Sections · Impacts

Vol. Science · Astronomy · The crater

Impacts
and the scale

A diameter and a speed are an energy, and an energy is not yet a crater. The mass of a sphere is m = π/6 · ρ · L³. The kinetic energy at the speed you set is E = ½mv². One megaton of TNT on this page is 4.184 × 10¹⁵ J. Collins, Melosh, and Marcus print 4.18 × 10¹⁵ J. The transient crater and the final rim are their pi-scaling, equations 21, 22, and 27 in the 2005 Earth Impact Effects Program paper. The angle is measured from the horizontal. 45° is the most probable angle in that program. The velocity floor is escape speed: the Earth Fact Sheet lists 11.186 km/s, and the program’s minimum template is 11.2 km/s. Typical asteroid encounters in the paper are 12–20 km/s. The program’s typical-asteroid template is 17 km/s. The top of the slider is 72 km/s, their maximum for an object bound to the Sun. Speed on an orbit is the vis-viva desk. The coasting speed that leaves a body is the escape desk. A grain that becomes a streak, not a crater, is the meteor desk.

Educational calculator. Simplified scaling. Order-of-magnitude estimates. Not a hazard assessment, not a damage map, and not a statement that a crater forms. The paper says the leading constants are a best estimate inside 0.8 to 1.5, not known to three decimal places. This page does not compute an airburst altitude. For a real near-Earth object, use NASA CNEOS and the Planetary Defense Coordination Office.

Interactive · Energy and crater scaling

Final rim beside a cited length · same scale

This scaling
Cited length

The page opens on a Barringer-like case: 42 m of iron at 15 km/s. The Earth Impact Database rim is 1.186 km.

Cases · cited inputs, not reconstructions

Density · program templates

Target · Collins et al. densities

Diameter m

Speed km/s

Angle deg

Barringer-like · simple crater · schematic

1.46 km

Final rim · eq. 22 · sedimentary rock

Mass3.103×10^8 kg
Energy3.491×10^16 J
Megatons8.34 Mt
Recurrence570 years
Transient1.17 km
Final rim1.46 km
KindSimple
Constant band1.01–1.89 km

Equation 21 gives a transient crater of 1.17 km at the pre-impact surface. Under 2.56 km, equation 22 multiplies by 1.25, so the final rim is 1.46 km. The Earth Impact Database rim is 1.186 km. That cited rim sits inside the paper’s 0.8–1.5 range on the leading constant.

8.34 Mt uses 4.184 × 10^15 J. Collins et al. 2016, as corrected by Kring, is 8.6 Mt for a heavier iron mass at the same 42 m and 15 km/s. The whole-Earth recurrence from their equation 3 is about 570 years at this energy.

42 m is under the 1 km cutoff, so Collins et al. would run their entry procedure. Iron is the strong end of that relation. A small, strong body can reach the ground intact in their account. This page does not compute the airburst altitude.

The sliders need JavaScript. The relations are still m = π/6 · ρ · L³, E = ½mv², 1 Mt = 4.184 × 10^15 J, and Collins et al. 2005 equations 21, 22, and 27. Equation 3 is the recurrence, about 109 × E^0.78 years for E in megatons. For 42 m of iron at 8000 kg/m³, 15 km/s, 45°, and sedimentary rock at 2500 kg/m³, the transient crater is 1.17 km and the final rim is 1.46 km. The Earth Impact Database rim of Barringer is 1.186 km. Kring’s table of the Collins et al. 2016 model is 8.6 Mt at a slightly higher mass. Not a hazard assessment.

What the scaling does

A sphere, a speed, and two diameters.

Energy. The speed on the slider is the speed in ½mv². In the paper that speed, called v₀, is the speed at the top of the atmosphere. The crater formulas use the speed at the surface after the atmosphere has had its say. For a body of 1 km or larger, Collins et al. say entry has no significant influence, so the two speeds are the same in their treatment. Under 1 km, this page still drops the slider speed straight into equation 21. It does not slow the body down. The crater number is what the scaling says if that speed is the surface speed.

Transient crater. Equation 21 is D_tc = 1.161 (ρ_i/ρ_t)^1/3 L^0.78 v^0.44 g_E^−0.22 sin^1/3θ, with L in meters, v in meters per second, and D_tc in meters, measured at the pre-impact surface. g_E here is 9.81 m/s². For water the 1.161 becomes 1.365. The paper says both constants are a best estimate inside 0.8 to 1.5.

Final rim. If the transient crater is 2.56 km or smaller, equation 22 is D_fr ≈ 1.25 D_tc. Above 2.56 km, equation 27 is D_fr = 1.17 D_tc^1.13 / D_c^0.13, with D_c = 3.2 km and both diameters in kilometers. The two pieces do not meet exactly at the join. Water does not get either collapse law. The program’s marine target also has a rock seafloor under a water depth. This desk has no water depth, so the water button is only the water-layer cavity.

Cases · what is cited, and what is a default

Preset inputs and the ranges around them
Button	Set on the sliders	Published range
Chelyabinsk · 2013	18 m, dense rock 3000 kg/m³, 18.6 km/s, 45°, sedimentary. The 18 m and 18.6 km/s are the JPL additional-details estimates. The density, the angle, and the target are not.	The same JPL page updates the size to 17 m and the energy to nearly 500 kilotons, after first printing about 18 m, about 11,000 tons, and 440 kilotons. Brown et al. 2013: about 19 m, with a 17–20 m range, and 500 ± 100 kilotons. Peak brightness at 23.3 km in the JPL account. An airburst, not a crater of the scaled size.
Tunguska · 1908	50 m, dense rock, 17 km/s, 45°, sedimentary. 50 m is the low end of one cited diameter range. 17 km/s and 45° are program defaults, not a measured entry.	NASA/TM–2018 (NTRS 20190002302), abstract: models converged on 10–20 megatons, an airburst at about 10 km, and no crater. If the body was a stony asteroid like Chelyabinsk, the diameter was roughly 50–80 m. The same memorandum also records other diameter bands from the talks. There is no single Tunguska diameter.
Barringer	42 m, iron 8000 kg/m³, 15 km/s, 45°, sedimentary. 42 m and 15 km/s are the Collins et al. 2016 surface-impact case in Kring’s table. 8000 kg/m³ is the program’s iron template. 45° is the most probable angle, not a measured trajectory.	Kring (2017) corrects that model to 3.2 × 10⁸ kg and 8.6 Mt. This button’s 8000 kg/m³ sphere is a little lighter, so the megatons are this page’s arithmetic. Earth Impact Database, via the Meteoritical Bulletin: rim 1.186 km, age 0.049 ± 0.003 Ma. USGS Astrogeology also says 1.2 km and 180 m deep, and its caption still quotes an older approximate impactor of about 30 m at 12–20 km/s and over 2 million tons of TNT. Kring’s table runs from a fraction of a megaton to over 60.
Chicxulub	14 km, dense rock, 17 km/s, 45°, sedimentary. 14 km is the Earth Impact Effects Program’s diameter template labeled Chicxulub. The speed, the angle, and the rock target are defaults.	Morgan et al. 2022: the structure is approximately 200 km across, the impact was oblique, and the energy is about 10²³ J. They do not, in that review, assign one impactor diameter. The real target was a shallow sea. This button does not model that water layer.

Literacy · the words on the readout

Megaton: This page divides joules by 4.184 × 10¹⁵. Collins et al. print 4.18 × 10¹⁵. Brown et al. 2013 use 4.185 × 10¹² J per kiloton. The three differ by about a tenth of a percent, which is smaller than the crater-scaling band.
Angle: Degrees from the horizontal, the way the paper measures θ. A vertical impact is 90°. Equation 21 scales the transient crater with sin^1/3θ, so 45° is smaller than vertical. The program calls 15° the shallowest angle it associates with a circular crater. The slider still runs down to 5° and says the scaling is the same formula.
Recurrence: Equation 3, T_RE ≈ 109 E^0.78 years, E in megatons, somewhere on Earth. It is their fit to the Near-Earth Object Science Definition Team (2003) size distribution. It is not a forecast for one place. The 2018 NASA Tunguska workshop concluded that the interval between Tunguska-class events is millennia, not centuries. This line stays the 2005 fit.
Atmosphere: Collins et al. apply their breakup procedure only under 1 km. Above that, they say entry does not significantly change the body’s energy. Under 1 km, breakup begins when ram pressure exceeds strength. Strength in their program rises with density from 1000 to 8000 kg/m³. Cometary ice is the weak end. Iron is the strong end, and a small, strong body can reach the ground intact. They define an airburst as the altitude where the body has spread to seven times its original diameter. This desk does not solve that altitude.
What the rim leaves out: Drag, ablation, a strewn field, melt, ejecta, shaking, and the blast wave are all in the 2005 program and not on this page. The gravity-regime scaling is meant for craters larger than a couple of hundred meters. A final rim under that is an extrapolation. The constant band is only the paper’s 0.8–1.5 range on the leading factor, carried through the same exponents. It is not a full error bar. Comparing a fresh rim-to-rim diameter with an eroded terrestrial structure needs the caution the paper already gives.

Sources · the formulas and the presets

Cited, not invented

Collins, Melosh, and Marcus, Meteoritics & Planetary Science 40, 817–840 (2005) — Earth Impact Effects Program. Equation 1 is the kinetic energy, π/12 · ρ · L³ · v², which is ½mv² for a sphere. They print 1 Mt = 4.18 × 10¹⁵ J. Equation 3 is T_RE ≈ 109 E^0.78 years. Equation 21 is the transient crater, constant 1.161 in rock and 1.365 in water, proportional to sin^1/3θ. Equation 22 is D_fr ≈ 1.25 D_tc for a simple crater. Equation 27 is the complex-crater rim, used when the transient diameter is greater than 2.56 km, with D_c = 3.2 km. Target densities: sedimentary 2500, crystalline 2750, water 1000, and a marine seafloor at 2700 that this page does not model. Rocky asteroids about 2000–3000 kg/m³, iron about 8000, comets about 500–1500. Asteroid speeds about 12–20 km/s. Comet speeds about 30–70 km/s. Maximum for a body bound to the Sun, 72 km/s. Their entry procedure is only for impactors under 1 km. The constants 1.161 and 1.365 are a best estimate inside 0.8 to 1.5.
Earth Impact Effects Program — the same authors’ calculator. Density templates: 1000 ice, 1500 porous rock, 3000 dense rock, 8000 iron. Speed templates: minimum 11.2 km/s, typical asteroid 17 km/s, typical comet 51 km/s, maximum 72 km/s. Most probable angle 45°. Diameter templates used as familiar lengths here: double-decker bus 5 m, Chelyabinsk 20 m, Nelson’s Column 52 m, Queen’s Tower 87 m, Wembley Stadium 320 m, Ben Nevis 1.3 km, Jersey 10 km, Isle of Wight 20 km, and a Chicxulub template of 14 km. The program’s 20 m Chelyabinsk template is not the JPL estimate.
NASA NSSDCA — Earth Fact Sheet — escape velocity 11.186 km/s. Volumetric mean radius 6,371.000 km, so the diameter drawn as a familiar length is 12,742 km. Mean surface gravity 9.820 m/s². Equation 21 on this page uses 9.81 m/s². The −0.22 power makes that difference negligible.
NASA JPL — Additional details on the 15 February 2013 fireball — about 18 m, about 11,000 tons, 18.6 km/s, peak brightness at 23.3 km, about 440 kilotons. An update on the same page revises the estimate to 17 m, 10,000 tons, and nearly 500 kilotons. The fragments are ordinary chondrites. This page does not assign them a measured bulk density.
Brown and others, Nature 503, 238–241 (2013) — Chelyabinsk about 19 m, the range they print is 17–20 m, energy about 500 ± 100 kilotons. They take 1 kiloton of TNT as 4.185 × 10¹² J.
Morrison, NASA/TM–2018, Tunguska workshop (NTRS 20190002302) — abstract: 10–20 megatons, airburst height about 10 km, and, for a stony body like Chelyabinsk, a diameter of roughly 50–80 m. The interval between such events is millennia, not centuries. No crater. Talks inside the same memorandum quote other diameter bands. The 50 m button is the low end of the abstract’s range, not a preferred reconstruction.
Kring, LPI Contribution 2040, chapter 11 (2017) — Barringer energies in the literature run from a fraction of a megaton to over 60. The Collins et al. 2016 row, with Kring’s mass correction, is a 42 m projectile, 15 km/s, 3.2 × 10⁸ kg, and 8.6 Mt. Artemieva’s disruption cases in the same table are different diameters and speeds, around 10–11 Mt in the 2006 row and 7–15 Mt in 2009. This page’s iron density is the program’s 8000 kg/m³, not that 3.2 × 10⁸ kg.
Meteoritical Bulletin — Barringer — writeup from the Earth Impact Database: D = 1.186 km, age 0.049 ± 0.003 Ma.
USGS Astrogeology — Meteor Crater sample collection — 1.2 km diameter, 180 m deep, formed about 50,000 years ago. The caption also gives an approximate impactor of about 30 m at 12–20 km/s and an energy of over 2 million tons of TNT. That caption and the Kring table are not the same estimate. Both are cited. The button follows the 42 m, 15 km/s model.
Morgan, Bralower, Brugger, and Wünnemann, Nature Reviews Earth & Environment (2022) — Chicxulub is an approximately 200 km structure. The asymmetric shape suggests an oblique impact and an energy of about 10²³ J. The 14 km button is the program template, not a figure from this review.
NASA CNEOS and NASA Planetary Defense — where a real close approach is tracked. This desk is not that catalog.

Classroom scaling. Not a hazard assessment. The Barringer-like rim on the opening view is equation 22 at 42 m, 8000 kg/m³, 15 km/s, 45°, and sedimentary rock. It is 1.46 km. The database rim is 1.186 km, inside the paper’s constant band for that case. Earthrise preview: NASA / Bill Anders (public domain).

Keep going

The streak

Two circles	The scaling and the nearest cited length, when they are within a factor of eight of each other. Same meters per pixel.
One circle	When the comparison would be a speck or would overflow. The sentence under the drawing still names the length.
Scale bar	A round length in meters or kilometers. It is a ruler, not a second crater.

Chart	Left and Right step the log diameter while the canvas is focused. Up and Down step the angle by one degree.
Buttons	Enter or Space selects. The pressed button is aria-pressed. Targets are at least 44 pixels on a side.
Phone	Below 900 pixels the long section row becomes a single Sections control. Open it for the same links. The site menu is the Menu button in the top bar.
This dialog	The question mark, or ?, opens it. Escape closes it. Tab stays inside until you close it. Click the dim page behind the card to close it.

Impacts
and the scale

A sphere, a speed, and two diameters.

Cited, not invented

Meteors

Escape

Vis-viva

CNEOS

Black holes

Gravity

Impact desk

Inputs

Drawing

Keyboard and touch

Cases	Each button sets a cited diameter and, where the source gives one, a cited speed. Density, angle, and target stay on program defaults when the papers do not agree on a single value. The table under the calculator says which is which.
Density	1000, 1500, 3000, or 8000 kg/m³. Those are the program’s templates. The 2005 paper’s ranges are wider.
Target	Sedimentary 2500, crystalline 2750, or water 1000. Water changes the leading constant from 1.161 to 1.365 and skips the rock collapse.
Diameter	Log slider from 1 m to 15 km. The number field accepts the same range.
Speed	11.2 to 72 km/s on the slider. A typed value may sit on the fact-sheet escape speed, 11.186 km/s, and no lower.
Angle	5° to 90° from the horizontal. 45° is the default.

Impactsand the scale

A sphere, a speed, and two diameters.

Cited, not invented

Meteors

Escape

Vis-viva

CNEOS

Black holes

Gravity

Impacts
and the scale