Solar System Planets: The Earth Moon

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Solar System Planets The Earth Moon

• Moon
• - Atmosphere
• - Surface/Geological Features/Moon Rocks
• - Interior
• - Origin
• II. Mercury
• - Basic Facts
• - Exploration
• - Cratering

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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

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Lunar Geological Features

• Craters
• 30,000 visible with small telescopes from Earth
• millions visible from lunar orbiting satellites
• origin interplanetary debris
• sizes largest 100s km
• across a result of fast
• moving impact rocks
• of only a few kms across!
• large craters often
• produce central peak
• craters

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

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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

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Cratering Age of Moons 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)
• Earths surface only a few
• 100 Myrs old (geological activity has re-surfaced
  planet)
• highlands have many more craters maria have
  fewer
• craters ? highlands older

The smaller the planet, the less internal
heat (geology) it will have less
geological activity on surface
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A Brief History of Lunar Exploration

• 1959 Soviet Lunas 1, 2, 3 orbited around Moon
• 1960s 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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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
Neil Armstrong Buzz Aldrin 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 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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Touchdown of Moon astronauts near the coast of
Hawaii on July 26th 1969
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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

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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

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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

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Moonquakes Studying the Moons Interior

• 3000 quakes/year
• much lower intensity
• than Earth 0.5-1.5 Richter
• indicate that Moons
• interior is more rigid than
• Earths (some plasticity)

Seismometer placed on Moon by lunar astronauts
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Moons 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
• - core is now solid, so no current is generated

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Color-coded images illustrate surface geography

• Clementine data
• blue lowland marias
• red - highlands

• Galileo data flyby in 1989
• blue lowland marias
• 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

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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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