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: 58.00 km ( = 36.00 miles )

Projectile diameter: 140.00 meters ( = 459.00 feet )

Projectile Density: 8000 kg/m³

Impact Velocity: 30.00 km per second ( = 18.60 miles per second )

Impact Angle: 90 degrees

Target Density: 2500 kg/m³

Target Type: Sedimentary Rock

Energy:

Energy before atmospheric entry: 5.17 x 10¹⁸ Joules = 1.24 x 10³ MegaTons TNT

The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 3.8 x 10⁴years

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 23300 meters = 76300 ft

The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 29.4 km/s = 18.3 miles/s

The energy lost in the atmosphere is 1.95 x 10¹⁷ Joules = 4.66 x 10¹ MegaTons.

The impact energy is 4.98 x 10¹⁸ Joules = 1.19 x 10³MegaTons.

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 0.239 km by 0.239 km

Crater Dimensions:

What does this mean?

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

Transient Crater Diameter: 4.52 km ( = 2.81 miles )

Transient Crater Depth: 1.6 km ( = 0.993 miles )

Final Crater Diameter: 5.54 km ( = 3.44 miles )

Final Crater Depth: 495 meters ( = 1620 feet )

The crater formed is a complex crater.

The volume of the target melted or vaporized is 0.0443 km³ = 0.0106 miles³

Roughly half the melt remains in the crater, where its average thickness is 2.76 meters ( = 9.04 feet ).

Thermal Radiation:

What does this mean?

Time for maximum radiation: 116 milliseconds after impact

Visible fireball radius: 3.15 km ( = 1.96 miles )

The fireball appears 12.3 times larger than the sun

Thermal Exposure: 6.37 x 10⁵ Joules/m²

Duration of Irradiation: 44.4 seconds

Radiant flux (relative to the sun): 14.4

Effects of Thermal Radiation:

Much of the body suffers first degree burns

Seismic Effects:

What does this mean?


The major seismic shaking will arrive approximately 11.6 seconds after impact.

Richter Scale Magnitude: 6.7

Mercalli Scale Intensity at a distance of 58 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 1.82 minutes after the impact.

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

Average Ejecta Thickness: 1.92 cm ( = 0.755 inches )

Mean Fragment Diameter: 14.5 cm ( = 5.72 inches )

Air Blast:

What does this mean?


The air blast will arrive approximately 2.93 minutes after impact.

Peak Overpressure: 23000 Pa = 0.23 bars = 3.26 psi

Max wind velocity: 49.5 m/s = 111 mph

Sound Intensity: 87 dB (Loud as heavy traffic)

Damage Description:

Interior partitions of wood frame buildings will be blown down. Roof will be severely damaged.

Glass windows will shatter.

About 30 percent of trees blown down; remainder have some branches and leaves blown off.

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.