Download Mercury

Lecture 23
Movie Night 2
Monday, April 19
SW119 from 7:00~9:30
How do surface building processes
apply to the Terrestrial Planets?
Vulcanism
Impact cratering
Erosion
Tectonics
erosion
cratering
vulcanism
tectonics
Small rocky planets

Cold, solid interiors

Tectonic & volcanic
activity only
during
first billion years



Many ancient craters

No erosion
Little outgassing
Atmospheres lost
due to weak gravity
(Moon, Mercury)
Mercury
Geologically dead
Vulcanism when young (small lava plains, smaller crater
density than lunar highlands)
Days / Nights last 3 months – very hot / cold
Mercury
Tectonics when young
Very high cliffs extending
for hundreds of
kilometers, formed as
folds as planet cooled
and contracted
Moon
Highlands (light colored areas):
heavily cratered
about four billion years old
Mare
Dark colored areas:
giant impact basins
flooded with lava
lightly cratered
about 3.2-3.9 billion
years old (younger than
highlands)
(Earth, Venus)
Large rocky planets






Warm, convecting interiors
Ongoing tectonic & volcanic activity
Most ancient craters erased
Considerable outgassing
Atmospheres retained
Erosion exists
Venus
Fully cloud covered
– surface not visible
Surface features
on Venus have
been investigated
using radar from
orbiting
spacecraft
young surface
mostly gentle rolling plains.
evidence of volcanism.
Erosion
&
tectonics
few impact craters
tectonic activity
(folded grooves shown here)
Mars
Marsrovers.jpl.nasa.gov
erosion
cratering
vulcanism
tectonics
fewer craters in
northern hemisphere
heavily cratered southern
hemisphere
giant volcanoes
Olympus Mons
dry stream beds, once had running water
Considerable evidence of
water flows – younger terrain
heavily cratered southern hemisphere
Older terrain
Tectonics & erosion
Erosion around edge of
Olympus Mons
Conclusion:
part of surface young, part old
Summary: Surface Properties
Cratered terrain ubiquitous in the solar system
cratering due to planetesimals left over from
formation of solar system
smallest planets (Moon, Mercury) heavily
cratered
middle sized planet (Mars) has both heavily
cratered and also relatively uncratered regions
and extinct volcanos
largest planets (Venus, Earth) have few craters
and active volcanos
Why?
More impact craters implies an older
surface
Rate of cratering declined rapidly after
planet formation
Many craters remain where there is no
tectonic or volcanic activity
Why do some planets have old
surfaces and some young surfaces?
The level of
tectonic and volcanic activity
Thickness of lithosphere controls extent
of volcanic activity.
Thin lithosphere -> hot rocks from interior
break through surface
Thick lithosphere -> hot rocks from
interior can't break through surface.