1. Simulations of the entry and damaging effects of asteroid impacts Planetary Defense Workshop July 6-8 2015 NASA AMES Popova O. 1, Shuvalov V. 1, Jenniskens P. 2, Svetsov V. 1, Glazachev D. 1 Rybnov Y. 1 1 - Institute for Dynamics of Geospheres RAS 2 - SETI Institute

2. Kamensk-Uralskyi, ~175 km North from trajectory Until February 15 2013 the objects ~20 m in size was considered to be safe from the point of view of asteroids hazard

3. Arrival of shock wave

4. People were badly frightened

5. Arrival of shock wave 1612 asked for medical assistance Injuries: - mostly due to flying glass from shattered windows, from walking in and handling glass. - some injuries - from being hit by objects ~100 were hospitalized (39 kids), 2 in serious conditions Web-query respondents reported injuries - due to shock wave arrival: concussion/shell-shock, temporal deafness - due to bright radiation: sunburn, temporal blindness, eyes hurt, retinal burn

6. 500 telephone interviews in Chelyabinsk: were you/your relatives suffered physically or injured, or not ? More than 2% The majority of injuries (1210): - Chelyabinsk (the most populated ), - the highest fraction Korkino ( 0.16% ) ( near trajectory, 7 km from projection ) Many people – didn’t ask for medical assistance 1754 web-queries were collected, 374 ( 21.3% ) – got some injuries (concussion; temporarily deaf/blinded; sunburns etc) The Injuries Assessment

7. Chelyabinsk airburst damage Black line –approximate trajectory Damage took place in 11 municipal districts in Chelyabinsk Oblast (total 27 districts) Area ~250x80 km The largest damage occurred in Chelyabinsk, Korkino and Kopeysk 7 320 buildings were affected;  740 schools and universities,  296 medical facilities,  110 cultural organizations,  48 sport facilities  6 097 apartments buildings and houses

8. Sorry!!! Meteorite consequences!!! Hotel’s door, ~35 km from trajectory School corridor, ~10 km from trajectory Shop, ~60 km from trajectory The extent of the damage was investigated during a field study three weeks after the impact

9. Damage Glasstone & Dolan : 3400-6900 Pa Mannan & Lees,2005: minimal – 0.1-0.2 kPa (jet plane)  p (Pa) 5% 700-1700 50-90% 1600-6900 Data on glass breaking are uncertain  p is dependent on - glass size (large glasses easier), thickness, local effects We accepted:  p~500 Pа just a few windows were broken,  p~1,000 Pa would result in significant damage There was little structural damage, other than broken windows, window frames and doors. One old wall collapsed at a zinc factory.

10. Modeling of Chelyabinsk bolide shock wave The peculiarities of energy release influence on density and pressure distribution in the disturbed area formed in the atmosphere after the entry, and on its subsequent evolution as well as on overpressure on the ground

11. Overpressure at the ground level E1E1 The size of affected area roughly ~ 3 √ E (E 1 >E 2 ) Shape of the area ~ features of assumed energy release (differs from spherical) Black: >1000 Pa Grey: > 500 Pa E2E2 (1)(3)(2)(4) point source conical source (flight) conical (flight) + 3 point flares (fragmentation) ~light curve

12. Shock wave of Chelyabinsk meteoroid Time evolution: - outer shock wave - area of energy release Energy 520 кт, Energy deposition ~light curve

13. ~85 km S Shock wave of Chelyabinsk meteoroid

14. ~85 km S Shock wave of Chelyabinsk meteoroid

15. -solid orange circles - for reported damage -open black circles - for no damage; -solid red circles the most damaged villages in each district (as reported by officials) White - the fireball brightness on a linear scale. Contours : (from dark to light) 300 kt  p>1000 Pa, 520 kt  p>1000 Pa, 300 kt  p>500 Pa, 520 kt  p>500 Pa Map of glass damage on the ground The shape of damaged area – corresponds to energy deposition along extended part of trajectory Brown et al.(2013): P~2.6-3.8 kPa based on % of broken windows and glass pieces velocity Max fraction of injured people (0.16%): Korkino: 2-4 kPa Chelyabinsk: model ~2-4 kPa

16. Blast wave arrival times z 0 ~ 23 km Blast wave arrival times for given trajectory (V and inclination angle) are dependent on final altitude of energy release z 0 Blast is coming from the closest point of trajectory (in 3D) ~70 records in area 157x125 km In agreement with: Brown et al. 2013 - the source of shock in Chelyabinsk – at 23-30 km (ray approximation) Miller et al. 2013 – bottom wake boundary at 22 km (satellite image analysis) Only a negligible fraction of the initial kinetic energy (and mass) was probably deposited below 23 km.

17. Local shocks: -may be generated by energy release maxima - propagate inside ballistic cone - may reveal as separate peaks after main arrival Number of peaks, time delay dependent on - parameters of energy maxima - location of registration X=-16 km X=0 km schematic energy release Overpressure time dependence Need to be careful in attribution of local maxima on dE/dz –possible to add artificial or to lose real one due to sophisticated shocks interaction inside ballistic cone 3 peaks only 2 peaks  P time variation at different locations (3)

18. Pervomaysky Korkino Model (energy release ~light curve) X=20 Y~0 No direct agreement (different locations, rough grid, peculiarity of local shocks interaction etc), but ΔP has similar duration of variations in model/observations In both cases ( averaged observations and model ) number of arrivals varies with registration location X~0, Y~0 X~16,Y~7 X=-20 Y~0 Model and observed waveforms  t~2-10s  t~3-10s Observed (averaged, Δ~0.7 s) very diverse, vary with registration location rough numerical grid; cannot describe short time P variations

19. Korkino coal mine Sensors - triggering records - bandpass 4-100 Hz ( signals are essentially modified by geophons) Records - records starts – 03:21:59 GMT - duration – 23 s - one main arrival on all sensors 6 seismic sensors - borehole deepness – up to 14 m - vertical diversion - 288 m - covered area - 2.2*1.0 км 2 - different soil properties Bearing determination: - arrival time - in agreement with arrival model - from minimal distance to trajectory -source position at H~25-27 km (in agreement with trajectory) ~7 km to trajectory projection

20. Overpressure at Korkino N sensor А max (x), μm/s А max (y), μm/s А max (z), μm/s Vp, m/s measured Density kg/m 3  P (Pa) based on Z amplitude Maximal variation (z)  P (Pa) based on maximal variation 2116153167 179322006593201262 3540457571 10021800103011102002 44854112 232221005462201073 5230148523 228021002504 1060 5075 7176300359 1608210012127002364 8499252471 1706210016879303332  P average 1273 2518 σ 729 1494  P scatter: - the main spectrum of signal is probably below than sensors range (<4.5 Hz), that results in signal distortion - signal frequency is dependent on seismic velocity in 0-30 m soil layer (Langston, 2004) - coupling efficiency (acoustic-seismic) is not well known  P - in agreement with shockwave model results (2-4 kPa) Overpressure:  P ~ A z *ρ soil *Vp, normal and oblique wave incidence – close results Signal amplitudes and spectra are different on different sensors

21. Main signal Subsequent signals 4z 2z 5z There are two more sharp arrivals on 3 seismic records in Korkino (  t~12, 14 s) - could be produced by subsequent acoustic arrival as 1)waveforms/time delay and relation between different components are identical with main signal Seismograms, velocity of displacement Waveforms of signals at Korkino 6 sec18 sec Used filter 4-12Hz for all seismograms 2) sonic booms are present at acoustic record from close location (<1.3 km) with similar  t~12, 14 (but booms are more numerous) 3) bearing corresponds to arrival from H~29-34 km Other nature of these arrivals can not be excluded now, needs further investigation  P~100-500 Pa if considered these signals as acoustically produced acoustic

22. Light curve (and its modeling) provide an understanding how meteoroid energy was deposited Light curve of Chelyabinsk bolide: - by analysis of video observations of the fireball and the shadows (Borovicka et al., Brown et al., Popova et al., 2013) main difference – secondary maximum (camera automatic control) -similarity with other Satellite Network bolides (unfortunately only few curves were released) The energy deposition (and corresponding SW/damage) is essentially governed by fragmentation 6 june 2006 26 kt 40 kt Lines – from Borovicka et al. (2013) Pointed – from Popova et al. (2013) Chelyabinsk Manner in which energy is deposited SN bolides light curves

23. Meteoroid fragmentation Energy is deposited at 50-20 km altitude due to fragmentation. Complicated character of meteoroid disruption: - formation of decelerated debris cloud and independent fragments continued their flight with subsequent further disruption

24. Liquid – like (pancake)Progressive fragmentation Modeling of meteoroid fragmentation Meteoroid fragmentation: - formation of separated fragments - cloud of small fragments and vapor united by a common shock wave Both types are realized in real events: Benesov, Almahata Sitta, Tagish Lake, +Chelyabinsk Modeling of these processes provide independent estimate of energy deposition the amount material that goes into clouds and into separated fragments number distribution of fragments that are created and that survive 26 km 28 km

25. Hybrid model:  part of mass – independent fragments (~20t at H~27 km, could reach the ground)  part of mass - spreading debris clouds ( decelerated at 27-20 km; observed: 29-26 km)  f ragmentation occurred at loadings ~ P~0.3-10 MPa allows to reproduce the observed light/deceleration curves observed model M vapor ~76% M 0 ; M dust ~24% M 0 M meteorites ~0.03-0.06% M 0 All models agree with complicated character of fragmentation, which starts at ~50-45 km and ends at ~20-18 km (essential around 30-40 km) (Borovicka et al 2013, Brown et.al 2013, Avramenko et al. 2014 etc) Modeling efforts Lightcurve, model fit (dashed), mass passing given altitude (thin), normalised rate of energy deposition (low thin)

26. Chelyabinsk dust trail Other events: 3 September 2004 (Klekociuk et al., 2005) : M~650 – 1400 ton, M dust ~1100 t, μm-sized 4-m sized 2008 TC 3 : M dust ~25% M 0 (5%- recondensed) (Borovicka and Charvat, 2009) Detail of the train's thermal emission (5-6 s after formation) Electro-L, ~8 min after entry After 3 hours – at L~1000 km After 4-7 days – dust ring around pole (H~30-40km, 5 km thick, ~300 km wide; 0.9-0.05 μm) After 3 months – still existed Gorkavyi et al. 2013 Dust cloud – formed during fragmentation, at 80-20 km, more massive 40-25 km Our modeling suggests that a similar value applies to Chelyabinsk

27. Small meteoroids (<1-20 meters): complicated fragmentation, where fragments: - may form debris cloud, - may move as individual bodies, - decelerate before total evaporation - produce meteorites and dust deposition in the atmosphere Larger (30-300m) meteoroids (hydrodynamical modeling), their fragments -move as a cloud surrounded by a common shock, -decelerate later and have more chances to be totally evaporated Aerial bursts - "burning out" of comparatively large (D~ 100 m) bodies in the atmosphere (Wasson and Boslough, 2000) - the entire energy is released in the atmosphere - no observable crater is formed - affect the Earth’s surface (fires, shock waves) - typical example - Tunguska event Large meteoroids (>100-1000m): - do not decelerate in the atmosphere, - produce craters The boundaries between these regimes - on projectile composition, entry V and impact angle Fragmentation scenario

28. Dependent on projectile sizes/material and trajectory angles  (to horizon) ; note different vertical scale (Shuvalov and Trubetskaya, 2007); Violet ellipse - Tunguska body Solid fragments of comet D>100 m reach the ground at  ~90 0 ; 300-m asteroid could mainly burn in the atmosphere in 5 0 oblique impact The height of energy release may be essentially decreased (10-20 km) if internal friction effect is included (Shuvalov and Trubetskaya 2010) Asteroidal V~20km/s Cometary V~50 km/s Different styles of impact

29. Cosmic objects <100 m in size could result in meteors (no ground effects) -airbursts – surface aerial bursts in dependence on their properties/trajectory Goals: - quick rough evaluation of the impact consequences (levels of damage, area of the damage, etc) - to characterize average damage without details Approach: At large distances from the ground zero the spherical source provides a reasonable SW evaluation Restrictions: - there is no total analogy between point explosion - meteoroid entry - the shape of the region is determined by the dE/dz profile (i.e. by the details of the flight and disruption; the shape wouldn’t be circular unless α=90 0 ) What is needed: -to determine an effective explosion altitude - the altitude of energy equivalent point explosion Effective airburst altitude Method: two-stage model (Shuvalov et al. 2014) first stage - simulation of meteoroid motion taking into account its deformation, deceleration, disruption and evaporation (allows to determine energy release (Shuvalov and Artemieva 2002; Shuvalov and Trubeckaya 2007)) second stage – simulation of airblast propagation (determination of SW damaging effects) Both stages: SOVA code (Shuvalov 1999) Used: air EOS (Kuznetcov et al. 1965; Avilova et al. 1970); chondritic and cometary materials EOS (Kosarev 1999; Kosarev et al. 1996)

30. Relative density distribution along trajectory at different altitudes h D=40 m, V=18 km/s; chondritic material (2650 kg/m 3 ), α=90 0 Black – solid meteoroid material Stages of evolution body deformed, flattened ( H~20-25 km) and fragmented into nonuniform debris jet (H<15 km) debris jet evolution – the most energy release Effective airburst altitude: first stage Restriction: quasyliquid meteoroid (strength, separated fragments formation are not taken into account)

31. Main stages of evolution body deformed, flattened and fragmented into nonuniform debris jet explosive – type evaporation and vapor jet formation, its fast deceleration upward deceleration of hot vapor along the wake and plume formation (Shuvalov, Artemieva, 2007) Effective airburst altitude: first stage D=100 m; cometary; 45 0 ; V~ 50km/s

32. The relative density distribution ρ/ρ0(z) after the impact (time is counted after SW touching the surface; distances – in km) Effective airburst altitude: second stage Overpressure dependence on the surface after vertical impact Thick red – meteoroid impact simulation Thin blacks – point explosions at different altitudes H Outer boundaries - in agreement; peak values – may be underestimated D=40 m, asteroidal, ~3.4 Mt Relative density

33. Dimensionless effective altitude z/H dependence on ϑ Red points – asteroids; blue crosses – comets; Line – linear fit Effective airburst altitude Given impactor energy the quick evaluation of damage may be done assuming point explosion with the same energy at effective airburst altitude This altitude is dependent on meteoroid size D, meteoroid density and entry angle (there is no velocity dependence as the deceleration efficiency and increase of disrupted meteoroid cross-section are both dependent on entry V) Various impactor parameters: chondritic and cometary material, entry velocity, density, evaporation specific heat, opacities

34. Effective altitude Z dependence on meteoroid size for entry angles 15-90 degrees Red – asteroids; Blue – comets; For bodies < 10-30 m the uncertainty up to ~10 km (strength, fragmentation features etc) Effective airburst altitude

35. Collins et al. 2005: Earth Impact Effects calculator - stony meteoroids disrupted at loading ~0.2-0.6МPa (doesn’t contradict observational strength estimates at first breakup 0.1-1 МPа; Popova et al. 2011) - pancake model (Chyba et al. 1993) Comparison with our estimates: - altitude difference up to 5-7 km (the largest – for small entry angles ~5-15 0 ) -Underestimates overpressure for aerial bursts (Chelyabinsk case) Effective airburst altitude Effective airburst altitude dependence on D for various entry angles (15-90 0 ) Solid curves – our approximation Dashed - Collins et al. 2005 (3.3 g/m 3 ; 20 km/s) Our approach: -Precision of estimates - 2-3 km (random character of disruption) -Is applicable for D>10-30 m when strength and fragmentation features are not essential - for D~10-20 m the uncertainty in effective altitude may reach 10-15 km (Chelyabinsk, TC 3 2008 and other cases) Diameter, m Altitude, km

36. Tunguska event (30 June 1908) Energy, Mt Effective altitude, km Total damaged area 1700 km 2 Entry angle<45 0 (bolide or plume visibility in Preobrazhenka) Energy – 6.5-19 Mt Altitudes of bursts Z 6.5 – 10 km (based on fallen trees, Svetsov 2007) Narrow range of possible parameters: for 3300 kg/m 3 V<33 km/s, for V=30 km/s : 41°<α<45° V=12 km/s : 23°<α<45° for 1000 kg/m 3 V<18 km/s Contour: possible E and Z for Tunguska; Curves – corresponding possible V and α according Z(α) 3300 kg/m 3

37. The relative pressure P/P 0 (a,b) and heat fluxes J (c) versus distance R from ground zero for vertical impacts of asteroids 20 - 30 - 40 - 50 - 70 - 100 - 200 - 300 m correspondingly (different scale on (a) and (b)) Horizontal lines correspond to overpressure 1 kPa (а), 20 and 35 kPa (b), and flux 10 J/cm 2 (c) Given known damaging effects it is possible to map them for quick risk assesment Evaluation of damaging effects J, J/cm 2

38. Prototype of the information-analytical system on risk assessment list of near-Earth objects selected from the full NEO list based on chosen criterion Parameters of selected object If probability of collision is non-zero - its possible trajectory is determined: speed - time - the entry point with uncertainty (for a number of virtual objects)

39. Prototype of the information-analytical system on risk assessment Predicted overpressure zones for Chelyabinsk-like object taking into account the uncertainty of entry trajectory scale Parameters of impactor and trajectory Characteristics of damaged area damaging factor

40. Chelyabinsk event unique: large damage in the populated area (large size), huge amount of data; demonstrates that 20-m bodies are dangerous, provides a unique opportunity to calibrate models  Assumption that the energy release followed the meteor light curve satisfactory explained the butterfly-shape of the damaged area.  The SW characteristics may be described in the frame of the suggested hydrodynamical model (and simplified model for  t(z)), are in agreement with observational data (damage area, arrival times, overpressure level)  Main SW arrival is coming from the closest point of trajectory (in 3D), local shocks may be generated by energy release maxima (propagate inside ballistic cone, may reveal as separate peaks after main arrival, their number and time delays depend on parameters of maxima and location of registration) For quick rough evaluation of impact consequences for ~20-100 m bodies the point source provides a reasonable first approximation (due to similarity of SW at large distances from ground zero). Numerical simulations of impactor disruption/deceleration determine the effective height of the explosion, which is described by simple analytical formula A prototype of the information-analytical system on risk assessment and prevention of the consequences of cosmic impacts was created, which collects all possible consequences and demonstrates them visually on the geographical map (u sed simplified estimates should be refined) Concluding remarks