mt* |
* Rows with * assume energy reaching surface < 100% and/or porosity > 0%.
Formula used
- Volume: V = (π/6) · d³ · S where d is diameter and S is the shape factor.
- Effective density: ρ_eff = ρ · (1 − P) where P is porosity fraction.
- Mass: m = ρ_eff · V
- Kinetic energy: E = ½ · m · v²
- Energy reaching surface: E_s = E · F where F is the reaches-surface fraction.
- Normal-component energy: E_n = ½ · m · (v·sinθ)² · F
- TNT equivalent: Mt = E_s / 4.184×10¹⁵
How to use this calculator
- Enter the asteroid diameter and select its unit.
- Set a density that matches your assumed composition.
- Provide impact speed, then choose the speed unit.
- Open advanced options for angle, porosity, and energy losses.
- Click Calculate to view energy and equivalents.
- Use Download CSV or Download PDF for sharing.
Asteroid impact energy guide
1) Why kinetic energy dominates
Impacts are mainly a speed story because kinetic energy scales with v². Doubling speed quadruples energy, even if size stays fixed. Near‑Earth objects typically arrive between about 11 and 30 km/s, while the Solar System’s upper limit at Earth is near 72 km/s. The calculator converts your velocity choice to m/s before applying E = ½mv².
2) Size sets the mass quickly
Diameter is even more dramatic because volume scales with d³. A 100 m body has 1,000× the volume of a 10 m body, assuming similar shape. The model uses a spherical base volume (π/6)d³ and multiplies by the shape factor to represent slightly elongated or flattened rocks.
3) Density and porosity change the outcome
Bulk density varies widely: porous stony objects may sit around 2,000–3,500 kg/m³, while metal‑rich bodies can exceed 7,000 kg/m³. Porosity reduces effective density using ρ_eff = ρ(1 − P). For example, 3,000 kg/m³ at 30% porosity behaves like 2,100 kg/m³, cutting mass and energy by 30%.
4) Converting joules to TNT equivalents
To make results easier to compare, surface‑coupled energy is translated to TNT: one megaton is 4.184×10¹⁵ joules. A 20 m, 3,000 kg/m³ body at 19 km/s is on the order of half a megaton if most energy reaches the surface. The table examples let you load similar scenarios instantly.
5) Angle helps compare “downward” coupling
Total kinetic energy is independent of impact angle, but the normal component uses v·sinθ. Shallow entries can spread effects over a longer path, while steep entries concentrate momentum downward. This calculator reports both total energy and the normal‑component energy to support quick comparisons across angles like 10°, 45°, and 70°.
6) Energy reaching the surface is a practical knob
Fragmentation and airburst behavior can prevent full coupling to the ground. The “energy reaching surface” percentage is a simplified way to explore that uncertainty. Setting 75% means you are treating 25% of the kinetic energy as lost to atmospheric breakup, radiation, or lateral blast before ground coupling.
Finally, the timescale converts energy into an average power estimate. For example, 1 Mt delivered over 1 second implies about 4.184×10¹⁵ watts. Shorter durations raise peak intensity significantly.
FAQs
1) What density should I use for a typical asteroid?
For a stony object, try 2,500–3,500 kg/m³. For an iron‑rich body, try 7,000–8,000 kg/m³. If you expect a rubble pile, combine lower density with 20–50% porosity.
2) Why does the angle not change total energy?
Kinetic energy depends on mass and speed only. Angle changes how velocity splits into horizontal and vertical parts, so the calculator also shows normal‑component energy using v·sinθ.
3) What does “energy reaching the surface” represent?
It is a simple loss factor for breakup and airburst effects. Use 100% for a fully coupled strike, or reduce it (for example 50–90%) to explore cases where not all energy couples to the ground.
4) How accurate are TNT equivalents?
The conversion is exact by definition (1 Mt = 4.184×10¹⁵ J). The uncertainty comes from your inputs: size, density, porosity, speed, and how much energy truly couples to the surface.
5) Why include a shape factor?
Real bodies are rarely perfect spheres. The shape factor multiplies spherical volume to approximate elongated or irregular objects without requiring full 3D geometry. Keeping it near 1.0 is a good default.
6) Can this predict crater diameter or damage radius?
No. It reports energy, momentum, and power scaling. Crater size and damage depend on altitude, fragmentation, entry dynamics, target geology, and water depth. Use specialized models if you need impact effects.