The trajectory, structure and origin of The trajectory, structure and origin of

the Chelyabinsk asteroidal the Chelyabinsk asteroidal impactorimpactor

JiJiřříí BoroviBoroviččkakaAstronomical Institute, Academy of Sciences, Ondřejov, Czech Republic

HyMep, Erice, October 4, 2017

with the help of O. Popova (Moscow) and P. Brown (London, ON)

Feb 15, 2013, 3:20 UTFeb 15, 2013, 3:20 UT

�� Chelyabinsk and wide Chelyabinsk and wide surroundingssurroundings

�� Extremely bright Extremely bright superbolidesuperbolide

�� During local sunriseDuring local sunrise

�� Damaging blast waveDamaging blast wave

�� Massive dust trailMassive dust trail

Chelyabinsk cityChelyabinsk city�� More than million More than million

inhabitantsinhabitants�� Central Russia, south Central Russia, south

UralUral

http://города-россия.рф/

Damage by the blast waveDamage by the blast wave

�� Many windows Many windows brokenbroken

�� ~ 1600 injured ~ 1600 injured peoplepeople

�� Collapsed roof of Collapsed roof of a zinc planta zinc plant

Dust trail in the atmosphereDust trail in the atmosphere

Hole in ice, Hole in ice, ChChebarkulebarkul lakelake

�� Small meteorite fragments found Small meteorite fragments found on iceon ice

�� A 650 kg fragment recovered A 650 kg fragment recovered from the lake on October 16from the lake on October 16

�� 70 km 70 km W of W of ChelyChelyabinskabinsk

�� DiameterDiameter 8 m8 m�� Impact observed by Impact observed by

local fishermen and local fishermen and caught by a camera caught by a camera from distancefrom distance

MeteoritMeteoriteses under the snowunder the snow

�� TotallyTotally > 100 kg> 100 kg�� Many other meteorites Many other meteorites

found in spring, including found in spring, including a 4 kg piecea 4 kg piece

�� Ordinary chondrites, type Ordinary chondrites, type LL5LL5

�� South of ChelyabinskSouth of Chelyabinsk�� Thousands of mostly small Thousands of mostly small

meteorites, one big meteorites, one big (1,8 kg)(1,8 kg)

The importance of trajectory The importance of trajectory determinationdetermination

�� Inputs for modeling of the entryInputs for modeling of the entry

�� Heights of fragmentation (strength and structure Heights of fragmentation (strength and structure of the body)of the body)

�� Heights of energy deposition (damage Heights of energy deposition (damage assessment)assessment)

�� Location of meteoritesLocation of meteorites

�� PrePre--impact orbit (origin, search for preimpact orbit (origin, search for pre--discovery discovery images)images)

Available dataAvailable data

�� Videos (~1000), including Videos (~1000), including audio tracksaudio tracks

�� Seismic recordsSeismic records

�� Infrasonic records from Infrasonic records from around the worldaround the world

�� Satellite observationsSatellite observations•• US Government sensorsUS Government sensors

•• Meteorological satellitesMeteorological satellites

�� Recovered meteoritesRecovered meteorites

�� Damage on ground Damage on ground MSG2 satellite (EUMETSAT, CHMI)

See the video summary …

Stellar calibration of videosStellar calibration of videos

15 videos from 9 cities used15 videos from 9 cities used

Later extended to 29 videos

Trajectory computationTrajectory computation

�� Straight least Straight least squares method squares method ((BorovickaBorovicka 1990)1990)

�� Additional Additional corrections to corrections to account for account for EarthEarth’’s gravitys gravity

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15Time [s]

-5

-4

-3

-2

-1

0

1

2

3

4

5

Ver

tical

dev

iatio

n [k

m]

Measurementsvideo 1video 2video 14

Expected curvature

Note: Velocity (time) measurements neededto compute expected curvature

1850 bolide measurementson 15 videos

Trajectory and velocityTrajectory and velocity

Observed height span: 95.1 – 12.6 km

Initial velocity: 19.03 ± 0.13 km/s

Slope: 18.5° at the beginning17° at the end

Length of luminous trajectory: 272 km

Terminal velocity: 3.2 km/s

Bolide duration: 17 seconds

Data from Borovička et al. (2013). Popova et al. (2013) obtained similar values.

Fragmentation modelFragmentation model

�� Input dataInput data•• Light curveLight curve (total bolide brightness as a function (total bolide brightness as a function

of time/height)of time/height)

•• Times of arrivals of secondary Times of arrivals of secondary sonic boomssonic booms

•• DDecelerationeceleration toward the end of trajectorytoward the end of trajectory

�� ModelingModeling•• SemiSemi--empirical fragmentation modelempirical fragmentation model

•• Fitting the deceleration and major features of the Fitting the deceleration and major features of the light curvelight curve

Observed and modeled light curve Observed and modeled light curve (the brightest part)(the brightest part)

dust = sub kg fragments

Other models Other models

�� Hybrid model (Hybrid model (PopovaPopova et al. 2013)et al. 2013)

�� FragmentFragment--cloud model (Wheeler et al. 2017)cloud model (Wheeler et al. 2017)•• Both use combination of individual fragments and Both use combination of individual fragments and

debris clouds to explain the light curvedebris clouds to explain the light curve

�� Strength models (Robertson et al. 2017)Strength models (Robertson et al. 2017)•• No ablation, disruption depends on strength modelNo ablation, disruption depends on strength model

�� QuasiQuasi--liquid model (liquid model (ShuvalovShuvalov et al. 2017)et al. 2017)•• Single body with no strengthSingle body with no strength

observed

model

PopovaPopova et al. (2013)et al. (2013)

Lightcurve - black Model fits – red and blue

�� Part of mass Part of mass ––independent independent fragments fragments

�� Other part Other part ––spreading debris spreading debris clouds clouds

�� Fragmentation at Fragmentation at P ~ 0.3P ~ 0.3--10 10 MPaMPa

�� In total >96In total >96%% of of mass goes into mass goes into debris cloudsdebris clouds

Wheeler et al. (2017)Wheeler et al. (2017)

�� Three disruptions Three disruptions into four almost into four almost equal fragments equal fragments and a debris and a debris cloudcloud

�� Dust cloud forms Dust cloud forms 86% of mass at 86% of mass at each disruptioneach disruption

General model with limited number of free parameters

Robertson et al. (2017)Robertson et al. (2017)

�� Burst Burst altitude altitude depends depends on shear on shear strengthstrength

�� Strength Strength < 5 < 5 MPaMPa

ShuvalovShuvalov et al. (2017)et al. (2017)

�� HydrocodeHydrocode� No strength,

separated fragments formation not taken into account

Main featuresMain features

�� All models agree on ~95% loss of mass in All models agree on ~95% loss of mass in form of dust and small fragments at form of dust and small fragments at heights 40 heights 40 –– 30 km30 km

�� Numerous sonic booms suggest Numerous sonic booms suggest numerous individual fragmentation eventsnumerous individual fragmentation events

�� Extent of the dust trail shows that dust loss Extent of the dust trail shows that dust loss started already at high altitudesstarted already at high altitudes

Light curve and source heights Light curve and source heights of sonic boomsof sonic booms

60 55 50 45 40 35 30 25 20Height [km]

0

20

40

60

80

100M

esur

ed n

orm

aliz

ed s

igna

l Mesured signalBeloreck (bolide)Kurgan (bolide)Tyumen (bolide)Nizhny Tagil (illumination)

Break-up positions from sonic boomsMirnyi

0.7 MPa

2 MPa

4 MPa

5 MPa

10 MPa18 MPa

dynamic pressure ρv2:

Extent of the dust trailExtent of the dust trail

� starting at height ~70 km

� diameter 2–3 km between heights 60–25 km

� volume ~600 km3

No evidence for an early No evidence for an early fragmentationfragmentation

0 2 4 6 8 10 12 14Time [seconds after 3:20:20 UT]

-5

-10

-15

-20

-25

-30A

ppro

xim

ate

abso

lute

mag

nitu

de

h = 70 km

Fragmentation sequenceFragmentation sequence�� Intensive dust release (from nearIntensive dust release (from near--surface) started at surface) started at

height ~ 70 kmheight ~ 70 km�� First fragmentation at ~ 45 km at First fragmentation at ~ 45 km at P P ~ 0.5 ~ 0.5 MPaMPa (1% (1%

mass loss) mass loss) �� Large scale disruption (95% mass loss) at 39Large scale disruption (95% mass loss) at 39––30 km 30 km

height with height with PP = 1= 1––5 5 MPaMPa�� By 29 km object was 10By 29 km object was 10––20 boulders of sizes20 boulders of sizes 11––3 3 m m �� These boulders break again at 26These boulders break again at 26––22 km under 22 km under PP ~ ~

1010––18 18 MPaMPa�� Lateral fragment speeds ~400 Lateral fragment speeds ~400 m/sm/s

Normal tensile strength of meteorites is ~ 50 MPaFractures in the body decreased the bulk strength

Fragmentation and decelerationFragmentation and deceleration

Individually observed fragmentsIndividually observed fragments

Motion of the fragmentsMotion of the fragments

13.5 14 14.5 15 15.5 16 16.5 17 17.5 18Time [seconds after 3:20:20 UT]

12

14

16

18

20

22

24

26

28H

eigh

t [km

]HS3

HS2HS1

TE

M

F1

F12

F7

F2F3

F6F5 F4

F13

F14

F11

F16F15

450 kg*

0.5-30 kg*

0.2-5 kg*

* assuming spherical shape

hot spots

Detail Detail –– end of trajectoryend of trajectory

using wind from Verkhnee Dubrovo

A 24 kg meteorite recoveredA 24 kg meteorite recovered

Found 240 m from the predicted location of fragment F3

December 1, 2013

Detail Detail –– lake lake ChebarkulChebarkul

2 km

wind: F1 – V. Dubrovo, K – Kurgan, U – UKMO model, G – G2S model

Total energyTotal energy

�� Brown et al. (2013)Brown et al. (2013)• Seismic 430 kt TNT• Infrasound 600 • US government sensor 530• Video-derived light curve >470

�� PopovaPopova et al. (2013)et al. (2013)• Infrasound, damage area 570

1 kt TNT = 4,185 ×1012 J

Comparison with other airburstsComparison with other airbursts

30 30 ktktMarshall islands Marshall islands (1994)(1994)

50 50 ktktIndonesia (2009)Indonesia (2009)

500 500 ktktChelyabinsk Chelyabinsk (2013)(2013)

10 Mt10 MtTunguska (1908)Tunguska (1908)

EnergyEnergyBolideBolide

1515 ktktHiroshima bomb (1945)Hiroshima bomb (1945)

20 20 MtMtMt. St. Helen volcano Mt. St. Helen volcano (USA 1980)(USA 1980)

50 50 MtMtLargest thermonuclear Largest thermonuclear explosion (USSR 1961)explosion (USSR 1961)There was an unconfirmed ~1 Mt

bolide over Indian Ocean in 1963

~85 km S(from O. Popova)

Numerical model of shock wave and Numerical model of shock wave and trail evolutiontrail evolution

~85 km S(from O. Popova)

Map of glass damage with models of overpressure

(Popova et al. 2013)

7, 230 7, 230 buildings affected

Orbit was similar to that of asteroid Orbit was similar to that of asteroid 86039 (1999 NC43)86039 (1999 NC43)

(Borovička et al.2013)

Asteroid 86039 (1999 NC43)Asteroid 86039 (1999 NC43)�� Diameter 2.2 kmDiameter 2.2 km

�� Spectral type Q (ordinary Spectral type Q (ordinary chondritechondrite))

�� Rotation period 122.2 hours (tumbler)Rotation period 122.2 hours (tumbler)

�� There is only ~1:10,000 chance that the There is only ~1:10,000 chance that the proximity of Chelyabinsk orbit with an asteroid of proximity of Chelyabinsk orbit with an asteroid of this size is due purely to chance this size is due purely to chance

�� However, detailed spectral comparison does not However, detailed spectral comparison does not confirm genetic relation (Reddy et al. 2015)confirm genetic relation (Reddy et al. 2015)

Spectral comparisonSpectral comparison

�� Chelyabinsk Chelyabinsk meteorites meteorites –– LL typeLL type

�� 1999 NC43 1999 NC43 –– L typeL type

(Reddy et al. 2015)(Reddy et al. 2015)

SummarySummary�� ChelyaChelyabinskbinsk was extraordinary largewas extraordinary large: :

massmass 1122 000 t000 tonsons, , sizesize 1199 metmetersers

�� Relatively fragile body; disrupted at 30 km Relatively fragile body; disrupted at 30 km heightheight

�� Only small part of the original mass landed Only small part of the original mass landed as meteoritesas meteorites

�� Damage only from the blast waveDamage only from the blast wave. . If the If the body penetrated deeper intact, the blast body penetrated deeper intact, the blast wave would be strongerwave would be stronger

�� Potential riskPotential risk –– misidentification with misidentification with military attack military attack