1. Near-Earth objects – a threat for Earth?
Or: NEOs for engineers and physicists
Lecture 8 – Impact effects and consequences
Dr. D. Koschny (ESA)
Prof. Dr. E. Igenbergs (LRT)
Image credit: ESA

2. Context NEOs Minor Planet Center (US) ESA others SSA tasking centre
Political entities
National Cooperatingtelescopes
SSA sensors
Space missions
- Risk assessment
Obs. Planning
Phys. Properties
SSA-NEO Coordination Centre
- Databases
- Light curves
- Shape models
General users
Space mission studies
National research expertise
NEO image credit: JAXA
SSA-NEO-ESA-DR-0017/1.6, 16 Jan 2014 2

3. Impact craters on Earth
Nördlinger Ries
25 km, 15 Mio years
Meteor crater in Arizona
1.2 km, years 50 m iron impactor

4. Arizona Meteor Crater – 50000 yrs ago (in 2013)

5. Arizona Meteor Crater – 50000 yrs ago (in 2013)

6. The Tunguska event - 1908 June 1908 - >100 years ago
2000 km2 Taiga destroyed in Siberia
30-40 m stony object exploded in ~40 km height

7. Sikote Alin - 1947 Primorsky Krai, Russia, 12 Feb 1947
120 craters and impact pits
Largest crater 26.5 m
Iron object, t mass, 2-3 m diameter

8. Carancas
Crater with 14 m diameter –formed by an impact from space in 2007, Carancas, Peru.

9. Carancas
Carancas impact crater 2007 Credit: Uni Freiburg 9

10. Sudan event 2008 Asteroid 2008 TC3 First predicted hit
(20 h in advance) 2-5 m, atmospheric explosion
Image: Eumetsat 10

11. Sudan event 2008
Image: NASA/Seti/Jenniskens 11

12. Chelyabinsk
15 Feb 2013: A m object enters the atmosphere over Chelyabinsk, Russia. The shock wave of the airburst shatters thousands of windows (and hurts people) 12

13. Chelyabinsk

14. Chelyabinsk

15. Chelyabinsk
Credit: Andrey Orlov. 15

16. Image credit: Michael Farmer 16
Image taken from: russian_divers_salvage_huge_hunk_of_ chelyabinsk_meteorite_from_lake/
Image credit: Michael Farmer 16
Asteroid and meteoroid impacts Apr 2014, IDER, D. Koschny - Page 4

17. A bit more systematically
From the SSA-NEO funded SN-VII study (

18. Possible effects
Following SSASNVII-DMS-TEC-TN01-10-E, Review of impact-related effects:
Atmospheric entry effects
Low altitude atmospheric effects
Water effects
Ground effects
Ejecta and atmospheric effects
Human and economic effects

19. Some criteria Up to 1..10 m: Nice fireball, possible meteorites
1..40 m: Airburst, shock wave, meteorites, possibly thermal wave
>40 m: crater (exception: Carancas was a 1-m object), shock wave, thermal wave, mechanical damage
Earthsky.org, credit Navicore
Youtube.com

20. Assessing the effects Nuclear bomb testing (US, last century)
Experiments in the lab
Small, lower velocity
Use scaling factors
Simulation
How realistic are they? Needs ‘benchmarking’

21. Impact experiments on (porous) pumice targets
Examples kindly provided by Patrick Michel, Obs. Cote d’Azur
With A. Nakamura
New light gas gun (ISAS)
Pumice target (6 cm); V=3 km/s

22. Confrontation simulations/experiments
Jutzi, Michel, Hiraoka, Nakamura, Benz, 2009, Icarus 201
T = 1.5 ms
Experiment
Simulation
First validations of a model of fragmentation of porous body

23. Confrontation simulation/experiments
T = 8 ms
Experiment
Simulation
First application at large scale: formation of
the crater on the asteroid Stein (Rosetta image)
Jutzi, Michel, Benz A&A 509, L2

24. Atmospheric effects – example for numerical simulations
Shuvalov et al., Meteoroids 2016
Top: model – Right: photograph

25. Estimating the energy Reminder:
1 kt TNT = J
Hiroshima bomb = 15 kt TNT
Chelyabinsk had an energy of about 500 kt TNT

26. Some of the effects and how to compute them
Key publications:
Collins, Melosh, Marcus (2005), Earth impact effects program: A web-based computer program for calculating environment consequences of a meteoroid impact on Earth, Meteoritics & Planetary Science 40, Nr. 6,
A lot in there goes back to:
Glasstone and Dolan (1977), The effects of nuclear weapons, 3rd edition. Wash. D.C., United States Department of Defense and Department of Energy. Available here:

27. Crater size
Empirical formula based on laboratory tests and scaling laws
Density of impactor in kg/m3
Diameter of transient crater
Velocity of impactor in m/s
Flight path angle relative to surface
Density of target in kg/m3
Gravitational acceleration (9.81 m/s2)

28. Crater size – rule of thumb
…for large craters on the Earth: Crater diameter = 20 * asteroid diameter

29. Overpressure
Work goes back to nuclear tests performed in the US in the 50ies – published in Glasstone and Dolan, The effects of nuclear weapons (1977).
Cube root scaling – effects scale with cube root of energy, e.g. distance for a given overpressure:

30. Overpressure
Work goes back to nuclear tests performed in the US in the 50ies – published in Glasstone and Dolan, The effects of nuclear weapons (1977).
Cube root scaling – effects scale with cube root of energy, e.g. distance for a given overpressure:
Glasstone + Dolan also give scaling laws for different explosion altitudes

31. More on computing overpressure
Turning point values:
px = Pa;
rx = 290 m
Overpressure in Pa
Distance for 1 kt surface burst
Formula to fit graphs from Glasstone + Nolan derived by Collins et al. 2005

32. More on computing overpressure
Scaling the distance via the cube root scaling law:
Thus:

33. Effects of overpressure
Collins et al. 2005

34. Fireball with radius rfb
Thermal radiation
Luminous efficency – assume
Temperature T ~ ηE
rfb r
Fireball with radius rfb
(from numerical simulations: rfb= rimpactor)

35. Thermal radiation – some formulae
Criterion to incinerate something: T > Tincinerate
Needs certain energy density for a given duration
Thermal exposure: (1)
Duration: (2)
To ignite: (3)
From (1):
Use cube root scaling =>

36. Thermal radiation
Use scaling to compare effects – note that the table gives values for 1 Mt TNT equivalent energies.
Table from Collins et al. 2005

37. Communicating impact effects

38. Earthquake damage – Mercalli scale

39. Earthquake damage -Richter scale

40. Wind damage - Beauford scale

41. Impact hazard scales
Torino scale (1999) – for the public? But not really used
Palermo scale (2002) – for the scientist
Broomfield scale (2014) – not yet official

42. Torino and Palermo scale
IP = Impact Probability
E = Energy released by the impact
DT = Time span until the impact
The Palermo Scale
PS = log10 R
R ~
IP E4/5 DT
PS=10-2 means that the particular impact risk is 1% of the background impact risk until the time of impact.

43. Broomfield scale

44. Summary We have seen some examples for previous impacts
We saw formulae to compute crater size, overpressure, thermal effects – and we saw what the effects are
We learned the currently available ‘hazard scales’ for asteroid impacts – and that they are not really used…

45. Exercises
What is the equivalent energy of the Chelyabinsk asteroid compared to the Hiroshima bomb?
1 kt TNT = J
Hiroshima bomb = 15 kt TNT
Estimated diameter of the asteroid = 20 m
Density: rock
Velocity: 20 km/s
What crater size do you expect for a 50 m iron object hitting Arizona’s desert at 15 km/s?

46. Exercises
(3) Compute the overpressure of the Chelyabinsk airburst – assume it happened at 20 km height and use the result of task (1) for the energy.