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: 10.00 km ( = 6.21 miles )

Projectile diameter: 45.00 meters ( = 148.00 feet )

Projectile Density: 8000 kg/m³

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

Impact Angle: 80 degrees

Target Density: 2500 kg/m³

Target Type: Sedimentary Rock

Energy:

Energy before atmospheric entry: 7.63 x 10¹⁶ Joules = 1.82 x 10¹ MegaTons TNT

The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 1.6 x 10³years

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 16800 meters = 55000 ft

The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 16.3 km/s = 10.1 miles/s

The energy lost in the atmosphere is 2.54 x 10¹⁶ Joules = 6.07 x 10⁰ MegaTons.

The impact energy is 5.09 x 10¹⁶ Joules = 1.22 x 10¹MegaTons.

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 0.175 km by 0.173 km

Crater Dimensions:

What does this mean?

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

Transient Crater Diameter: 1.43 km ( = 0.89 miles )

Transient Crater Depth: 507 meters ( = 1660 feet )

Final Crater Diameter: 1.79 km ( = 1.11 miles )

Final Crater Depth: 381 meters ( = 1250 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 177 meters ( = 580 feet ).

The volume of the target melted or vaporized is 446000 m³ = 1.58e+07 feet³

Roughly half the melt remains in the crater

Thermal Radiation:

What does this mean?

Time for maximum radiation: 45.4 milliseconds after impact

Visible fireball radius: 733 meters ( = 2410 feet )

The fireball appears 16.7 times larger than the sun

Thermal Exposure: 2.40 x 10⁵ Joules/m²

Duration of Irradiation: 9.63 seconds

Radiant flux (relative to the sun): 24.9 (Flux from a burner on full at a distance of 10 cm)

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 2 seconds after impact.

Richter Scale Magnitude: 5.3

Mercalli Scale Intensity at a distance of 10 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?

Most ejecta is blocked by Earth's atmosphere

Air Blast:

What does this mean?


The air blast will arrive approximately 30.3 seconds after impact.

Peak Overpressure: 34700 Pa = 0.347 bars = 4.92 psi

Max wind velocity: 71.7 m/s = 160 mph

Sound Intensity: 91 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.