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: 650.00 meters ( = 2130.00 feet )

Projectile Density: 3000 kg/m³

Impact Velocity: 35.00 km per second ( = 21.70 miles per second )

Impact Angle: 60 degrees

Target Density: 2500 kg/m³

Target Type: Sedimentary Rock

Energy:

Energy before atmospheric entry: 2.64 x 10²⁰ Joules = 6.31 x 10⁴ MegaTons TNT

The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 5.5 x 10⁵years

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 begins to breakup at an altitude of 65600 meters = 215000 ft

The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 34.7 km/s = 21.5 miles/s

The energy lost in the atmosphere is 4.68 x 10¹⁸ Joules = 1.12 x 10³ MegaTons.

The impact energy is 2.60 x 10²⁰ Joules = 6.20 x 10⁴MegaTons.

The larger of these two energies is used to estimate the airblast damage.

The broken projectile fragments strike the ground in an ellipse of dimension 0.926 km by 0.802 km

Crater Dimensions:

What does this mean?

Crater shape is normal in spite of atmospheric crushing; fragments are not significantly dispersed.

Transient Crater Diameter: 11.1 km ( = 6.88 miles )

Transient Crater Depth: 3.91 km ( = 2.43 miles )

Final Crater Diameter: 15.2 km ( = 9.45 miles )

Final Crater Depth: 672 meters ( = 2200 feet )

The crater formed is a complex crater.

The volume of the target melted or vaporized is 2 km³ = 0.48 miles³

Roughly half the melt remains in the crater, where its average thickness is 20.8 meters ( = 68.2 feet ).

Thermal Radiation:

What does this mean?

Time for maximum radiation: 368 milliseconds after impact

Visible fireball radius: 12 km ( = 7.43 miles )

The fireball appears 27.2 times larger than the sun

Thermal Exposure: 1.14 x 10⁷ Joules/m²

Duration of Irradiation: 2.76 minutes

Radiant flux (relative to the sun): 68.9

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 20 seconds after impact.

Richter Scale Magnitude: 7.8

Mercalli Scale Intensity at a distance of 100 km:

VII. Damage negligible in buildings of good design and construction; slight to moderate in well-built ordinary structures; considerable damage in poorly built or badly designed structures; some chimneys broken.

VIII. Damage slight in specially designed structures; considerable damage in ordinary substantial buildings with partial collapse. Damage great in poorly built structures. Fall of chimneys, factory stacks, columns, monuments, walls. Heavy furniture overturned.

Ejecta:

What does this mean?


The ejecta will arrive approximately 2.4 minutes after the impact.

At your position there is a fine dusting of ejecta with occasional larger fragments

Average Ejecta Thickness: 13.4 cm ( = 5.28 inches )

Mean Fragment Diameter: 9.73 cm ( = 3.83 inches )

Air Blast:

What does this mean?


The air blast will arrive approximately 5.05 minutes after impact.

Peak Overpressure: 98800 Pa = 0.988 bars = 14 psi

Max wind velocity: 171 m/s = 383 mph

Sound Intensity: 100 dB (May cause ear pain)

Damage Description:

Multistory wall-bearing buildings will collapse.

Wood frame buildings will almost completely collapse.

Glass windows will shatter.

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.