Meteoroid fragmentation
in the Martian atmosphere
Olga Popova
Institute for Dynamics of Geospheres, Moscow, Russia
MIIGAiK, Moscow, 5-6 July 2012
An expanding class of meteorites
Due to:
- the rapid proliferation of video
recording devices
- the slower expansion of meteor
tracking networks
The last years have marked
an increase in the numbers
of meteorite recoveries, in
which accurate tracking
data reveal
 trajectories,
 orbit information
 details of the multiple
fragmentation
events
Thirteen cases were analyzed (Popova et al.,2011), all are stone meteorites;
sufficient data are believed to exist for recent Buzzard Coulee (H4, 2008), Košice (H5, 2010), Mason
Gully(2010) but detail data are still absent.
For the first time, this permits comparison of a substantial number of these
cases, where fragmentation behavior allows to infer mechanical properties,
such as strength, and investigate the bulk strength of meteoroids ⁄ small
asteroids as a function of mineralogical type and the size/mass.
Determining the fragmentation strength
It is usually assumed that the
meteoroid
disruption begins when the aerodynamic
pressure in the vicinity of a stagnation point
becomes equal to some constant describing
the strength σ of meteoroid material.
There are different approaches to the choice of
characteristic strength σ (compressive,
tensile, or shear) in the breakup criterion by
different authors (see Svetsov et al. 1995 for some
air flow,
ram pressure
Sresses in
meteoroid
rV2
discussion).
We will not consider here the stresses in the
meteoroid and mechanism of meteoroid
failure.
During the atmospheric loading, the internal stresses in the meteoroid are proportional
to the ram pressure (Fadeenko 1967; Tsvetkov and Skripnik 1991), and so we will consider the
stagnation pressure at breakup as the breakup criterion and measure of meteoroid
strength in the disruption.
The fragmentation strength of a meteoroid
- the loading ram pressure, which caused the fragmentation: σ = p = r V2
r, V - the atmospheric density and the fireball velocity at the fragmentation height H
To determine the fragmentation heights and strengths from fireball data – few
methods
To determine the fragmentation from fireball data
Geometric – fragments tracking on several subsequent images of fireball in
flight and the fragmentation heights H are determined by geometrically
intersecting trajectories
Příbram, Lost City, Innisfree, Peekskill, Moravka,Grimsby (Ceplecha 1961; McCrosky
et al. 1971; Halliday et al. 1981; Brown et al. 1994;Borovicka and Kalenda 2003; Brown et al.2010)
Bolide Moravka
(M~1.5t, H~30 km, 30 pieces),
Borovicka and Kalenda 2003
Dynamic - after a sudden mass loss, the deceleration increases.
(This can be revealed by fitting the fireball dynamics (Ceplecha et al. 1993))
Lost City, Moravka, Villalbeto de la Pena, Neuschwanstein, Bunburra Rockhole
(Ceplecha 1996; Borovicka and Kalenda 2003; Llorca et al. 2005;Spurny et al.2006, 2010)
To determine the fragmentation from fireball data
Photometric - the fragmentation events demonstrate themselves on the light curve.
The fireball flares are caused by the release of large amount of dust which is radiated
out quickly or a large number of macroscopic fragments is formed.
Tagish Lake bolide; Brown et al. 2002
fragmentation
Light curves of satellite observed bolides is possible to explain
only taking into account fragmentation (Nemtchinov et al., 1997)
intensity
The position of the flares was used to determine
altitude of fragmention and meteoroid strength in
many cases
Lost City, Tagish Lake, Park Forest, Villalbeto de la
Pena, Almahata Sitta, Jesenice, Grimsby (Brown et
time, s
al., 2002,2004,2010;Trigo-Rodríguez et al. 2005;Jenniskens et
al. 2009; Spurny et al.2010)
Model - a search of best fit both to light curve and trajectory data (many papers).
Method Ceplecha and ReVelle (2005) may be used for the cases with high precision observational data
To determine the fragmentation from fireball data
Analysis
of
acoustic/seismic
signals
-the fragmentation events are point
sources of sonic waves (ReVelle 2004;
Vitim bolide
Amplitude, relative units
September 24,
2002
T1s=16:51:20
ReVelle et al., 2004; Brown et al., 2002;
Edwards et al., 2006; Borovička and Kalenda
2003; and others)
T1a=16:56:29
Time, s
-allow to determine altitude of
fragmentation, released energy,
etc. Moravka, Villalbeto de la
Pena, Jesenice, Grimsby (Borovicka
T2s=16:53:03
T2a=17:07:19
and Kalenda 2003; Llorka et al. 2005; Spurny
et al.2010; Brown et al.2010)
All methods to determine
fragmentation have some restrictions:
T3s=16:52:37
T3a=17:04:04
Times of arrival: seismic signals ( T1s, T2s, T3s ) ;
infrasound signals ( T1a, T2a, T3a ). Seismic signal
arrived first (r1=142 km; r2=357 km; r3=276 km)
low resolution of images,
too small separation of fragments to
be detected,
 absence of flares at high altitudes,
 high precision data are needed for
model, etc.
High altitude fragmentation
The most difficult cases of fragmentation to reveal - the break-ups of
massive meteoroids at high altitudes:
- the low atmospheric density and still relatively large meteoroid mass even after
fragmentation leads to no measurable deceleration.
- if only small number of macroscopic fragments are produced, no meteor flare is
observed.
- the geometric separation of massive fragments is also minimal under low pressures at
high altitudes.
The fact that the fragmentation occurred becomes evident only at lower
altitudes (h<50 km), when the dynamic mass computed from the
deceleration appears to be much lower than the total meteoroid mass
determined from other methods.
To determine the high-altitude fragmentation the light data should to be
analysed together with dynamic ones
Benešov(Borovička et al. 1998) ; Morávka (Borovička and Kalenda 2003)
The fragmentation height can’t be determined.
The limiting case that the meteoroid entered the atmosphere as a swarm of
separated bodies cannot be even excluded.
Comments on meteoroid mass estimates
Dynamic mass - found based on
the
deceleration.
The
most
elaborated method fragmentation approach.
the
gross
Mass estimates by different methods for the cases
under consideration
‘Radiation’ mass - found from
light energy or intensity data. Few
estimates may be listed if different
luminous efficiency values were used or
the bolide was observed in different
passbands.
Mass - derived from infrasonic
and seismic signals. Mass range
is derived due to existence of several
methods of signal interpretation.
Initial mass - estimated based on
cosmogenic
nuclides
production rate, cosmic-ray
tracks analyses and noble
gases concentration.
Different
entry
models
(using
various
assumptions
concerning
luminous
efficiencies,
ablation
coefficients, presence of fragmentation,
its treating, material properties ) were
applied to the cases.
Mass estimates show large scattering due to
presence of a number of open questions in
methods.
If the mass estimates agrees with the
precision of about two times - these
estimates are quit reasonable
Observed strength for 13 well documented events
More often the strength
increases from the first
breakup to the following
this relationship does not
exactly follow a power law
(dashed lines)
~0.03 – 10 MPa
for M~ 10 - 5  104 kg
no obvious dependence of
meteoroid strength on mass
some later breakups occur
at lower loading pressure
than the earlier ones of the
same body
Most of the meteoroids causing terrestrial fireballs are very weak when they hit the top of
atmosphere. The cause may be that most meteoroids (even at meter scale) may be
highly fractured by previous collisions, or even rubble pile structures
Popova et al., 2011
Extended data on observed strength
13 bolides with detail data
17 fragmenting Prairie
Network fireballs
(Ceplecha et al. 1993),
-13 European Network bolides
-5 Satellite Network bolides;
Note:
Carancas meteorite
(M~1-4 t at impact, M~1.5-10 t at entry)
seems survived at 12-40 MPa
(Borovicka and Spurny, 2008;
Kenkmann et al.2009)
-meteoroids over a wide mass range fragment during entry under
similar low pressures, do not show expected trend
-data bias? influence of collisional history in space? internal friction
between formed fragment?
Popova et al, 2011
Sampled meteoroid properties
Fraction per 1 km/s
13 meteorite falls with detail data:
9 ordinary chondrites,
3 achondrites and 1 carbonaceous
chondrite.
Bulk densities : 1.64-3.59 g/cm3,
Microporosities : from 0 to ~40%
Entry velocity: 12.4 – 22.5 km/s
Fireball brightness: -9.3 -22magnitudes.
Initial masses: 22 - 70,000 kg
Their orbits suggest origins in various
parts of the main belt of asteroids.
In all cases, the fragmentation
proceeded in several steps.
Corresponding entry velocities on
Mars:
6.6 – 16.6 km/s
Frequency of the impact velocity for Earth and Mars
(Adolfsson et al. 1996)
( Ivanov 2008)
Constructed using orbits of observed planetary crossers listed
in the permanently updated catalog of small body orbits
astorb.dat
First breakup
In most cases, the first breakup on
occurred under the dynamic pressure
lower than 1 MPa,
Earth: H~70-40 km
It had the form of either
the separation of relatively small
fragment(s) from the main body
(Přibram, Innisfree, Park Forest),
 loosing about half of the mass
(Lost City),
 severe disruption of the body
creating fragments an order of
magnitude smaller than the original
mass (Peekskill, Moravka).
Altitudes of first breakup on Earth and Mars
Mars: H~46 - 2.7 km
Even in the cases when fragmentation <1 MPa was not observed (Neuschwanstein, Villalbeto
de la Peña) - may be because of paucity of data and not because of a real lack of produced
small pieces.
If absence of this breakup – real, no fragmentation in the Martian atmosphere
Fragmentation altitudes
Earth:
the maximum encountered loading pressure
5-10 MPa.
Fragmentation:
down to 19 km height in 3-5 main steps.
Mars:
Mainly in 1-2 main steps, down to the
planet surface
Fragmentation altitudes on Earth and
Mars
10 meteoroids from our 13 cases would
fragment in the case of Martian entry
(78%)
Size of corresponding craters on Mars
Fragmentation :
– appearance of crater clusters
-decrease of main fragment crater size
in 1.1 – 4 times
Crater sizes on Mars
(scaling laws for rocky and porous targets
suggested by Ivanov 2008 were used)
Similar meteoroids will form
3-80 m single craters on Mars
(in absence of fragmentation)
Best observational values of mass at breakup used
are not very precise
Examples of Small Martian clusters
•involve craters with diameter D~10 m spread over area roughly 100-300 m
across
•these clusters are consistent with weak meteoroids breaking up in the current
Martian atmosphere (Popova et al., 2003)
MGS MOC M09-02052
200 m
Arabia
3230W 120N
MGS/MOC M19-00278
200 m
MGS/MOC M02-0763
200 m
Newton
1580N 450S
NE wall Bakhuysen Crater
3430W 230S
MGS images in this presentation:
NASA, JPL, Malin Space Science Systems
Size of corresponding craters on Mars
Fragmentation :
– appearance of crater clusters
-decrease of main fragment crater size
In 10 cases masses after breakups on
in 1.1 – 4 times
Earth are estimated
In 8 cases similar meteoroids will
fragment on Mars
In 7 cases mass losses in the Martian
breakups will exceed 30%
Very rough upper estimate:
- up to 70% of similar impacts
(Dcrater~3-50 m) may be clusters
Daubar et al.(2010), Ivanov et al.(2010)
About 50-66% of fresh impacts are
clustered
Details of breakups are still poorly known – many uncertainties in cratering prediction
Moravka (06 May 2000) on Earth
M~ 1500
500 kg, V~22.5 km/s
6 fragments H5-6 chondrite
(0.09-0.33 kg)
M~1.4 kg (~0.1% M0) (predicted
M~100 kg~7% M0) (Borovička et al.,
2003)
Progressive fragmentation at 36-29 km,
possible disruption >46 km
Fragmentation: 43-30 km
~50-100 fragments in 0.09-0.31 kg;
M~20 - 30 kg; N~400-700 along 10-20 km
In dependence on assumed mass distribution at
breakup
I, W/sr
along 10 km strewn field
Modeling: progressive fragmentation
Strength scaling law (with random deviations)
8x109
Number
of fragments
4x109
Two fragments
0x100
Light curve fitting:
many small fragments formed,
probably another mass distribution at breakup;
does not suggest large amount of dust formed
2.4
2.8
3.2
t,s
3.6
4
Moravka-like meteoroid on Mars
One of the possible strewn field,
Number, size, location of craters are
dependent on assumed breakup details (SFD,
strength of fragments etc)
Much more material reach the ground.
Earth observations demonstrated:
different fragmentation scenarios occur
during the passage of meteoroids 0.1-10
m through the atmosphere.
There is a number of events, which
deposited essential fraction of their
masses as dust in the atmosphere (Tagish
Lake, Almahata Sitta etc)
Dust cloud of 2008 TC3 (Almahata Sitta meteorite)
Dust cloud illuminated by Sun
Dust clouds
observed in infrared chanels of Meteosat satellite
(Borovicka and Charvat 2009)
the brightest pixel at 35.7  0.7 km = dust cloud;
very roughly : if size ~ 1 m, mass~10 t
another dust cloud at 42 – 45 km : very roughly:
size ~ 1 m; mass~3 t
And 53 km???
3:38.8 UT
Borovicka and Charvat 2009:
•
•
•
Modeling – probably 30% of mass
is going into dust (~25 t) (should be taken into account
, impossible to reproduce light curve without…(Popova
2010).
Similar situation occurred for Tagish Lake meteoroid,
Hot silicate micron smoke
which would form similar dust cloud in Martian
(recondensed) ...  5%
conditions.
Warm -sized dust (decelerated)
Would any specific signatures appear on strewn field?
32
…  20%
Meteorites …  1%
Fractions of initial mass, which are converted into the
dust and/or meteorites is poorly estimated
Recovered meteorites mass on Earth
Number of meteorite falls with
tracking data on atmospheric
passage
(13 cases)
The relation of the recovered mass to the initial mass estimate
The fraction of recovered
masses - about 0.1-3 %
mainly.
The recovered mass smaller than estimated total
fallen mass due to
incomplete finding.
(Popova et al., 2011)
The highest fraction – for two smallest and slowest meteorites
(~10%, Lost City and Innisfree)
The smallest fraction <10-4 - Tagish Lake and Almahata Sitta meteorites
(largest fragment ~only about 10-5 of its initial mass)
due to specific composition and/or structure ?
(porosity 40 and 15-20%, inhomogenity and fragility )
If mrecoverd /M 0 ~ 1-5%, probably there are no large dust deposition (progressive fragmentation)
Concluding remarks
The measured low strength of Earth meteoroids suggest easy breakup in
Mars atmosphere for many meteoroids (but not strong, coherent stone or
iron meteoroids).
Up to 70% of similar impacts (Dcrater~3-50 m) may be clusters
Different fragmentation scenarios occur during the passage of meteoroids
0.1-10 m through the atmosphere, a number of events may deposit
essential fraction of their masses as dust in the atmosphere
Observational data are still incomplete to make definite conclusion, what
fraction of incoming bodies is fragile enough to deposit this dust and how
it is related with their structure/composition etc.
But even bodies, which deposited much of mass as a dust/vapor, are able
to produce meteorites on the Earth and craters on Mars. The total picture
of fragmented-body motion is comparatively complicated.
Better statistics is needed to estimate parameters of incoming cosmic
material and to predict its behavior in the atmosphere.
Fragmentation models
Liquid – like (pancake)
a swarm of small bodies, which
continues their flight as a
single mass with increasing
pancake-like cross-section
(Grigorjan (1979), Zahnle (1992),
Chyba et al (1993), Hills and Goda
(1993))
Progressive fragmentation
number of fragments,
which continue their flight
independently (Levin 1956, 1961;
Baldwin and Sheaffer 1971 and many others),
taking into account the lateral
spreading of fragments due to
fragments bow shock interaction
(Passey& Melosh (1980));
Both models were successfully used
to describe a limited number of
meteoroids passages
Ablation - included into standard equations (heat transfer coefficient, specific heat)
Liquid like models
are applicable for large impactors,
which are destroyed so intensively that
fragments couldn’t be separated (>~4-10 m in
size)
(Svetsov et al., 1995; Bland and Artemieva 2006: estimates are
parameters dependent),
say nothing about fragments size
But its modifications provide reasonable
energy release (similar to progressive
fragmentation models)
May be suitable for catastrophic disruption,
when huge number of fragments is formed
were used to explain light curves of meter in
Detailed study in the frame of
model of separated fragments (Artemieva,
Shuvalov 2002; Bland Artemieva 2006) – one of
progressive fragmentation type models
V~18 km/s; M>few kg
Iron and stones
for stones 0~4 107dyn/cm2
Strength scaling law
 = s (ms / m)
(, m – the strength and mass of
the larger body; s , ms – those of tested specimen);
small deviations are allowed ~10%
Mfall/M~0.05-0.1 for M~100 kg-1000 t stones
Larger for irons (0.05-0.5)
No fragmentation for M<50 kg
Result are dependent on assumed strength and
fragment distribution at breakup
Fragmentation has no influence on entry of
body larger 10 km (tflight<tfragmentation)
Hybrid model
Shape of light pulse varies from one numerical run to another
in every breakup some part of mass
formed spreading cloud of vapor
and dust
ΣN~103-
in every breakup only few fragments (2-3 in average) are
formed, some part of mass (~30% in average) formed
spreading dust cloud (black curves)
ΣMfall ~1-2 t; Mdust~20-25 t,
ΣN~103;
η ~ 4-5%; Er~0.07-0.08 kt
ΣMfall ~6-14 t;
105;
η ~ 3-5%; Er~0.06-0.08 kt
fragment
dust are
formed
(blue)
Essential
of mass
be
converted
into
dust inshould be e
M
~15-20
t, M
t should
Indust
order
tofraction
get
enough
long
lightonecurve
– and
variation
ofthe
strength
vapor~60
Mfall~ 5-15 kg; N=1; η ~ 5-6%; Er~0.08breakups.
0.09
kt is smaller about 100-400
Light curve may be fitted if fallen
mass
Examples of partings observed in large chondrites collected
on strewn fields
Al Huqf 011
SaU 238
Sayh al Uhaymir 272
Jiddat al Harasis (JaH) 275
a) Cut and polished
slab. A dominant set
of parallel, 2–4 cm
spaced shock veins
runs from top left to
bottom
right,
crosscut the stone
(20 cm). A second,
closer spaced, but
less pronounced set
of shock veins is
intersecting the first
at
high
angle.
Irregular
fissures
stained with metal
are well visible on
the right.
b) Chicken-wire network of shock veins, fluidized metal is common in the veins. c) Cut
slab, note that the widely open cracks are not, or only as closed fissures extending to
the surface of the stone. d) Slickensides. (e) Failure of the drill core due to shear
stress from the rotating drill occurred only along the shock vein discontinuities (25 cm
long JaH 073) .
Meteorite sample strengths
 MPa
The strength data
1000
-large scatter
(even for different samples of the same
meteorite, Tsarev for example).
100
The lowest strength
-the sample of Elenovka
L5 chondrite, very friable sample
Tsarev
10
Elenovka
- Compressional
These data are too scarce
- Tensile
to make any conclusions
1
about correlation of the
LL3
L5
L6
H3
H5
H6,
C
mesostrength and meteorite type
siderite
or shock stage.
Source: Migdisova and Zaslavskaya (1984); Chen et al. (1996);
Medvedev et al. (1985); Tsvetkov and Skripnik (1991); Svetsov et
al. (1995); Baldwin and Sheaffer (1971).
Should be noted that some carbonaceous chondrites are much
weaker and more crumbly than Kainsaz and Allende shown on
figure.
Extended data on observed strength
13 bolides with detail data
17 fragmenting Prairie
Network fireballs
(Ceplecha et al. 1993),
-13 European Network bolides
-5 Satellite Network bolides;
Note:
Carancas meteorite
(M~1-4 t at impact, M~1.5-10 t at entry)
seems survived at 12-40 MPa
(Borovicka and Spurny, 2008;
Kenkmann et al.2009)
-meteoroids over a wide mass range fragment during entry under
similar low pressures, do not show expected trend
-data bias? influence of collisional history in space? internal friction
between formed fragment?
Popova et al, 2011
Mars
Modeling
In Arabia, MGS MOC M09-02052
On channel wall in
Bakhuysen crater, M02-0763
MGS
images
in
this
presentation: NASA, JPL, Malin
Popova et al., 2007
200 m
V~10 km/s, D~1-3 m;
~0.25; different s
apparent strength
 ~ 1-10 bar
Concluding remarks
In all available cases the first disruption observed in the high atmosphere
occurred when the pressure and stress on the incoming body were
much less than the strength of the rocks collected on the ground.
We conclude that meter-scale interplanetary meteoroids, as found in
space, are typically highly fractured, presumably as a result of asteroid
collisional history, and can break up under stresses of a few MPa.
Weakness of some carbonaceous objects may result from very porous
primordial accretional structures, more than fractures.
These conclusions have implications for future asteroid missions, sample
extraction, and asteroid hazard mitigation.
Acknowledgments
We thank the International Space Science Institute of Bern, Switzerland, for sponsoring team
meetings that permitted us to collaborate on this research.