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This JavaScript program (by Stephen R. Schmitt) calculates the effects of the impact of an object hitting the earth. It was adapted from a BASIC program from the Astronomical Computing column of Sky & Telescope, November 1996.

To operate the calculator, enter desired values to describe an impactor and press the Calculate button. You may change any input value and recalculate.

To clear the input windows, press the Clear button.

diameter meters
density grams/cubic centimeter
velocity kilometers/second
graze angle degrees from horizontal


Impactor Parameters

volume cubic meters
kinetic energy joules
mass kilograms
equivalent yield kilotons of TNT

Crater Parameters

actual diameter meters
actual depth meters
volume cubic meters
apparent diameter meters
apparent depth meters
ejecta spread meters


When an asteroid or comet impacts the Earth, the energy released mainly depends on the mass and velocity of the impactor.

Mass is determined by the volume and density of the object. Below is a table of some information known about several of the largest asteroids.

Asteroid name Density - g/cc Diameter - km
1 Ceres 2.05 ± 0.05 466
2 Pallas 4.2 ± 0.3 261
4 Vesta 4.3 ± 0.3 262.5
16 Psyche 1.8 ± 0.6 132
243 Ida 2.7 ± 0.4* 58 x 23
253 Mathilde 1.3 ± 0.2 28.5 x 25
433 Eros 2.67 ± 0.03 17.5 x 6.5
For comparison, the density of water is 1 g/cc, rock about 2 g/cc, and iron about 7 g/cc.

For velocity of an object at impact, consider that the Earth's escape velocity is 11 km/sec. An object falling toward the Earth from a large distance (well beyond the moon) and starting from rest would be moving at close to this velocity on impact. Also, the Earth is moving at about 30 km/sec in its orbit about the sun; an object moving in the opposite direction might impact at more than twice this velocity. Try investigating the other components of the Earth's velocity through space.

Some current information about actual threats to the Earth can be found here: NASA/JPL Near-Earth Object Program

Copyright © 2004, Stephen R. Schmitt