Surfaces of the terrestrial planets

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Surfaces of the terrestrial planets
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Processes affecting planetary surfaces
Impact cratering craters build up slowly on
surface over time the older the surface, the
more craters it has this is used to measure
the age of planetary surfaces Tectonics faults
cut crust and pre-existing features tectonic
processes can destroy old features tectonism
can create a younger surface Volcanism builds
mountains flood lavas cover or fill in older
features volcanism can create a new, younger
surface Erosion, mass wasting modifies features
on the surface
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Age of planetary crusts (surfaces)
Primary crust created when planet was forming
made of minerals which floated on magma ocean -
lunar highlands Secondary crust created by
mantle melting and volcanism made of basaltic
rock - lunar mare basalts, crust of Mercury
Tertiary crust created by recycling and
reworking of secondary crust made of basalt or
more evolved rock - continents of Earth,
highlands of Venus
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Determining the age of planetary surfaces and
features
Absolute age of surface crater counts - number
of craters on surface radiometric dating of
rock samples (Earth, Moon, Mars) Relative ages
of surface features cross-cutting
relations older features are cut by younger
features (example faults cutting an old
volcano) superposition younger features are
superimposed on older features (example lava
flows filling in an old crater)
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Impact features on planetary surfaces
Double-ring impact basin on Mercury
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Impact craters on the lunar farside (large crater
is 60 km across)
Central peak
Slumping around walls
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Danilova crater on Venus
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Crater cluster impactor broke into four pieces
before hitting surface
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Splosh craters on Mars Impacts onto a wet
surface?
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Relative dating Superposition and cross-cutting
relations
Fault scarps on Mercury are younger than the
craters they cut across
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Half crater on Venus, partly destroyed by more
recent tectonic activity
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Younger volcanic flows filling older impact
basins on Earths moon (blue color)
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Recent slump and debris flow modifying an old
crater on Mars
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Absolute dating Crater counts
Craters accumulate over time on a planets
surface The more craters, the older the
surface is. Smaller craters accumulate more
rapidly than large ones. Each planet has its
own crater curve
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Meteorite impact rate over time Calibrated for
Earth-Moon system
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Old crater surfaces eventually become saturated.
A saturated surface is one that has so many
craters that any new impact will destroy some old
craters. Even with new impacts, there will be
no net increase in crater count.
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Cater counts can be different for different parts
of an objects surface
The darker regions on Ganymedes surface have
more craters (and more large craters) than the
light areas. This means the darker areas are
older. The lighter patches are regions of
younger surfaces.
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Circles show craters on Mars gt 100 km in diameter
Clearly some parts of Mars surface are older
than others
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Very large impacts are rare and mostly date from
the early solar system
If the impact forming crater Herschel had been
any larger, it would probably have destroyed
Mimas
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Accretion is still occurring During meteor
showers, small impacts are sometimes visible on
the dark portions of the Moon.
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The use of relative dating (superposition) and
absolute dating (crater counts) has told
planetary scientists much about the other worlds
in our solar system.