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OBLIQUE IMPACT OBLIQUE IMPACT AND ITS EJECTA – AND ITS EJECTA –
NUMERICAL NUMERICAL MODELINGMODELING
Natasha Artemieva and Betty PierazzoNatasha Artemieva and Betty Pierazzo
Houston 2003Houston 2003
ContentContent
Oblique impact in nature and in Oblique impact in nature and in modelingmodeling
3D modeling – brief history3D modeling – brief history Hydrocodes in useHydrocodes in use Melt productionMelt production Fate of the projectileFate of the projectile Distal ejecta – tektites and martian Distal ejecta – tektites and martian
meteoritesmeteorites
Impact angleImpact angle
Vertical impact ( =90) - 0 Grazing impact ( = 0) - 0 Most probable angle =45
Probability of the impact within the angle (, +d): dP=2sin cos d
50% - (30 -60)7% - ( 0 -15)7% - (75 -90)
Elliptical craters on the Elliptical craters on the planetsplanets
~5-6% of the craters (Moon, Mars, Venus)Impact angle < 12
Asymmetrical ejectaAsymmetrical ejecta
Venus, Golubkina, 30 kmMagellan photo
Mars, small fresh cratersMars Global Surveyer
3D Hydrocodes versus 2D3D Hydrocodes versus 2D More complex? Or simpler?More complex? Or simpler? Time and computer capacity expensiveTime and computer capacity expensive Widely used in impact modeling:Widely used in impact modeling: CTHCTH – Sandia National Laboratories – Sandia National Laboratories SALE SALE – Los-Alamos National Laboratory – Los-Alamos National Laboratory SAGESAGE – Los-Alamos National Laboratory – Los-Alamos National Laboratory SOVA SOVA – Insitute for Dynamics of – Insitute for Dynamics of
Geospheres, RussiaGeospheres, Russia SPH SPH – various authors– various authors AUTODYN AUTODYN - commercial- commercial
Shoemaker-Levy 9 CometShoemaker-Levy 9 Comet
July 1994July 1994 Impact velocity – 60 Impact velocity – 60
km/skm/s Impact angle - 45Impact angle - 45 21 fragments21 fragments Size, density - unknownSize, density - unknown Observations – Observations –
telescopes, HST, Galileotelescopes, HST, Galileo Modeling – CTH, SOVA, Modeling – CTH, SOVA,
SPH et al.SPH et al.
3D modeling of fireball3D modeling of fireball
Crawford et al., 1995
Space Telescope Science Institute, 1994
Melt production – Melt production – comparison with geologycomparison with geology
From Pierazzo et al, 1997
Ries: real and model Ries: real and model stratigraphystratigraphy
quartz ite , 30% porosity
ca lc ite , no poros ity
quartz ite , 20% porosity
gran itic basem ent
a ) P re - im p ac t s tra tig rap h y b ) S im p lif ied S tra tig rap h y
Stoffler et al., 2002
Melt for the RiesMelt for the Ries
- 1 0 1 2 3 4 5
- 3
- 2
- 1
0
1
2
DE
PT
H, K
M
20 k m/s
- 1 0 1 2 3 4 5
- 3
- 2
- 1
0
1
2
1505 50
Shock modified molten partially vaporized
Stoffler et al., 2002
Is it useful to geologists?Is it useful to geologists?
Not all the melt remains within the Not all the melt remains within the cratercrater
What is the final state of the melt?What is the final state of the melt?
What is the final crater?What is the final crater?
More work is needed…..
Scaling for oblique Scaling for oblique impactimpact
Vtr = 0.28 pr/t Dpr2.25g-0.65V1.3sin1.3
Schmidt and Housen, 1987Gault and Wedekind, 1978Chapman and McKinnon, 1986
0 30 60 90im pact angle, degrees
1
1.5
2
2.5
3
Vtr
/Vtr
(Eq
. 5
)
Dpr ~ (sin)-0.55
Ivanov and Artemieva, 2002
Experiments and Experiments and modeling (DYNA) for modeling (DYNA) for
strength cratersstrength craters
increase of oblique impact cratering efficiency at higher increase of oblique impact cratering efficiency at higher velocities in experiments (Burchell and Mackay, 1998) and velocities in experiments (Burchell and Mackay, 1998) and modeling (Hayhurst et al., 1995)modeling (Hayhurst et al., 1995)
0 15 30 45 60 75 900
0.2
0.4
0.6
0.8
1
V /
V(9
0o
)
Al-->Al
16 km s-1
10 km s-1
6.5 km s-1
0 15 30 45 60 75 900
0.2
0.4
0.6
0.8
1
V /
V(9
0o
)
Fe-->Al
16 km s-1
10 km s-1
Natural impacts – high Natural impacts – high efficiencyefficiency
Laboratory – low efficiencyLaboratory – low efficiency
Distal ejectaDistal ejecta
TektitesTektites
Meteorites from other planetsMeteorites from other planets
Three stages for distal ejecta Three stages for distal ejecta evolutionevolution
Compression and ejection after Compression and ejection after impactimpact
disruption into particlesdisruption into particles
flight through atmosphere and final flight through atmosphere and final deposition (or escape)deposition (or escape)
Melt disruption into Melt disruption into particlesparticles
Pure melt ( 50 <P < 150 Pure melt ( 50 <P < 150 GPa): disruption by tension GPa): disruption by tension and instabilities. and instabilities.
Particle size is defined by balance of Particle size is defined by balance of surface tension and external forces.surface tension and external forces.
Particle size – cmParticle size – cm
Two-phase mixture Two-phase mixture
(P > 150 GPa): partial (P > 150 GPa): partial vaporization after vaporization after decompressiondecompression
Particle size is defined by amount of gas.Particle size is defined by amount of gas.
Particle size - Particle size - m – mm.m – mm.
Melosh and Vickery, 1991
Particles in flightParticles in flight
0 4 8 12 16 20Tim e after im pact, s
0
200
400
600
Mas
s of
par
ticle
s in
flig
ht, M
ton
tektites
m icrotektitesMelt + vapor - 700 MtEjecta - 540 Mt“Tektites” - 140 Mt“Mtektites” - 400 Mt
Trajectory in Trajectory in atmosphereatmosphere
0 100 200 300 400 500D istance from im pact, km
0
100
200
Alti
tude
, km
Pressure-temperature Pressure-temperature along trajectoryalong trajectory
5 10 15 20 25 30Tim e, s
1E -8
1E-7
1E-6
1E-5
1E-4
Dyn
amic
pre
ssur
e, G
Pa
5 10 15 20 25 30Tim e, s
0
1000
2000
3000
Tem
pera
ture
, K
Strewn field:Strewn field:Modeled: Real:
Deposited outside ejecta blanket – 15 MtGeological estomates – 5 Mt
0 100 200 300 400 500
D istance a long tra jectory, km
-200
-100
0
100
200
Dis
tanc
e ac
ross
traj
ecto
ry, k
m
Last minute resultsLast minute results
0 1 0 0 0 2 0 0 0 3 0 0 0 4 0 0 0
-2 0 0 0
-1 0 0 0
0
1 0 0 0
2 0 0 0
0
2 0
4 0
6 0
8 0
1 0 0
5 0 0
0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0
-2 0 0
-1 0 0
0
1 0 0
2 0 0
Initial stage Initial stage
High-velocity unmelted material is ejected at the stage of compression t ~ Dpr/V
Where are they from?Where are they from?
Excavation depth: 0.1 Dpr
Distance from impact point: 1.5 - 2 Dpr
0 1 2 3 4D I ST AN CE FRO M I M PACT PO I NT , KM
-2
-1
0
1
2
ALT
ITU
DE,
KM
57148
79
144
54
1.8
3013
9
0 . 0 0 . 5 1 . 0 1 . 5 2 . 0
X / D
Y / D
Ejection velocity vs. shockEjection velocity vs. shock
0 20 40 60Maximum pressure, GPa
4
6
8
10
Eje
cti
on
ve
loc
ity
, k
m/s
0 .131
0.006
No SNC without shock compression!
Deceleration by Deceleration by atmopshereatmopshere
Only particles with
d >20 cm may escape Mars !
Independent confirmation – 80Kr (Eugster et al., 2002)
0 10 20 30TIME AFTER IMPACT, S
1E-4
1E-3
1E-2
1E-1
1E+02
0.6
0.2
0.1
Impact conditions:Impact conditions:
Impact velocity : 10 km/sImpact velocity : 10 km/s Impact angle : 45 °Impact angle : 45 ° Asteroid diameter : 200 mAsteroid diameter : 200 m Final crater : 1.5 - 3 km Final crater : 1.5 - 3 km Maximum particle’s size -1mMaximum particle’s size -1m
Conclusions:Conclusions:
3D modeling is becoming possible 3D modeling is becoming possible thanks to computer improvementsthanks to computer improvements
We need 3D for:We need 3D for: scaling of impact eventsscaling of impact events melt production estimatesmelt production estimates investigation of projectile fateinvestigation of projectile fate vapor plume rising in vapor plume rising in
atmosphereatmosphere distal ejecta descriptiondistal ejecta description
Problems:Problems:
Computer expensiveComputer expensive
Spatial resolution limitationsSpatial resolution limitations
More physics is neededMore physics is needed
EOSEOS
Connection with Connection with observations:observations:
Melt and its final distributionMelt and its final distribution
Shock effects in SNC meteoritesShock effects in SNC meteorites
Tektites strewn fieldTektites strewn field