1 / 43

OBLIQUE IMPACT AND ITS EJECTA – NUMERICAL MODELING

OBLIQUE IMPACT AND ITS EJECTA – NUMERICAL MODELING. Natasha Artemieva and Betty Pierazzo Houston 2003. Content. Oblique impact in nature and in modeling 3D modeling – brief history Hydrocodes in use Melt production Fate of the projectile Distal ejecta – tektites and martian meteorites.

melvin-taylor
Download Presentation

OBLIQUE IMPACT AND ITS EJECTA – NUMERICAL MODELING

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

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

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

  3. Impact angle Probability of the impact within the angle (, +d): dP=2sin cos d 50% - (30 -60) 7% - ( 0 -15) 7% - (75 -90) Vertical impact ( =90) - 0 Grazing impact ( = 0) - 0 Most probable angle =45

  4. Earth craters

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

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

  7. 3D Hydrocodes versus 2D • More complex? Or simpler? • Time and computer capacity expensive • Widely used in impact modeling: CTH – Sandia National Laboratories SALE – Los-Alamos National Laboratory SAGE – Los-Alamos National Laboratory SOVA – Insitute for Dynamics of Geospheres, Russia SPH – various authors AUTODYN - commercial

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

  9. 3D modeling of fireball Space Telescope Science Institute, 1994 Crawford et al., 1995

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

  11. Melt production From Pierazzo and Melosh, 2000

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

  13. Melt for the Ries 5 50 150 Shock modified molten partially vaporized Stoffler et al., 2002

  14. Is it useful to geologists? • Not all the melt remains within the crater • What is the final state of the melt? • What is the final crater? More work is needed…..

  15. Scaling for oblique impact Vtr = 0.28 pr/t Dpr2.25g-0.65V1.3sin1.3 Schmidt and Housen, 1987 Gault and Wedekind, 1978 Chapman and McKinnon, 1986 Dpr ~ (sin)-0.55 Ivanov and Artemieva, 2002

  16. 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)

  17. Natural impacts – high efficiencyLaboratory – low efficiency

  18. Projectile fate From Pierazzo and Melosh 2000

  19. Distal ejecta • Tektites • Meteorites from other planets

  20. SNC size and shape

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

  22. Melt disruption into particles • 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 – cm • Two-phase mixture (P > 150 GPa): partial vaporization after decompression Particle size is defined by amount of gas. Particle size - m – mm. Melosh and Vickery, 1991

  23. Particles in flight Melt + vapor - 700 Mt Ejecta - 540 Mt “Tektites” - 140 Mt “Mtektites” - 400 Mt

  24. Particles in post impact flow u ug DRAG ug ug GRAVITY

  25. First 2 s (trajectory plane)

  26. Moldavites – first 20 s

  27. Trajectory in atmosphere

  28. Pressure-temperature along trajectory

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

  30. Last minute results

  31. Initial stage High-velocity unmelted material is ejected at the stage of compression t ~ Dpr/V

  32. Where are they from? Excavation depth: 0.1 Dpr Distance from impact point: 1.5 - 2 Dpr

  33. Ejection velocity vs. shock No SNC without shock compression!

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

  35. Impact conditions: • Impact velocity : 10 km/s • Impact angle : 45 ° • Asteroid diameter : 200 m • Final crater : 1.5 - 3 km • Maximum particle’s size -1m

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

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

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

  39. Connection with experiments: ?

More Related