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: 687.00 meters ( = 2250.00 feet )

Projectile diameter: 18.00 meters ( = 59.00 feet )

Projectile Density: 20000 kg/m³

Impact Velocity: 20.00 km per second ( = 12.40 miles per second )

Impact Angle: 90 degrees

Target Density: 2750 kg/m³

Target Type: Crystalline Rock

Energy:

Energy before atmospheric entry: 1.22 x 10¹⁶ Joules = 2.92 MegaTons TNT

The average interval between impacts of this size somewhere on Earth is 295.6 years

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.

Atmospheric Entry:

The projectile lands intact, with a velocity 19.3 km/s = 12 miles/s.

The energy lost in the atmosphere is 7.88 x 10¹⁴ Joules = 0.19 x 10⁰ MegaTons.

Crater Dimensions:

What does this mean?

Transient Crater Diameter: 998 meters ( = 3270 feet )

Transient Crater Depth: 353 meters ( = 1160 feet )

Final Crater Diameter: 1.25 km ( = 0.775 miles )

Final Crater Depth: 266 meters ( = 871 feet )

The crater formed is a simple crater

The floor of the crater is underlain by a lens of broken rock debris (breccia) with a maximum thickness of 123 meters ( = 404 feet ).

The volume of the target melted or vaporized is 102000 m³ = 3.59e+06 feet³

Roughly half the melt remains in the crater

Thermal Radiation:

What does this mean?

Time for maximum radiation: 23.3 milliseconds after impact

Visible fireball radius: 450 meters ( = 1480 feet )

The fireball appears 149 times larger than the sun

Thermal Exposure: 1.16 x 10⁷ Joules/m²

Duration of Irradiation: 5.85 seconds

Radiant flux (relative to the sun): 1970

Effects of Thermal Radiation:

Clothing ignites

Much of the body suffers third degree burns

Newspaper ignites

Plywood flames

Deciduous trees ignite

Grass ignites

Seismic Effects:

What does this mean?


The major seismic shaking will arrive approximately 137 milliseconds after impact.

Richter Scale Magnitude: 4.9

Mercalli Scale Intensity at a distance of 0.68715 km:

IV. Felt indoors by many, outdoors by few during the day. At night, some awakened. Dishes, windows, doors disturbed; walls make cracking sound. Sensation like heavy truck striking building. Standing motor cars rocked noticeably.

V. Felt by nearly everyone; many awakened. Some dishes, windows broken. Unstable objects overturned. Pendulum clocks may stop.

Ejecta:

What does this mean?

Most ejecta is blocked by Earth's atmosphere

Air Blast:

What does this mean?


The air blast will arrive approximately 2.08 seconds after impact.

Peak Overpressure: 3.44e+06 Pa = 34.4 bars = 489 psi

Max wind velocity: 1470 m/s = 3290 mph

Sound Intensity: 131 dB (Dangerously Loud)

Damage Description:

Multistory wall-bearing buildings will collapse.

Wood frame buildings will almost completely collapse.

Multistory steel-framed office-type buildings will suffer extreme frame distortion, incipient collapse.

Highway truss bridges will collapse.

Highway girder bridges will collapse.

Glass windows will shatter.

Cars and trucks will be largely displaced and grossly distorted and will require rebuilding before use.

Up to 90 percent of trees blown down; remainder stripped of branches and leaves.

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.