What Is an Impact Crater Diameter Estimator?

An impact crater diameter estimator takes the size, velocity, density and angle of an impactor and the properties of the target body, and works out how large a crater the collision leaves behind. It reports the kinetic energy in TNT equivalent, the transient cavity that opens in the first seconds, the final diameter after the walls collapse, the depth, the ejecta blanket, the equivalent seismic magnitude and the average interval between impacts of that size.

The reason the answer needs a model rather than a rule of thumb is that a hypervelocity impact is not a hole punched in the ground. Almost all of the impactor's energy goes into compressing, melting and throwing the target material, and the crater that remains is the product of an excavation phase followed by a collapse phase whose behaviour depends on the planet's gravity.

How It Works

The energy comes first. The impactor is treated as a sphere, its volume multiplied by the density of the chosen material gives the mass, and half the mass times the square of the velocity gives the kinetic energy — which for a 50 metre stony body arriving at 17 km/s is about 10¹⁶ joules, or roughly a quarter of a megaton of TNT. That single number drives everything else.

Crater size follows from Pi-group scaling, the framework that lets laboratory shots with centimetre projectiles be extrapolated to planetary impacts. In the gravity-dominated regime the transient crater diameter grows with the cube root of the ratio of impactor to target density, with the impactor diameter and velocity raised to fitted exponents, and shrinks weakly with the target's gravity — which is why the Moon keeps a much larger crater from the same impactor than Earth does. The angle of arrival enters as the cube root of its sine, so a 30 degree impact produces about 79 percent of the diameter of a vertical one.

The final crater then depends on the transient size relative to the body's simple-to-complex transition diameter: about 3 to 4 km on Earth, 7 km on Mars and 15 km on the Moon. Below the transition the transient cavity relaxes slightly and keeps a depth-to-diameter ratio near one to five; above it the walls fail, the floor rises and the crater widens while becoming proportionally shallower. The model also converts the energy to an equivalent seismic magnitude using the standard seismic efficiency of 10⁻⁴, estimates the fireball radius from the cube root of the yield, and places the result against Barringer, Ries, Chicxulub and Vredefort so the scale is immediately legible.

Understanding Your Results

The primary card is the final crater diameter on the selected body. The three-stat bar adds the energy yield in megatons, the transient crater diameter and the equivalent seismic magnitude.

The breakdown table carries every step: the impactor volume and mass, the velocity, the kinetic energy and its TNT equivalent, the angle factor, the density-ratio and gravity terms, the transient and final diameters, the depth, the morphology verdict against the body's transition diameter, the ejecta blanket, the fireball, the seismic magnitude, the recurrence interval and the comparison with four real craters. The summary panel repeats the headline figures.

Two cautions belong with the numbers. The scaling relation is calibrated on the gravity-dominated regime, which is the right one for craters above a few hundred metres; small craters form in the strength-dominated regime where target rock strength rather than gravity controls the size, and the exponents there are different. The model also assumes a solid, uniform target and a vertical-to-oblique impact above roughly 15 degrees, below which craters become elliptical and the energy deposition changes character. For comparison and education — how much bigger is Chicxulub than Barringer, and how much energy does that take — it is a sound guide; for a specific real impact structure, the geology on the ground is the arbiter.