Physical Geology 101
37. Planetary Geology
p. 656-679
The Solar System Revisited
We will now apply all the information we have learned about the geology of the earth to other planetary bodies
to see how similar, or different, they are to our planet.
There are a total of _____ planets that comprise our solar system. Once the most distant planet from the Sun,
Pluto is now relegated to the status _________________, and is 40 times further from the Sun than Earth,
which we represent by the abbreviation 40 AU.
An AU is an __________________________________(1 AU is the distance from the Earth to the Sun).
At a distance of 30-50 AU is a wide ring of small icy bodies outside of the region of named planets. This part of
the solar system is called the _____________________________.
Even further out from here is the _________________________: an enormous collection of icy bodies that is
the source of many comets. Other comets come from the Kuiper Belt.
What Kuiper Belt object discovered in 2002 is over 1000 km in diameter? ____________________
Since then, several other distant solar system bodies have been discovered inside the Kuiper Belt, including
one object discovered in 2005 and determined in April 2006 to be larger than Pluto. This object is now officially
a dwarf planet named __________________.
In 2004, a body was discovered orbiting the Sun outside the Kuiper Belt but inside the Oort Cloud, at about 90
AU. This body is slightly smaller than Pluto and is the most distant known body that orbits the Sun (once every
10,500 years). Its name is ____________________.
More Kuiper Belt objects may be discovered in future that rival Pluto in size and may even be considered for
designation as dwarf planets.
All of the planets revolve around the Sun in the same direction. If we were to look down on the solar system
from above its north pole, all the planets would be moving in a ___________________________ direction in
approximately circular orbits around the Sun.
The planets are all aligned within a flat imaginary plane, called the ________________________________.
In contrast, _____________ has a highly elliptical orbit inclined at 17° to this plane, causing it to sometimes
pass inside Neptune's orbit.
When viewed from above, six of the planets rotate in a ____________________________ manner around
their rotational axes. So, like Earth, on most planets, the Sun rises in the east and sets in the west.
What two planets rotate in a clockwise manner? ___________________ and ____________________
One of the planets has somehow managed to roll over on its side with respect to the plane of the ecliptic. The
northern hemisphere always faces the Sun and the southern hemisphere always faces away from it. What
planet is this? _____________________
Between the orbits of Mars and Jupiter is a huge belt of rocks and debris called the ____________________.
They owe their existence to Jupiter's large size and strong gravitational field which prevented early solar
system planetesimals in this region from ever coalescing into a planet.
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Physical Geology 101
The composition and evolutionary history of the planets are a consequence of their distance from the Sun.
The innermost planets are called the ____________________________.
List the terrestrial planets (in order from the Sun):
_______________
________________
________________
________________
The terrestrial planets are all composed of rocks with metallic and nonmetallic elements. So they also have
high densities. The rocks and metallic elements that constitute the terrestrial planets must have condensed at
high temperatures, which would be expected closer to the center of the collapsing disk during the formation of
the solar system. That's why the terrestrial planets are closest to the Sun.
The planets further away from the Sun are called the _________________________.
List the Jovian planets (in order away from the Sun):
_______________
________________
________________
________________
The Jovian planets all have low densities because they are mostly made of the gases _________________
and __________________, with frozen compounds like ammonia and methane, surrounding small rocky
cores. These predominantly gaseous bodies must have condensed at much lower temperatures, which would
be expected around the outer portions of the collapsing disk of the primordial solar system. Because they are
so large and gaseous, the Jovian planets are also referred to as the _______________________.
During the early development of the solar system, collisions between planetesimals were common. That's
why we see so many ________________ on the surfaces of the planets and moons. A large collision
between a planetesimal and Venus may be the reason for its clockwise rotation. Similar collisions may be
responsible for Uranus lying on its side and for Pluto revolving so far off the plane of the ecliptic and making
fun of the rest of the solar system.
Meteorites
Space debris that enters the Earth's atmosphere are called _______________. They usually vaporize in the
upper atmosphere due to frictional heating, producing so-called shooting stars. If they collide with the Earth’s
surface they are called __________________.
Meteorites don't have to be very big to cause a lot of damage. Small meteorites hit Earth every day (10-50 of
them), and have the potential to cause damage, injuries, or death.
Larger meteorites, perhaps a few 100s of meters across, can create enormous craters, like Barringer Meteor
Crater in Arizona, which resulted from an asteroid hitting the Earth _________________ years ago.
Even larger meteorites can irrevocably alter the evolution of the planet, such as the 10 km big
______________________ meteorite impact that ultimately caused the extinction of the dinosaurs.
Where did this impact occur? ______________________________.
When did it occur? _____________________ years ago.
What two geologic time periods have their boundary at this point in geologic time?
____________________ and ____________________ (the “K-T” Boundary)
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Physical Geology 101
What element, known to be common in meteorites, is enriched in clay layers that formed at the K-T boundary?
___________________
Despite being a potential threat, meteorites have helped us learn a lot about the earliest times of the solar
system because many of these meteorites are actually bits of debris that formed when the solar system first
began to form.
The solar system cleared out most of this debris through collisions early in its history, so there is less meteorite
activity today than there would have been early in Earth's history.
Meteorites are classified into 3 categories based on their compositions:
TYPE
ABUNDANCE

_________________ meteorites
93%

_________________ meteorites
6%

_________________ meteorites
1%
Most meteorites are stony meteorites, which are composed of iron and magnesium silicate minerals that
formed during the very beginning of the solar system's history.
What are the three types of stony meteorites?
1. ________________________________ (like mantle or crustal material)
2. ________________________________ (rare primordial solar nebula material)
3. ________________________________(like Earth basalts- but come from the Moon or Mars)
Iron meteorites are composed of iron and nickel alloys so they are often considered to be an analog for the
Earth’s core. They likely represent the cores of asteroids that were broken apart by collisions with other
asteroids. Stony-iron meteorites are composed of almost an equal ratio of Fe/Ni alloys and silicate minerals.
Planets and Moons
Terrestrial Planets
The terrestrial planets had similar beginnings to Earth. The mass, density, and composition of each planet
suggests that each developed an ___________________ surrounded by a _______________________ and
______________. Atmospheres developed through the outgassing of light gases from the planetary interiors
during periods of volcanism.

Mercury: is about 40% the size of Earth and has changed little since it first formed. About 80% of its mass
is due to a large metallic core. A slight magnetic field indicates that the core must be ________________
_______________. The surface is heavily cratered and many craters appear to be filled with undisturbed
lava flows. Because of its small gravity, all the gases escaped into space so Mercury has no atmosphere.
Does Mercury have any current tectonic activity?
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YES or NO
Physical Geology 101


Venus: is about _______% the size of Earth but otherwise is very different. Its surface temperature is
________°C (Earth is about 25°C!). The atmosphere contains 96% CO 2. Venus has a core, mantle, and
crust. There is no evidence of active volcanism, although volcanic lava domes and old lava flows are
visible.
Does Venus have any current tectonic activity?
YES or NO
Has Venus been tectonically active in the past?
YES or NO
Mars: about ______% the size of Earth; has a core, mantle and crust. The atmosphere is thin, with
95% CO2.
The southern hemisphere is heavily cratered, including the largest impact crater in the solar system, called
_________________________, which has a crater 2,000 km wide.
The northern hemisphere is a flat, smooth plain, and is believed to represent an ____________________
_____________________, with evidence of ancient erosional shorelines.
The largest volcano in the solar system is on Mars: __________________________________
It is 27 km high, 3 times higher than Mt. Everest. It is so large because Mars has no plate tectonics, so the
hotspot that formed it stayed in the same place below the Martian crust.
Does Mars show evidence of tectonic activity?
YES or NO
Evidence: Mars has numerous faults, as well as the largest rift valley in the solar system, called
______________________. It is 250 km wide, 7 km deep, and 4,000 km long. It would stretch from San
Francisco to New York.
Recent images have provided strong evidence that ______________ has flowed across the Martian
surface in the past as giant rivers.
Could liquid water exist on the surface of Mars today? YES or NO
Despite the extreme cold, there is evidence of recent water or ice flows out of rock faces- perhaps surface
seeps that come from vast groundwater aquifers.
Jovian Planets
The Jovian planets were imaged by the Voyager spacecraft missions. Jupiter is 11 times bigger than Earth,
Saturn is 9.5 times bigger, and Uranus and Neptune are both about 4 times bigger. All are predominantly
gaseous, with rocky cores, and all have ring systems around them.
Jupiter has at least 28 moons, including the most volcanically active body in the solar system, called
________. There are only 3 other volcanically active bodies: Earth, Neptune’s moon _______________, and
Saturn’s moon _________________ (which erupts water ice).
Another of Saturn’s moons, ___________________ is larger than planet Mercury and is the only moon in the
solar system with an atmosphere (mostly nitrogen, like Earth). It is also the only moon (other than our own) on
which we have landed a human-made spacecraft (the Huygens probe, during the Cassini mission). Titan has a
surface covered in pools of liquid hydrocarbons and shows evidence of frozen methane sand dunes.
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Physical Geology 101
Jupiter also has a moon which has the greatest potential of all the other bodies in the solar system of harboring
life due to a vast water ocean below an ice crust. Its name is ___________________.
The Earth-Moon System
The Moon is about ______% the size of Earth, and, like Earth, has a metallic core, and a silicate mantle and
crust. We know the innermost part of the mantle is partially molten because it doesn't transmit S-waves
generated by small moonquakes deep in the mantle.
The surface is mostly composed of the igneous rock ________________, which is mostly feldspar. The other
rock type present is ________________ which forms the low-lying dark plains, called ______________
(singular: mare) which cover about 17% of the surface. They probably formed from partial melting of a silicate
mantle, possibly during meteorite impacts.
How did Earth’s moon form? _____________________________________________________________
This happened about 4.6 to 4.4 billion years ago. A large portion of Earth's hot early mantle material was
ripped away and coalesced and differentiated to form the Moon, which remained in orbit around the Earth.
FINAL QUESTIONS:
What’s your favorite celestial body?!
_________________________
Your favorite class this semester was (pick from the following list):
(a) Geol 101
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