Simulation of Asteroid/Comet Impacts with Earth

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Simulation 1047: One hundred thousand years, looking at worst event each decade.
By Michael Paine 18 Feb 2000

This page provide further information about the simulation described in Benny Peiser's AAAS paper.MSNBC: Adding up the risks of cosmic impact: Researchers turn attention to smaller, more frequent blasts (interview with Benny Peiser and David Morrison). See also my Explorezone/ article "SIMULATING ARMAGEDDON ON YOUR PC: ASTEROID IMPACTS WITH EARTH".

If you have a copy of the software check out, and contribute to, the Users Page.

The computer program is available on diskette distributed with the book "Comet and Asteroid Impact Hazards on a Populated Earth" by John S. Lewis, Academic Press. It was released late in 1999. See review.

Due to its random nature, each time the program is run it generates a completely different set of results. As described below, the overwhelming influence of a few horrendous events means that the total number of fatalities can vary considerably between successive runs.

As John Lewis points out in his book, the hazard from small Near Earth Objects (NEOs) has been underestimated in the past because 'average' properties were used in the estimates. His program simulates a mix of asteroid/comet types, speeds and entry angles. The strong iron asteroids are more likely to do damage than the 'average' stony asteroid. Also an object with a shallow entry angle is more likely to slow down without breaking up, and therefore reach a lower altitude where it is more destructive.

Set out below are the results of a total of one hundred thousand years of simulation, looking at the worst event in each of 10,000 decades. I want to stress that these are NOT predictions and that no known NEOs are on a collision course with Earth. There is also a page with the results of a one million year simulation.

The original program uses a tsunami runup factor of 30 (the height of the wave at the shoreline was assumed to be 30 times the height of the wave in deep water). A more conservative runup factor of 5 was used in the simulation.

The program is mainly intended for runs covering a several thousand years. In these time periods impacts massive enough to cause global climatic trauma are extremely rare and the program did not fully account for these effects. Lewis and others suggest an explosion equivalent to one million megatons of TNT would be sufficient to cause over a billion human fatalities, mainly due to global starvation. A typical asteroid about 1 mile across would do the trick. Global climatic effects probably become insignificant for asteroids smaller than 500 yards across, with a typical explosion of 10,000 megatons of TNT (some 200 times larger than an H-bomb). The potential fatalities from these climatic effects have been included in the following fatality estimates.

Asteroid/comet diameter is estimated from mass (randomly generated by the program) and density (derived from the type of object - also randomly generated).

A constant world population of 5 billion people is assumed. It is also assumed that impacts occur without warning (the current situation) and that there is no time for evacuation or preparation, such as stockpiling of food supplies.

The big one!

The largest impact recorded over the 100,000 year run was a stony asteroid 5 kilometres in diameter travelling at 29 kilometres per second. The 23 million megaton explosion produced a crater 60 kilometres across and the resulting climate catastrophe was sufficient to wipe out the human population. Fortunately there is only an estimated 1 in 500 chance of such an event occurring during  100,000 years of simulation. This event was ignored for the current analysis, which was intended to
give an idea of "typical" impacts over a 10,000 year period.

Size of asteroid/comet

Asteroid/ comet diameter
No. of events No. of fatal events % Fatal Average yield of fatal
(Mt TNT)
Average fatalities per fatal event Annual risk of fatal event
13-99 9792 949 10% 18 43 000 1 in 100
100-199 173 124  72% 300 280 000 1 in 800
200-499 31 29 94% 2000 700 000 1 in 3500
500-999 3 3 100% 35 000 13 million 1 in 30 000
All 9999* 1105 11% 170 120 000 1 in 90
* Ignoring the 23 million Mt event

Type of impactor

15% of the fatal events were due to long period comets, 6% were due to short period comets and the remainder were due to asteroids. The proportion of comets was much lower than that with the one million year simulation, over which several catastrophic comet impacts can be expected.

Type of impact

Type of impact No. of events No. of fatal events (%)  Average fatalities
per fatal event
Airburst over land  2850 834 (28%) 80 000
Land impact with crater 40 38 (95%) 400 000
Airburst over ocean 6760 120 (2%) 32 (shipping)
Ocean impact with tsunami   119 114 (96%)  470 000
Excludes events where the object skipped out of the Earth's atmosphere.


Over the 100,000 year simulation only 40 land craters were produced. 38 of these resulted in fatalities. In other words out of a total of 1105 fatal events only 3% resulted in a land crater. Furthermore, many of these craters would be eroded or buried over a few thousand years. .Land craters are therefore a very poor indicator of the hazard due to comets and asteroids.

Note that small craters resulting from the impact of fragments are not counted.
Crater Diameter (km)  No. of craters
Less than 1 km 9
1 to 1.9km 14
2 to 4.9km  15
5km or more 2

What can be expected in a typical 10,000 years?

Dividing the results of this simulation by 10 will give us an idea of a "typical" 10,000 years. With a constant human population of 5 billion cosmic impacts over 10,000 years can be expected to produce:

If there were no reliable human records of the 110 fatal events then the only strong physical evidence for the cause of 13 million fatalities would be 4 impact craters, if they had not been eroded or buried.

More stats

Here are some further stats for the 100,000 years in decade steps. There may be some slight disagreements with the values shown in the tables above due to the filters applied.



EVENT                Count of decades where the worst incident was in  the range
DIA_M                Mean diameter of impactors
DIA_M                Std. Dev. of diameter of impactor
ENGY_MT              Mean kinetic energy at entry to atmosphere Mt TNT
CRATER_KM            Max crater diameter in km
YIELD_MT             Mean explosive yield Mt TNT
BLASTFAT             Sum of blast fatalities
FIREFAT              Sum  of firestorm fatalities
TSUFAT               Sum of tsunami fatalities
GLASFAT              Sum of glass fatalities (if they survive blast and firestorm)
DUSTFAT#             Sum of climate-change fatalities (my addition to program)
TOTFAT#              Sum of all fatalities

NEOS 13 to 49m in DIAMETER (smallest for fatality 14m, most were irons)

EVENT                Count                         8955 (666 Fatal)
DIA_M                Mean                         26.44
DIA_M                Std. Dev.                     7.55
ENGY_MT              Mean                          2.89
CRATER_KM            Max                              0
YIELD_MT             Mean                          2.82
BLASTFAT             Sum                         220567
FIREFAT              Sum                        7050187
TSUFAT               Sum                             43
GLASFAT              Sum                           2153
DUSTFAT#             Sum                           0.00
TOTFAT#              Sum                     7272945

NEOS 50 to 99m in DIAMETER

EVENT                Count                          837 (317 Fatal)
DIA_M                Mean                         65.16
DIA_M                Std. Dev.                    13.05
ENGY_MT              Mean                         37.48 Mt
CRATER_KM            Max                              1 (iron)
YIELD_MT             Mean                         36.42 Mt
BLASTFAT             Sum                        2619067
FIREFAT              Sum                       31816799
TSUFAT               Sum                         186597
GLASFAT              Sum                              0
DUSTFAT#             Sum                           0.00
TOTFAT#              Sum                    34622464

NEOS 100 to 199m DIA

EVENT                Count                          173 (125 fatal)
DIA_M                Mean                        132.96
DIA_M                Std. Dev.                    26.87
ENGY_MT              Mean                        351.46
CRATER_KM            Max                              3
YIELD_MT             Mean                        350.33
BLASTFAT             Sum                        6648347
FIREFAT              Sum                       20743470
TSUFAT               Sum                        7244506
GLASFAT              Sum                              0
DUSTFAT#             Sum                           0.00
TOTFAT#              Sum                    34636322

NEOs 200 to 499m DIA

EVENT                Count                           31 (29 fatal)
DIA_M                Mean                        261.35
DIA_M                Std. Dev.                    45.18
ENGY_MT              Mean                       2392.14
CRATER_KM            Max                              7
YIELD_MT             Mean                       2391.29
BLASTFAT             Sum                       12081152
FIREFAT              Sum                              0
TSUFAT               Sum                        3883049
GLASFAT              Sum                              0
DUSTFAT#             Sum                     3298108.00
TOTFAT#              Sum                    19262310

NEOS 500 to 999m DIA

EVENT                Count                            3 (all fatal!)
DIA_M                Mean                        707.67
DIA_M                Std. Dev.                   206.65
ENGY_MT              Mean                      22779.13
CRATER_KM            Max                              9
YIELD_MT             Mean                      22788.50
BLASTFAT             Sum                              0
FIREFAT              Sum                              0
TSUFAT               Sum                          28884
GLASFAT              Sum                              0
DUSTFAT#             Sum                    39072387
TOTFAT#              Sum                    39101271


EVENT                Count                         2850 (834 fatal)
DIA_M                Mean                         30.67 (44.6 for fatals, Max 184)
DIA_M                Std. Dev.                    16.28
ENGY_MT              Mean                          9.81
CRATER_KM            Max                              0
YIELD_MT             Mean                          9.79 (28.3 for fatals)
BLASTFAT             Sum                        6686741
FIREFAT              Sum                       59606680
TSUFAT               Sum                              0
GLASFAT              Sum                           2140
DUSTFAT#             Sum                           0.00
TOTFAT#              Sum                    66295562


Lewis J.S. (1999). Comet and Asteroid Impact Hazards on a Populated
Earth. Academic Press, San Diego.

Paine M. (1999) 'Asteroid Impacts: the Extra Hazard Due to Tsunami', The
Science of Tsunami Hazards 17-3, 155-166. The Tsunami Society, Hawaii.