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: 20000.00 km ( = 12400.00 miles )

Projectile diameter: 180.00 meters ( = 590.00 feet )

Projectile Density: 1000 kg/m³

Impact Velocity: 31.00 km per second ( = 19.30 miles per second )

Impact Angle: 90 degrees

Target Density: 2500 kg/m³

Target Type: Sedimentary Rock

Energy:

Energy before atmospheric entry: 1.47 x 10¹⁸ Joules = 3.51 x 10² MegaTons TNT

The average interval between impacts of this size somewhere on Earth during the last 4 billion years is 1.1 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 90300 meters = 296000 ft

The projectile reaches the ground in a broken condition. The mass of projectile strikes the surface at velocity 17.2 km/s = 10.7 miles/s

The energy lost in the atmosphere is 1.02 x 10¹⁸ Joules = 2.42 x 10² MegaTons.

The impact energy is 4.52 x 10¹⁷ Joules = 1.08 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 0.735 km by 0.735 km

Crater Dimensions:

What does this mean?

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

Transient Crater Diameter: 2.17 km ( = 1.35 miles )

Transient Crater Depth: 768 meters ( = 2520 feet )

Final Crater Diameter: 2.72 km ( = 1.69 miles )

Final Crater Depth: 578 meters ( = 1900 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 268 meters ( = 879 feet ).

The volume of the target melted or vaporized is 0.00403 km³ = 0.000966 miles³

Roughly half the melt remains in the crater

Thermal Radiation:

What does this mean?

The fireball is below the horizon. There is no direct thermal radiation.

Seismic Effects:

What does this mean?


The major seismic shaking will arrive approximately 1.11 hours after impact.

Richter Scale Magnitude: 6.0

Mercalli Scale Intensity at a distance of 20000 km:

Nothing would be felt. However, seismic equipment may still detect the shaking.

Ejecta:

What does this mean?

Little rocky ejecta reaches this site; fallout is dominated by condensed vapor from the projectile.

Air Blast:

What does this mean?


The air blast will arrive approximately 16.8 hours after impact.

Peak Overpressure: 17 Pa = 0.00017 bars = 0.00241 psi

Max wind velocity: 0.04 m/s = 0.0894 mph

Sound Intensity: 25 dB (Easily Heard)

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.