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MORPHOLOGY of IMPACT CRATERS

MORPHOLOGY of IMPACT CRATERS. Henrik Hargitai hargitai@emc.elte.hu. Lunar Craters Volcanic (17-19th century) (Galilei) Impact (20th century) (Wegener, Gilbert) Great Basins . Origins. Morphology depends:. Impact energy E=1/2mv 2

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MORPHOLOGY of IMPACT CRATERS

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  1. MORPHOLOGYof IMPACT CRATERS Henrik Hargitai hargitai@emc.elte.hu

  2. Lunar Craters Volcanic (17-19th century) (Galilei) Impact (20th century) (Wegener, Gilbert) Great Basins Origins

  3. Morphology depends: • Impact energy • E=1/2mv2 Original impacting body usually evaporated during a hypervelocity impact event Crater is formed by shock wave from the released energy Energy of shock wave depends on kinetic energy (1/2mv2) Temperature and pressure are also related to the potential energy (Ep=mgh) Data for Mars: g=3.97, h[eight of the impacting body] v[elocity of impctor] asteroid: ~7 km/s, cometary body: ~42 km/s

  4. Formationstages • Contact/ • compression • Excavation • Modification

  5. SimpleCrater • Small (3-10 km) • Bowl-shaped • Da apparent depth • Dt true depth Fallout ejecta Rim crest Ejecta blanket Crater fill sediment Breccia lens

  6. Complex craters • Elastic rebound • Central peak (structural uplift [SU]) • Ring depression (flat floor/annular basin) rim Terrace/slump Ejecta peak sediment Melt sheet Allochton Polimict breccia Monomict Autochton breccia breccia Shatter cones

  7. Flat floor crater • „walled plains” • Sediment / • lava-filled Plato, Moon Dawes-type

  8. Central ring crater • Complex crater with internal ring • >4 km on Earth W Clearwater, Québec, Canada Barton, Venus Lowell, Mars Schrödinger, Moon

  9. Giant Multiringed Basins • Impact-related inner, • Tectonics related outer rings • Lava-fill possible • Valhalla-type • 20+ rings • Young elastic thin crust • Global effects Mare Orientale, Moon Valhalla, Callisto

  10. Doublet craters • Physical or „optical” • Source: Double asteroids Clearwater Toutatis Venus Possible Optical

  11. Catena (crater chain) • Source: distrupted comets • (Shoemaker Levy 9) (impact to Jupiter, 1994) Ganymede Davy Catena Mars: Volcanic origin

  12. Crater cluster • Multiple asteroid or • Synchronous impact of • Exploded incoming body • In the atmosphere

  13. Central pit/domecraters • Pit: volatile rich material explodes / released (ice melted) • Dome: Mars polar areas • Ice/snow deposits

  14. Erosion: • Buried / Ghost craters • Lava or sediment Crater under ice polygons (Mars)

  15. Rayed crater • Ejecta jets • Fresh material (colourdifference) • Mars: above the dust layer • Optical freshness:1 Gy Tycho, Moon Unnamed, Mars

  16. Petal Ejecta • On Venus • P=90 atm, CO2atmosphere • Extreme pressure • „supercritical state” • Fluidized atmosphere/rock interaction • With missing segment (at incoming direction)

  17. Lobate ejecta • Single Lobe Ejecta • Double Lobe Ejecta • Rampart • Regolith Ice Layers • Fluidized ejecta • Eroded: pedestal • Also: Pancake craters Pedestal

  18. Butterfly ejecta • Observed on Mars • „Grazing impact” • <5° impact angle • Also: Oval craters: • Rio Cuarto, Argentine • Mars

  19. Impact with no crater • Splotche (Dark spot) • Atmospheric explosion • Air Blast /Shock Wave • 1908 Tunguzka event • comet explosion at 8 km? • Penetration Crater: • Just a pit (not hypervelocity impact)

  20. Secondaries • Secondary impacts • Often V shaped • Small craters on Mars all secondaries?

  21. Relaxed craters • Ice in regolith • Softened terrain • „melted craters” • Freeze-thaw cycle Enceladus Mars

  22. Paimpsest • On Icy moons • Albedo difference • Relaxed (no topography) • Early age: viscous relaxation • Bright material from underneath • Remnant topography: Penepalimpsest (crust not viscous) • Geographic term: Facula

  23. Cometary craters • Pit halo structures • Ejecta, Microgravity, homogenous material • Flat floor structures • No ejecta, steep slope: porous material P/Wild 2

  24. Thank you • Henrik Hargitai • hargitai@emc.elte.hu Tempel 1 / Deep Impact

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