Earth Impact Effects Program

Robert Marcus, H. Jay Melosh, and Gareth Collins

Please note: the results below are estimates based on current (limited) understanding of the impact process and come with large uncertainties; they should be used with caution, particularly in the case of peculiar input parameters. All values are given to three significant figures but this does not reflect the precision of the estimate. For more information about the uncertainty associated with our calculations and a full discussion of this program, please refer to this article

Your Inputs:

Distance from Impact: 100.00 km ( = 62.10 miles )
Projectile diameter: 12.00 km ( = 7.45 miles )
Projectile Density: 518 kg/m3
Impact Velocity: 20.00 km per second ( = 12.40 miles per second )
Impact Angle: 90 degrees
Target Density: 2500 kg/m3
Target Type: Sedimentary Rock


Energy before atmospheric entry: 9.37 x 1022 Joules = 2.24 x 107 MegaTons TNT
The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 5.0 x 107years

Major Global Changes:

The Earth is not strongly disturbed by the impact and loses negligible mass.
The impact does not make a noticeable change in the tilt of Earth's axis (< 5 hundreths of a degree).
The impact does not shift the Earth's orbit noticeably.

Crater Dimensions:

What does this mean?

Transient Crater Diameter: 49.3 km ( = 30.6 miles )
Transient Crater Depth: 17.4 km ( = 10.8 miles )

Final Crater Diameter: 82.3 km ( = 51.1 miles )
Final Crater Depth: 1.12 km ( = 0.693 miles )
The crater formed is a complex crater.
The volume of the target melted or vaporized is 831 km3 = 199 miles3
Roughly half the melt remains in the crater, where its average thickness is 435 meters ( = 1430 feet ).

Thermal Radiation:

What does this mean?

Time for maximum radiation: 4.55 seconds after impact

Visible fireball radius: 89.9 km ( = 55.9 miles )
The fireball appears 204 times larger than the sun
Thermal Exposure: 4.41 x 109 Joules/m2
Duration of Irradiation: 19.7 minutes
Radiant flux (relative to the sun): 3740

Effects of Thermal Radiation:

Seismic Effects:

What does this mean?

The major seismic shaking will arrive approximately 20 seconds after impact.
Richter Scale Magnitude: 9.5 (This is greater than any earthquake in recorded history)
Mercalli Scale Intensity at a distance of 100 km:


What does this mean?

The ejecta will arrive approximately 2.4 minutes after the impact.
Your position is beneath the continuous ejecta deposit.
Average Ejecta Thickness: 52.7 meters ( = 173 feet )
Mean Fragment Diameter: 55.3 cm ( = 21.8 inches )

Air Blast:

What does this mean?

The air blast will arrive approximately 5.05 minutes after impact.
Peak Overpressure: 7.19e+06 Pa = 71.9 bars = 1020 psi
Max wind velocity: 2140 m/s = 4790 mph
Sound Intensity: 137 dB (Dangerously Loud)
Damage Description:

Tell me more...

Click here for a pdf document that details the observations, assumptions, and equations upon which this program is based. It describes our approach to quantifying the important impact processes that might affect the people, buildings, and landscape in the vicinity of an impact event and discusses the uncertainty in our predictions. The processes included are: atmospheric entry, impact crater formation, fireball expansion and thermal radiation, ejecta deposition, seismic shaking, and the propagation of the atmospheric blast wave.

Recent improvements in the airblast calculation are described here.

Earth Impact Effects Program Copyright 2004, Robert Marcus, H.J. Melosh, and G.S. Collins
These results come with ABSOLUTELY NO WARRANTY