1. MORPHOLOGY of IMPACT CRATERS Henrik Hargitai hargitai@emc.elte.hu

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

3. Morphology depends: Impact energy E=1/2mv 2 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 (1/2mv 2 ) Temperature and pressure are also related to the potential energy (E p =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. Formation stages Contact/ compression Excavation Modification

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

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

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

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

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 ToutatisVenus Clearwater PossibleOptical

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

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

13. Central pit/dome craters 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 (colour difference) Mars: above the dust layer Optical freshness: 1 Gy Tycho, Moon Unnamed, Mars

16. Petal Ejecta On Venus P=90 atm, CO 2 atmosphere 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 P/Wild 2 Pit halo structures Ejecta, Microgravity, homogenous material Flat floor structures No ejecta, steep slope: porous material

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