Download Cratering

Solar System Planets: The Earth + Moon
I. Moon
- Atmosphere
- Surface/Geological Features/Moon Rocks
- Interior
- Origin
II. Mercury
- Basic Facts
- Exploration
- Cratering
13 Oct 2003
Solar System - Dr. C.C. Lang
1
The Moon has no atmosphere
• allows us to see the surface with fine detail
• escape speed is too low on the Moon
- all gas molecules can escape!
• no atmospheric pressure means that water
can not exist in liquid form
- only in solid or vapor
• temperature variations – extreme!
- day T = 403 K = 266 F
- night T = 93 K = -292 F
- day/night are each 2 weeks long!
• no weathering of the surface by water, storm
• no protection from high energy solar
particles,
cosmic rays
13 Oct 2003
Solar System - Dr. C.C. Lang
2
Lunar Geological Features
1.Craters
•
•
•
~30,000 visible with small telescopes from Earth
millions visible from lunar orbiting satellites
origin: interplanetary debris
• sizes: largest 100’s km
across a result of fast
moving impact rocks
of only a few km’s across!
• large craters often
produce “central peak”
craters
13 Oct 2003
Solar System - Dr. C.C. Lang
Clavius Crater
diameter = 232 km
depth of 16,000 feet
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Lunar Geological Features
2. Lunar “Maria” - dark, smooth regions
• first thought to actually be wet areas (before we knew Moon had no atmosphere)
• now believed to be smoother, younger (fewer craters) surfaces
• idea is that impacts created large basin and then lava flowed over surface
• relatively ‘low’ compared to highlands on moon; 2-5 km below other parts
• rough mountain ranges surrounding ‘maria’ suggest large impact originally
• evidence for ‘flows’ (lava?) along the smooth maria
13 Oct 2003
Solar System - Dr. C.C. Lang
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Lunar Geological Features
3. Lunar Highlands
• most of moon (85%) is actually covered with lighter, higher land: Highlands
• predominantly on the side of the Moon facing away from Earth
• roughly cratered, but no smooth lava flow ‘maria’ regions
• crust must be thicker in the highland areas
13 Oct 2003
Solar System - Dr. C.C. Lang
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Cratering: Age of Moon’s Surface
• can use cratering patterns to
determine AGE of surface
• no atmosphere to protect
bombardment; no erosion by
wind/water  OLD surface
(as old as ~3 billion years)
The smaller the planet,
the less internal heat
(geology) it will
have; less geological
activity on surface
• Earth’s surface only a few
100 Myrs old (geological
activity has re-surfaced planet)
• highlands have many more
craters; maria have fewer
craters
 highlands ‘older’
13 Oct 2003
Solar System - Dr. C.C. Lang
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A Brief History of Lunar Exploration
• 1959: Soviet Lunas 1, 2, 3 orbited around Moon
• 1960’s: US Ranger
- flyby mission
- first space pictures
- many TV cameras
• 1966-67: Lunar Orbiter
- 5 orbiting spacecraft
- full coverage of pictures
• 1966-68: Lunar Surveyor
- surveying for landing sites
- testing the “soil” (sink?)
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Solar System - Dr. C.C. Lang
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Highlights from Apollo 11 mission
launch: July 16th 1969
arrival at Moon: July 20th 1969
first humans to land on the Moon
Command Module (CM):
“Columbia”
13 Oct 2003
Neil Armstrong
“Buzz” Aldrin
Solar System - Dr.
C.C. Lang
Michael
Collins
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On July 20, 1969, after a four day trip, the Apollo astronauts arrived
at the Moon. This photo of Earthrise over the lunar horizon is one of
the most famous images returned from the space program, although
13 Oct 2003
Solar System
- Dr. C.C.
Lang
even the astronauts themselves
cannot
remember
who actually took it.
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First steps on the Moon
• July 20th 1969
- Neil Armstrong
- “Buzz” Aldrin
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Solar System - Dr. C.C. Lang
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Touchdown of Moon astronauts near the coast of Hawaii on July 26th 1969
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Solar System - Dr. C.C. Lang
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Lunar Exploration: Apollo Missions
• Apollo 1-10: pre-landing missions (Apollo 1 module fire killed 3 astronauts
while being tested)
• Apollo 11-17 landed (except Apollo 13, which had an explosion and returned
to Earth) 12 different astronauts walked on the Moon during 1969-1972
• Principal Scientific results of the Apollo missions:
1. The Moon is ancient and still preserves an early history (the first billion
years) that must be common to all terrestrial planets.
2. The youngest Moon rocks are virtually as old as the oldest Earth rocks. The
earliest processes and events that probably affected both planetary bodies can
now only be found on the Moon.
3. Early in its history, the Moon was melted to great depths to form a "magma
ocean." The lunar highlands contain the remnants of early, low density rocks
that floated to the surface of the magma ocean.
4. The Moon is not a primordial object; it is an evolved terrestrial planet with
internal zoning similar to that of Earth.
5. The Moon is lifeless; it contains no living organisms, fossils, or native organic
compounds
13 Oct 2003
Solar System - Dr. C.C. Lang
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Recent Lunar Exploration
• 1994: Clementine
- UV, IR, visible cameras
- possible water ice at poles
- radio waves reflected off ice
• 1998: Lunar Prospector
- also found evidence for ice
- crashed near pole in 1999
• Currently: Smart 1 Probe
- European satellite
- ion propulsion (several months!)
- will search for water
at poles
13 Oct 2003
Solar System - Dr. C.C. Lang
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Moon Rocks: Sampling the Surface of the Moon
• surface material: “regolith” –
pulverized by constant impacts
• ~2500 samples brought back
by astronauts; ~850 lbs total!!
• all rocks are IGNEOUS (i.e.,
from molten processes)
• totally dry rocks (no water)
• all rocks older than 3 Byr
13 Oct 2003
Solar System - Dr. C.C. Lang
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Moonquakes: Studying the Moon’s Interior
• ~ 3000 quakes/year
• much lower intensity
than Earth: 0.5-1.5 Richter
• indicate that Moon’s
interior is more rigid than
Earth’s (some ‘plasticity’)
Seismometer placed
on Moon
by lunar astronauts
Solar System
- Dr. C.C. Lang
13 Oct 2003
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Moon’s interior structure
crust is thicker on
non-Earth facing side
• iron-rich core like Earth
• asthenosphere layer: somewhat pliable “plastic” layer
• solid layer just below surface – no plate tectonics
• smaller planet than Earth – less internal energy, less geological activity!
• moon probably had a weak magnetic field early in history
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Solarso
System
- Dr. C.C.isLang
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- core is now solid,
no current
generated
Color-coded images illustrate surface geography
Clementine data
Galileo data – flyby in 1989
• blue – lowland marias
• blue – lowland marias
13 Oct 2003 • red - highlands
Solar System - Dr. C.C. Lang • red - highlands
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Theories for Origin of Moon
• Fission: originally part of Earth but torn free
– Problem: would have fallen back or been flung into space,
not into orbit.
– Fails to explain why lunar chemistry differs from Earth's
• Co-Creation: formed in its present orbit
– can not explain why lunar chemistry differs from Earth's
• Capture: formed as a separate planet but captured by
Earth
– Conditions for successful capture very stringent
• Impact: formed from Mega-Impact of Mars-sized planet
– Computer modeling suggests SS forms 100 or so small
planets, then collide to make larger objects
– can explain differences in chemistry:
– impact occurred after chemical differentiation in Earth; therefore,
not as much iron was part of the Moon
– high temperatures during impact would have vaporized the
volatile and water vapor in rocks
– Currently favored model
13 Oct 2003
Solar System - Dr. C.C. Lang
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Computer Simulation of Formation of Moon
• Moon may have
formed by a
Mars-sized object
impact on Earth
• Some of the material
does not fall back
onto the Earth, but
forms a satellite
of Earth
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Solar System - Dr. C.C. Lang
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