Terrestrial Planets

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Terrestrial Planets

• Lecture 15
• NATS102-13
• 13 October 2009

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Exam Results
Exam Results
A gt 65 B 45-65 C 35-45 D 25-35 E lt25
B
C
E
Mean 45 Median 43
Highest 89 Lowest 10
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Problems
Good News
Almost everyone understands why the Earth has
seasons

• Orbital velocity
• Why does the moon have phases?
• Retrograde motion
• Definition of the Equinox
• Orbital problems

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Advice

• Show your work. We cant give partial credit
  otherwise.
• Make sure that your work is legible.
• Check the units.
• Review lectures, come to class, pay attention.
• Pay attention to the big topics - Falling
  objects, Galileo and the phases of Venus,
  Erathosthenes and the size of the Earth,
  Discoveries with telescopes, Keplers third law,

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The moon goes through phases each month
because a) The distance between the Earth and
moon varies throughout the month. b) The shadow
of the Earth falls on different parts of the
moon. c) The orbit of the moon is tilted with
respect to the orbit of the Earth. d) The moon
moves along its orbit and we see different
amounts of its sunlit side.
Figure from Astronomy Today by Chaisson and
McMillan
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Jupiter orbits the Sun in a nearly circular orbit
with a semi-major axis of 5.2 AU. How fast is
Jupiter moving? Express your result in km/s to
two significant figures.
C 2?a
velocitydistance/time distance
circumferencetime period v 2?a/p p2 a3 a
5.2 AU p 11.86 years v 2?(5.2)/(11.86)
AU/year v 2.75 AU/yearv 2.75?1.5?1011/(11.86?
3.15?107)m/s v 1.3?104 m/s 13 km/s
a
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Please Think

• Retrograde motion occurs when
• The Earth changes the direction of its orbit.
• The moon changes the direction of its orbit.
• Mars changes the direction of its orbit.
• Mars appears to change the direction that it
  moves relative to the stars.

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Where was I last week?
41st annual meeting of the Division for Planetary
Sciences of the American Astronomical
Society Sunday October 4 to Friday October 9,
2009 El Conquistador Resort, Fajardo, Puerto
Rico, USA
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Results from the MeetingThe saga of Asteroid
2008 TC3
Meteorites are rocks that are believed to come
from outside of Earth - they come to Earth in a
meteor shower. There are many instances of
meteorites being found associated with the
observation of a shooting star. The parent body
of meteorites are believed to be asteroids that
collided with the Earth. 2008 TC3 is the first
asteroid detected in space that actually hit the
Earth. Astronomers photographed the asteroid in
space and predicted where it would hit the Earth.
The meteor shower was seen and meteors were
found on the ground.
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Asteroids
Main AsteroidBelt
Near EarthAsteroids
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News Flash Oct 6th, 2008
Looking for a little excitement tonight? An
asteroid between 1-5 meters (3-15 feet) was
discovered just hours ago at an Arizona
observatory, and might provide a spectacular
light show as it comes through Earth's
atmosphere. But don't be alarmed scientists
predict it will be harmless and burn up before it
reaches the ground. It is expected to be visible
over eastern Africa, at approximately 246 a.m.
Greenwich Mean Time (1046 p.m. Eastern time ).
There is no danger to people or property since
the asteroid will not reach the ground. It will
burn up in the upper atmosphere, well above
aircraft heights. The Universe Today
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U of A Catalina Sky Survey
Telescopes on Mount Lemon
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Discovery Photo
Wheres the Asteroid?
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Particulars

• Detected by Richard Kowalski about 20 hours
  before impact
• About 3-5 meters in size
• Entered atmosphere at 13 km/s (29,000 mph). This
  corresponds to an energy of 1 kiloton of TNT
• Disrupted near 25 miles altitude

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Image of the fireball
EUMETSAT (weather satellite) photo
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Seen from an airliner
This confirming report comes from Jacob Kuiper
ltmailtojacobkuiper at solcon.nlgt, General
Aviation meteorologist at the National Weather
Service in the Netherlands "Half an hour before
the predicted impact of asteroid 2008 TC3, I
informed an official of Air-France-KLM at
Amsterdam airport about the possibility that
crews of their airliners in the vicinity of
impact would have a chance to see a fireball.
And it was a success! I have received
confirmation that a KLM airliner, roughly 750
nautical miles southwest of the predicted
atmospheric impact position, has observed a short
flash just before the expected impact time 0246
UTC. Because of the distance it was not a very
large phenomenon, but still a confirmation that
some bright meteor has been seen in the
predicted direction.
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Go to website
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Predicted Track Impact Sudan
Remember the definition of UT?
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Contrails from the Meteor
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Meteorite Hunters (Students) in Sudan
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Guess which rock is the meteorite
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More Meteorites
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Trouble with the bus
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Some of the pieces were rather small
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9.2 Shaping Planetary Surfaces

• Our goals for learning
• What processes shape planetary surfaces?
• Why do the terrestrial planets have different
  geological histories?
• How do impact craters reveal a surfaces
  geological age?

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Terrestrial Planets

• Mercury
• Venus
• Earth Moon

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What processes shape planetary surfaces?
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Processes that Shape Surfaces

• Impact cratering
• Impacts by asteroids or comets
• Volcanism
• Eruption of molten rock onto surface
• Tectonics
• Disruption of a planets surface by internal
  stresses
• Erosion
• Surface changes made by wind, water, or ice

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Impact Cratering

• Most cratering happened soon after solar system
  formed
• Craters are about 10 times wider than object that
  made them
• Small craters greatly outnumber large ones

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Impact Craters
Meteor Crater (Arizona)
Tycho (Moon)
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Impact Craters on Mars
standard crater
impact into icy ground
eroded crater
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Volcanism

• Volcanism happens when molten rock (magma) finds
  a path through lithosphere to the surface
• Molten rock is called lava after it reaches the
  surface

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Lava and Volcanoes
Runny lava makes flat lava plains
Slightly thicker lava makes broad shield volcanoes
Thickest lava makes steep stratovolcanoes
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Outgassing

• Volcanism also releases gases from Earths
  interior into atmosphere

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Tectonics

• Convection of the mantle creates stresses in the
  crust called tectonic forces
• Compression forces make mountain ranges
• Valley can form where crust is pulled apart

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Plate Tectonics on Earth

• Earths continents slide around on separate
  plates of crust

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Erosion

• Erosion is a blanket term for weather-driven
  processes that break down or transport rock
• Processes that cause erosion include
• Glaciers
• Rivers
• Wind

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Erosion by Water

• Colorado River continues to carve Grand Canyon

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Erosion by Ice

• Glaciers carved the Yosemite Valley

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Erosion by Wind

• Wind wears away rock and builds up sand dunes

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Erosional Debris

• Erosion can create new features by depositing
  debris

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Why do the terrestrial planets have different
geological histories?
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Role of Planetary Size

• Smaller worlds cool off faster and harden earlier
• Larger worlds remain warm inside, promoting
  volcanism and tectonics
• Larger worlds also have more erosion because
  their gravity retains an atmosphere

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Role of Distance from Sun

• Planets close to Sun are too hot for rain, snow,
  ice and so have less erosion
• More difficult for hot planet to retain
  atmosphere
• Planets far from Sun are too cold for rain,
  limiting erosion
• Planets with liquid water have most erosion

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Role of Rotation

• Planets with slower rotation have less weather
  and less erosion and a weak magnetic field
• Planets with faster rotation have more weather
  and more erosion and a stronger magnetic field

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Thought Question

• How does the cooling of planets and potatoes
  vary with size?
• a) Larger makes it harder for heat from inside
  to escape
• b) Larger has a bigger ratio of volume (which
  needs to cool) to surface area (the surface is
  where cooling happens)
• c) Larger takes longer to cool
• d) All of the above

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Thought Question

• How does the cooling of planets and potatoes
  vary with size?
• a) Larger makes it harder for heat from inside
  to escape
• b) Larger has a bigger ratio of volume (which
  needs to cool) to surface area (the surface is
  where cooling happens)
• c) Larger takes longer to cool
• d) All of the above

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How do impact craters reveal a surfaces
geological age?
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History of Cratering

• Most cratering happened in first billion years
• A surface with many craters has not changed much
  in 3 billion years

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Cratering of Moon

• Some areas of Moon are more heavily cratered than
  others
• Younger regions were flooded by lava after most
  cratering

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Cratering of Moon
Cratering map of Moons entire surface
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9.3 Geology of the Moon and Mercury

• What geological processes shaped our Moon?
• What geological processes shaped Mercury?

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What geological processes shaped our Moon?
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Lunar Maria

• Smooth, dark lunar maria are less heavily
  cratered than lunar highlands
• Maria were made by flood of runny lava

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Formation of Lunar Maria
Early surface covered with craters
Cooled lava is smoother and darker than
surroundings
Large impact crater weakens crust
Heat build-up allows lava to well up to surface
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Tectonic Features

• Wrinkles arise from cooling and contraction of
  lava flood

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Geologically Dead

• Moon is considered geologically dead because
  geological processes have virtually stopped

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What geological processes shaped Mercury?
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Cratering of Mercury

• A mixture of heavily cratered and smooth regions
  like the Moon
• Smooth regions are likely ancient lava flows

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Cratering of Mercury
Region opposite Caloris Basin is jumbled from
seismic energy of impact
Caloris basin is largest impact crater on Mercury
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Tectonics on Mercury

• Long cliffs indicate that Mercury shrank early in
  its history

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What have we learned?

• What geological processes shaped our Moon?
• Early cratering still present
• Maria resulted from volcanism
• What geological processes shaped Mercury?
• Cratering and volcanism similar to Moon
• Tectonic features indicate early shrinkage

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9.4 Geology of Mars

• How did Martians invade popular culture?
• What are the major geological features of Mars?
• What geological evidence tells us that water once
  flowed on Mars?

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How did Martians invade popular culture?
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Canals on Mars

• Percival Lowell misinterpreted surface features
  seen in telescopic images of Mars

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What are the major geological features of Mars?
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Cratering on Mars

• Amount of cratering differs greatly across
  surface
• Many early craters have been erased

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Volcanism on Mars

• Mars has many large shield volcanoes
• Olympus Mons is largest volcano in solar system

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Tectonics on Mars

• System of valleys known as Valles Marineris
  thought to originate from tectonics

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What geological evidence tells us that water once
flowed on Mars?
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Dry Riverbeds?

• Close-up photos of Mars show what appear to be
  dried-up riverbeds

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Ancient Riverbeds
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Islands in the Stream
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Erosion of Craters

• Details of some craters suggest they were once
  filled with water

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Martian Rocks

• Mars rovers have found rocks that appear to have
  formed in water

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What have we learned?

• How did Martians invade popular culture?
• Surface features of Mars in early telescopic
  photos were misinterpreted as canals
• What are the major geological features of Mars?
• Differences in cratering across surface
• Giant shield volcanoes
• Evidence of tectonic activity

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What have we learned?

• What geological evidence tells us that water once
  flowed on Mars?
• Features that look like dry riverbeds
• Some craters appear to be eroded
• Rovers have found rocks that appear to have
  formed in water
• Gullies in crater walls may indicate recent water
  flows

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9.5 Geology of Venus

• Our goals for learning
• What are the major geological features of Venus?
• Does Venus have plate tectonics?

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What are the major geological features of Venus?
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Radar Mapping

• Thick atmosphere forces us to explore Venus
  surface through radar mapping

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Cratering on Venus

• Impact craters, but fewer than Moon, Mercury,
  Mars

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Volcanoes on Venus

• Many volcanoes, including both shield volcanoes
  and stratovolcanoes

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Tectonics on Venus

• Fractured and contorted surface indicates
  tectonic stresses

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Erosion on Venus

• Photos of rocks taken by lander show little
  erosion

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Does Venus have plate tectonics?

• Most of Earths major geological features can be
  attributed to plate tectonics, which gradually
  remakes Earths surface
• Venus does not appear to have plate tectonics,
  but entire surface seems to have been repaved
  750 million years ago

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What have we learned?

• What are the major geological features of Venus?
• Venus has cratering, volcanism, and tectonics but
  not much erosion
• Does Venus have plate tectonics?
• The lack of plate tectonics on Venus is a mystery

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9.6 The Unique Geology of Earth

• Our goals for learning
• How do we know Earths surface is in motion?
• How is Earths surface shaped by plate tectonics?
• Was Earths geology destined from birth?

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How do we know Earths surface is in motion?
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Continental Motion

• Motion of continents can be measured with GPS

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Continental Motion

• Idea of continental drift was inspired by
  puzzle-like fit of continents
• Mantle material erupts where seafloor spreads

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Seafloor Crust

• Thin seafloor crust differs from thick
  continental crust
• Dating of seafloor shows it is usually quite young

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How is Earths surface shaped by plate tectonics?
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Seafloor Recycling

• Seafloor is recycled through a process known as
  subduction

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Surface Features

• Major geological features of North America record
  history of plate tectonics

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Surface Features

• Himalayas are forming from a collision between
  plates

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Surface Features

• Red Sea is forming where plates are pulling apart

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Rifts, Faults, Earthquakes

• San Andreas fault in California is a plate
  boundary
• Motion of plates causes earthquakes

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Plate Motions

• Measurements of plate motions tell us past and
  future layout of continents

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Hot Spots

• Hawaiian islands have formed where plate is
  moving over volcanic hot spot

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Was Earths geology destined from birth?
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Earths Destiny

• Many of Earths features determined by size,
  rotation, and distance from Sun
• Reason for plate tectonics not yet clear

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What have we learned?

• How do we know that Earths surface is in motion?
• Measurements of plate motion confirm idea of
  continental drift
• How is Earths surface shaped by plate tectonics?
• Plate tectonics responsible for subduction,
  seafloor spreading, mountains, rifts, and
  earthquakes

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What have we learned?

• Was Earths geology destined from birth?
• Many of Earths features determined by size,
  distance from Sun, and rotation rate
• Reason for plate tectonics still a mystery