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

MORPHOLOGYof IMPACT CRATERS

Henrik Hargitaihargitai@emc.elte.hu

Origins• Lunar Craters

• Volcanic (17-19th century) (Galilei)• Impact (20th century) (Wegener, Gilbert)• Great Basins

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 energyEnergy 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

Formationstages

• Contact/• compression• Excavation• Modification

SimpleCrater•Small (3-10 km)•Bowl-shaped•Da apparent depth •Dt true depth

Fallout ejectaEjecta blanket

Breccia lens

Rim crest

Crater fill sediment

Complex craters• Elastic rebound• Central peak (structural uplift [SU])• Ring depression (flat floor/annular

basin)

rim Ejecta Terrace/slump

sedimentpeak

Melt sheet

brecciaShatter cones

Monomict Autochtonbreccia

Allochton Polimictbreccia

Flat floor crater

• „walled plains”• Sediment / • lava-filled

Dawes-typePlato, Moon

Central ring crater

• Complex crater with internal ring

• >4 km on EarthSchrödinger, Moon Lowell, Mars Barton, Venus

W Clearwater,Québec, Canada

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

Doublet craters

• Physical or „optical”• Source: Double asteroids

Toutatis Venus

Clearwater

Possible Optical

Catena (crater chain)

• Source: distrupted comets• (Shoemaker Levy 9) (impact to Jupiter, 1994)

Davy Catena

Ganymede

Mars: Volcanic origin

Crater cluster

• Multiple asteroid or• Synchronous impact of

• Exploded incoming body• In the atmosphere

Central pit/domecraters

• Pit: volatile rich material explodes / released (ice melted)

• Dome: Mars polar areas• Ice/snow deposits

Erosion:

• Buried / Ghost craters• Lava or sediment

Crater under ice polygons (Mars)

Rayed crater

• Ejecta jets• Fresh material (colour

difference)• Mars: above the dust

layer• Optical freshness:

1 Gy

Tycho, Moon

Unnamed, Mars

Petal Ejecta

• On Venus• P=90 atm, CO2

atmosphere• Extreme pressure• „supercritical state”• Fluidized atmosphere/rock interaction• With missing segment (at incoming

direction)

Lobate ejecta

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

Pedestal

Butterfly ejecta

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

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)

Secondaries

• Secondary impacts

• Often V shaped• Small craters on

Mars all secondaries?

Relaxed craters

• Ice in regolith• Softened terrain• „melted craters”• Freeze-thaw cycle

Enceladus

Mars

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

Cometary craters

P/Wild 2

Pit halo structures• Ejecta, Microgravity, homogenous material

Flat floor structures• No ejecta, steep slope: porous material

• Thank you• Henrik Hargitai

• hargitai@emc.elte.hu

Tempel 1 / Deep Impact