OBLIQUE IMPACT AND ITS EJECTA – NUMERICAL MODELING Natasha Artemieva and Betty Pierazzo Houston 2003

Content Oblique impact in nature and in modeling Oblique impact in nature and in modeling 3D modeling – brief history 3D modeling – brief history Hydrocodes in use Hydrocodes in use Melt production Melt production Fate of the projectile Fate of the projectile Distal ejecta – tektites and martian meteorites Distal ejecta – tektites and martian meteorites

Impact 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 craters

Elliptical craters on the planets ~5-6% of the craters (Moon, Mars, Venus) Impact angle < 12 

Asymmetrical ejecta Venus, Golubkina, 30 km Magellan photo Mars, small fresh craters Mars Global Surveyer

3D Hydrocodes versus 2D More complex? Or simpler? More complex? Or simpler? Time and computer capacity expensive Time and computer capacity expensive Widely used in impact modeling: Widely used in impact modeling: CTH – Sandia National Laboratories CTH – Sandia National Laboratories SALE – Los-Alamos National Laboratory SALE – Los-Alamos National Laboratory SAGE – Los-Alamos National Laboratory SAGE – Los-Alamos National Laboratory SOVA – Insitute for Dynamics of Geospheres, Russia SOVA – Insitute for Dynamics of Geospheres, Russia SPH – various authors SPH – various authors AUTODYN - commercial AUTODYN - commercial

Shoemaker-Levy 9 Comet July 1994 July 1994 Impact velocity – 60 km/s Impact velocity – 60 km/s Impact angle - 45  Impact angle - 45  21 fragments 21 fragments Size, density - unknown Size, density - unknown Observations – telescopes, HST, Galileo Observations – telescopes, HST, Galileo Modeling – CTH, SOVA, SPH et al. Modeling – CTH, SOVA, SPH et al.

3D modeling of fireball Crawford et al., 1995 Space Telescope Science Institute, 1994

Melt production – comparison with geology From Pierazzo et al, 1997

Melt production From Pierazzo and Melosh, 2000

Ries: real and model stratigraphy Stoffler et al., 2002

Melt for the Ries Shock modified molten partially vaporized Stoffler et al., 2002

Is it useful to geologists? Not all the melt remains within the crater Not all the melt remains within the crater 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 impact V tr = 0.28  pr /  t D pr 2.25 g V 1.3 sin 1.3  Schmidt and Housen, 1987 Gault and Wedekind, 1978 Chapman and McKinnon, 1986 D pr ~ (sin  ) Ivanov and Artemieva, 2002

Experiments and modeling (DYNA) for strength craters increase of oblique impact cratering efficiency at higher velocities in experiments (Burchell and Mackay, 1998) and modeling (Hayhurst et al., 1995)

Natural impacts – high efficiency Laboratory – low efficiency

Projectile fate From Pierazzo and Melosh 2000

Distal ejecta Tektites Tektites Meteorites from other planets Meteorites from other planets

SNC size and shape

Three stages for distal ejecta evolution Compression and ejection after impact Compression and ejection after impact disruption into particles disruption into particles flight through atmosphere and final deposition (or escape) flight through atmosphere and final deposition (or escape)

Melt disruption into particles Pure melt ( 50 <P < 150 GPa): disruption by tension and instabilities. Pure melt ( 50 <P < 150 GPa): disruption by tension and instabilities. Particle size is defined by balance of surface tension and external forces. Particle size is defined by balance of surface tension and external forces. Particle size – cm Particle size – cm Two-phase mixture Two-phase mixture (P > 150 GPa): partial vaporization after decompression (P > 150 GPa): partial vaporization after decompression Particle size is defined by amount of gas. Particle size is defined by amount of gas. Particle size -  m – mm. Particle size -  m – mm. Melosh and Vickery, 1991

Particles in flight Melt + vapor Mt Ejecta Mt “Tektites” Mt “Mtektites” Mt

Particles in post impact flow ugug ugug ugug u DRAG GRAVITY

First 2 s (trajectory plane)

Moldavites – first 20 s

Trajectory in atmosphere

Pressure-temperature along trajectory

Strewn field: Modeled: Real: Deposited outside ejecta blanket – 15 Mt Geological estomates – 5 Mt

Last minute results

Initial stage High-velocity unmelted material is ejected at the stage of compression t ~ D pr /V

Where are they from? Excavation depth: 0.1 D pr Distance from impact point: D pr

Ejection velocity vs. shock No SNC without shock compression!

Deceleration by atmopshere Only particles with d >20 cm may escape Mars ! Independent confirmation – 80 Kr (Eugster et al., 2002)

Impact conditions: Impact velocity : 10 km/s Impact velocity : 10 km/s Impact angle : 45 ° Impact angle : 45 ° Asteroid diameter : 200 m Asteroid diameter : 200 m Final crater : km Final crater : km Maximum particle’s size -1m Maximum particle’s size -1m

Conclusions: 3D modeling is becoming possible thanks to computer improvements 3D modeling is becoming possible thanks to computer improvements We need 3D for: We need 3D for: scaling of impact events scaling of impact events melt production estimates melt production estimates investigation of projectile fate investigation of projectile fate vapor plume rising in atmosphere vapor plume rising in atmosphere distal ejecta description distal ejecta description

Problems: Computer expensive Computer expensive Spatial resolution limitations Spatial resolution limitations More physics is needed More physics is needed EOS EOS

Connection with observations: Melt and its final distribution Melt and its final distribution Shock effects in SNC meteorites Shock effects in SNC meteorites Tektites strewn field Tektites strewn field

Connection with experiments: ?