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Earth Science 101
The
Solar System
Chapter 23
Instructor : Pete Kozich
Overview of the solar system
Solar system includes
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Sun
Eight planets and their satellites (moons)
Asteroids
Comets
Meteoroids
The solar system
Figure 22.1
Overview of the solar system
A planet’s orbit lies in an orbital plane
• Similar to a flat sheet of paper or a disc
• The orbital planes of the planets are inclined
• Planes of seven planets lie within 4 degrees of the
Sun's equator
• Mercury's is inclined 7 degrees
• Pluto's is inclined 17 degrees
Overview of the solar system
Two groups of planets occur in the solar
system
• Terrestrial (Earth-like) planets, the 4 inner planets
• Mercury, Venus, Earth, and Mars
• Small, dense, and rocky
• Low escape velocities (Earth is 7 miles/second or
25,200 mph)
• Rockets have to reach this to escape Earth’s gravitational pull
Overview of the solar system
Two groups of planets occur in the solar
system
• Jovian (Jupiter-like) planets or the gas giants
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Jupiter, Saturn, Uranus, and Neptune
Large, low density, and gaseous
Massive (Jupiter is 317 times more massive than Earth)
Thick atmospheres composed of hydrogen and helium
(Jupiter and Saturn) and methane and ammonia (Uranus
and Neptune)
• High escape velocities (14-40 miles/second or 50,400144,000 mph)
• Pluto is not included in either group
• One of the largest Kuiper objects
The planets
drawn to scale
Figure 22.2
Overview of the solar system
Planets are composed of
• Gases
• Hydrogen
• Helium
• Rocks
• Silicate minerals
• Metallic iron
• Ices
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Ammonia (NH3)
Methane (CH4)
Carbon dioxide (CO2)
Water (H2O)
Evolution of the planets
Nebular hypothesis
• Planets formed about 4.6 billion years ago
• Solar system condensed from a gaseous nebula
• Nebula – a cloud of interstellar gas and dust
As the planets formed, the materials that compose
them separated
• Dense metallic elements (iron and nickel) sank toward
their centers
• Lighter elements (silicate minerals, oxygen, hydrogen)
migrated toward their surfaces
• Processes responsible called chemical differentiation
and mass sorting
Evolution of the planets
Due to their surface gravities, Venus and
Earth retained atmospheric gases
Due to frigid temperatures, the Jovian
planets contain a high percentage of ices,
especially smaller and colder Uranus and
Neptune
Earth's Moon
General characteristics
• Diameter of 3475 kilometers (2150 miles) is
unusually large compared to its parent planet (1/4
the size of the Earth)
• Density
• 3.3 times that of water
• Comparable to Earth's crustal rocks and mantle
• Perhaps the Moon has a small iron core
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Gravitational attraction is one-sixth of Earth's
No atmosphere
Tectonics no longer active
Surface is bombarded by micrometeorites from space
which gradually makes the landscape smooth
Major topographic features
on the lunar surface
Figure 22.6
Earth's Moon
Lunar surface
• Two types of terrain
• Maria (singular, mare), Latin for "sea"
• Dark regions
• Fairly smooth lowlands
• Originated from asteroid impacts and lava flooding the
surface
• Highlands
• Bright, densely cratered regions
• Make up most of the Moon
• Make up all of the "back" side of the Moon
• Older than maria
Earth's Moon
Lunar surface
• Craters
• Most obvious features of the lunar surface
• Most are produced by an impact from a meteoroid
which produces
• Ejecta
• Occasional rays (associated with younger
craters)
A 20-kilometer-wide crater
on the Moon
Figure 22.5
Earth's Moon
Lunar surface
• Lunar regolith
• Covers all lunar terrains
• Gray, unconsolidated debris
• Composed of
• Igneous rocks
• Glass beads
• Fine lunar dust
• "Soil-like" layer produced by meteoric
bombardment
Earth's Moon
Lunar history
• Hypothesis suggests that a Mars-sized object
collided with Earth to produce the Moon
• Older areas have a higher density
• Younger areas are smoother
• Moon evolved in three phases
• I. Original crust (highlands)
• As Moon formed, its outer shell melted, cooled,
solidified, and became the highlands
• About 4.5 billion years ago, just after collision
Earth's Moon
Lunar history
• Moon evolved in three phases
• II. Formation of maria basins
• Younger than highlands
• Between 3.2 and 3.8 billion years old
• III. Formation of rayed craters
• Material ejected from craters is still visible
• e.g., Copernicus (a rayed crater)
Planets: a brief tour
Mercury
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Innermost planet, not too different from the moon
Smallest planet, if one excludes Pluto
No atmosphere (too small and warm)
Cratered highlands
Vast, smooth terrains
Dense (large iron core)
Revolves quickly
Rotates slowly (night side is frigid)
Absorbs most light that hits it, reflects only 6%
Photomosaic
of Mercury
Figure 22.8
Planets: a brief tour
Venus
• Second to the Moon in brilliance
• Similar to Earth in
• Size
• Density
• Location in the solar system
• Shrouded in thick clouds
• Impenetrable by visible light
• Atmosphere is 97% carbon dioxide, 900 deg sfc T
• Surface atmospheric pressure is 90 times that of
Earth's
Planets: a brief tour
Venus
• Surface
• Mapped by radar
• Features
• 80% of surface is subdued plains that are
mantled by volcanic flows
• Low density of impact craters
• Tectonic deformation must have been active
during the recent geologic past
• Thousands of volcanic structures
Computer generated view
of Venus
Figure 22.9
Planets: a brief tour
Mars
• Called the "Red Planet"
• Atmosphere
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1% as dense as Earth's, most lost to space
Primarily carbon dioxide
Cold polar temperatures (-193ºF)
Polar caps of water ice, covered by a thin layer of
frozen carbon dioxide
• Extensive dust storms with winds up to 270
kilometers (170 miles) per hour
Planets: a brief tour
Mars
• Surface
• Numerous large volcanoes – largest is Olympus
Mons
• Northern portion may have been covered by oceans
or seas billions of years ago
• Less-abundant impact craters
• Tectonically dead
• Several canyons
• Valles Marineras – the largest canyon
Olympus Mons, an inactive
shield volcano on Mars
Figure 22.11
The Valles Marineris canyon
system on Mars
Figure 22.12
Planets: a brief tour
Mars
• Surface
• "Stream drainage" patterns
• Found in some valleys
• No bodies of surface water on the planet remain
• Possible origins
• Past rainfall
• Surface material collapses as the subsurface ice melts
• Old ocean that has evaporated away into space
• Moons
• Two moons (both are tiny)
• Phobos
• Deimos
• Captured asteroids
Planets: a brief tour
Jupiter
• Largest planet, usually second brightest
• Very massive
• 2.5 times more massive than combined mass of
the planets, satellites, and asteroids
• If it had been seventy-five times more massive, it
would have been a small star (brown dwarf)
• Rapid rotation
• Slightly less than 10 hours
• Bulges at equator
Comparison
of Earth and
Jupiter
Planets: a brief tour
Jupiter
• Banded appearance
• Multicolored
• Bands are aligned parallel to Jupiter's equator
• Generated by wind systems and rapid rotation of planet
• Great Red Spot
• In planet's southern hemisphere
• Counterclockwise rotating cyclonic storm
• Structure
• Surface thought to be a gigantic ocean of liquid hydrogen
• Halfway into the interior, pressure causes liquid hydrogen to
turn into liquid metallic hydrogen
• Rocky and metallic material probably exists in a central core
Jupiter
Planets: a brief tour
• Moons
• 50 moons + (like Saturn)
• Four largest moons
• Discovered by Galileo, called Galilean satellites
• Callisto - outermost Galilean moon, old surface
• Ganymede - largest moon in solar system,
between Mercury and Mars in size
• Europa - smallest Galilean moon (liquid water
probably underneath thick ice surface)
• Io - innermost Galilean moon and is also
volcanically active
• The interiors of Io and Europa are warmed by
stresses from Jupiter’s gravity (“tidal forces”)
A volcanic
eruption on
Io
Planets: a brief tour
Saturn
• Similar to Jupiter in its
• Atmosphere
• Composition
• Internal structure (less dense and more oblique, though)
• Rings
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Most prominent feature
Discovered by Galileo in 1610
Complex
Composed of small particles (moonlets) that orbit the planet
• Most rings fall into one of two categories based on particle
density
• Thought to be debris ejected from moons or bits of a moon
that was destroyed ~100 million years ago
The ring system of Saturn
Figure 22.18
Planets: a brief tour
Saturn
• Other features
• Dynamic atmosphere, windiest of the planets
• Large cyclonic storms similar to Jupiter's Great Red
Spot
• Titan – the largest Saturnian moon
• Second largest moon (Jupiter's Ganymede is
larger) in the solar system
• Has a substantial atmosphere (80% Nitrogen)
that is thicker than Earth’s
• Liquid hydrocarbon lakes on surface
Planets: a brief tour
Uranus
• Uranus and Neptune are nearly twins, both with
several icy satellites
• Uranus rotates "on its side”
• Atmosphere currently rather bland in terms of
striking cloud features
• Rings second most prominent of the gas giants
• Large moons have varied terrains
Planets: a brief tour
Neptune
• Dynamic atmosphere
• One of the windiest places in the solar system
• Great Dark Spot (like Jupiter’s Red Spot)
• White cirrus-like clouds above the main cloud deck
• Triton – largest Neptune moon
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Orbit is retrograde, captured Kuiper object?
Low surface temperature (-391ºF)
Atmosphere of mostly nitrogen, along with methane
Volcanic-like activity
Composed largely of water ice, covered with layers of solid
nitrogen and methane
• Furthest out of the seven big solar system moons (Earth’s
moon, 4 Galilean satellites, and Saturn’s Titan)
Planets: a brief tour
Pluto (no longer a planet?)
• Not visible with the unaided eye (like Neptune)
• Discovered in 1930
• Highly elongated orbit causes it to occasionally
travel inside the orbit of Neptune, where it
resided from 1979 thru 1999
• Moon (Charon) discovered in 1978, but now it
is considered a dwarf planet like Pluto.
• Average temperature is -210ºC
Pluto and its moon Charon as
compared to the size of Earth
Figure 22.18
Minor members of the solar system
Asteroids
• Most lie between Mars and Jupiter
• Small bodies – largest (Ceres) is about 620 miles
in diameter
• Some have very eccentric orbits
• Many of the recent impacts on the Moon and
Earth were collisions with asteroids
• Irregular shapes except largest half dozen or
so, which are spherical
• A few visible to naked eye when brightest
The orbits of most asteroids
lie between Mars and Jupiter
Image of asteroid 951 (Gaspra)
What determines a planet?
New criteria adopted for describing a planet:
• Must be massive enough to pull themselves into a
sphere due to their own gravity (good criterion)
• Must have enough mass to “clear their orbit”
-- This is a more questionable assertion
-- Neptune, while much more massive than inner
planets, has a huge orbit that it cannot clear
-- This is why Pluto was not called an official
planet. Neptune has problems with this point, too,
but it seems to be ignored.
-- This is a bad criterion and may be fixed later.
Minor members of the solar system
Comets
• Often compared to large, "dirty snowballs”
• Now found to be more rock, with some ice
• Composition
• Rocky and metallic materials
• Frozen gases
• Frozen gases vaporize when near the Sun
• Produces a glowing head called the coma
• Some may develop a tail that points away from Sun due
to
• Radiation pressure
• Solar wind
Orientation of a comet’s tail
as it orbits the Sun
Gas (ion) tail always points
directly away from sun due
to solar wind. Dust tail is
often broader and is affected
by orbital motion as well as
the solar wind.
Figure 22.25
Minor members of the
solar system
Comets
• Origin
• Many form at great distance from the Sun
• Bright comets are usually long period
• Most famous short-period (< 200 years) comet
is Halley's comet
• 76 year orbital period
• Potato-shaped nucleus (16 km by 8 km)
• Responsible for two meteor showers (Eta Aquarids
in May and Orionids in October)
Comet Hale-Bopp
Figure 22.26
Minor members of the
solar system
Meteoroids
• Called meteors when they enter Earth's
atmosphere
• A meteor shower occurs when Earth encounters
a swarm of meteoroids associated with a
comet's or asteroid’s path
• Meteoroids are referred to as meteorites when
they are found on Earth, must be large enough
to not completely burn up, as vast majority do
Minor members of the solar system
Types of meteorites classified by their composition
--Give an idea as to the composition of Earth’s core
--Help provide an age of the solar system, little changed
• Irons
• Mostly iron, dense
• 5-20% nickel
• Stony
• Silicate minerals with
• Inclusions of other minerals
• Stony-irons – mixtures
• Carbonaceous chondrites
• Rare
• Composition – organic material, simple amino acids?
Minor members of the solar
system
Meteorites
• Good percentage of meteorites large enough to
make it through the Earth’s atmosphere originated
in the asteroid belt
• Collide with other asteroids and deflected toward the
Earth
• As meteors enter the atmosphere friction caused by the
air produces large amounts of heat that produce light
• Meteor Crater Arizona – believed to occur in the last
20,000 years
• The cavity is ¾ mile wide and 560 ft deep
Earth’s tectonic activity erases most craters
A Taurid fireball
(very bright
meteor)
The Taurids are
one of many
meteor showers.
This particular
shower is
characterized by
slow and, in
some years, very
bright meteors.
End of Chapter 23