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: 19.30 km ( = 12.00 miles )

Projectile diameter: 150.00 meters ( = 492.00 feet )

Projectile Density: 3000 kg/m³

Impact Velocity: 17.00 km per second ( = 10.60 miles per second )

Impact Angle: 45 degrees

Target Density: 2500 kg/m³

Target Type: Sedimentary Rock

Energy:

Energy before atmospheric entry: 7.66 x 10¹⁷ Joules = 1.83 x 10² MegaTons TNT

The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 1.8 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 54000 meters = 177000 ft

The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 12.6 km/s = 7.83 miles/s

The energy lost in the atmosphere is 3.44 x 10¹⁷ Joules = 8.22 x 10¹ MegaTons.

The impact energy is 4.22 x 10¹⁷ Joules = 1.01 x 10²MegaTons.

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 0.826 km by 0.584 km

Crater Dimensions:

What does this mean?

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

Transient Crater Diameter: 2.11 km ( = 1.31 miles )

Transient Crater Depth: 747 meters ( = 2450 feet )

Final Crater Diameter: 2.64 km ( = 1.64 miles )

Final Crater Depth: 562 meters ( = 1840 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 261 meters ( = 855 feet ).

The volume of the target melted or vaporized is 0.00265 km³ = 0.000637 miles³

Roughly half the melt remains in the crater

Thermal Radiation:

What does this mean?

At this impact velocity ( < 15 km/s), little vaporization occurs; no fireball is created, therefore, there is no thermal radiation damage.

Seismic Effects:

What does this mean?


The major seismic shaking will arrive approximately 3.86 seconds after impact.

Richter Scale Magnitude: 5.9

Mercalli Scale Intensity at a distance of 19.32 km:

VI. Felt by all, many frightened. Some heavy furniture moved; a few instances of fallen plaster. Damage slight.

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.

Ejecta:

What does this mean?


The ejecta will arrive approximately 1.05 minutes after the impact.

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

Average Ejecta Thickness: 2.47 cm ( = 0.971 inches )

Mean Fragment Diameter: 1.25 meters ( = 4.1 feet )

Air Blast:

What does this mean?


The air blast will arrive approximately 58.5 seconds after impact.

Peak Overpressure: 37700 Pa = 0.377 bars = 5.36 psi

Max wind velocity: 77.3 m/s = 173 mph

Sound Intensity: 92 dB (May cause ear pain)

Damage Description:

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.