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)

Earth cratersEarth craters

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

Melt productionMelt production

From Pierazzo and Melosh, 2000

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

Projectile fateProjectile fate

From Pierazzo and Melosh 2000

Distal ejectaDistal ejecta

TektitesTektites

Meteorites from other planetsMeteorites from other planets

SNC size and shapeSNC size and shape

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

Particles in post impact Particles in post impact flowflow

ug

ug

ug

u

DRAG

GRAVITY

First 2 s (trajectory First 2 s (trajectory plane)plane)

Moldavites – first 20 sMoldavites – first 20 s

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

Connection with Connection with experiments:experiments:

??