Review Worksheet
Solutions
1. Describe the focus of comparative
planetology and discuss its importance to solar
system studies.
Comparative planetology is the approach we
use to study and understand our solar
system. It involves comparing the worlds of
our system, including planets, moons,
asteroids, and comets, to one another. Its
basic premise is that the similarities and
differences among the worlds can be traced
to common physical processes.
2. Briefly outline the theory or hypothesis which best
explains the origin of the solar system and explain how
the observable properties of the solar system are
related to its process of formation.
• A large nebula began to
collapse gravitationally. As it
did so, it began to spin faster,
and flattened into a disk and
heated up.
• Planetisimals were formed by
accretion of small particles
that collided & stuck together
growing larger.
• The greater gravity of
planetisimals attracted
more materials and
they grew larger,
forming planets.
Leftover debris became
asteroids and comets.
• All the orbital and rotational motions can be
explained as preserving the original rotation of
the nebula from which the solar system formed.
• Accretion explains planetary isolation.
• Temperature differences explain differentiation.
• Irregularities can be explained by collisions during
the planetisimal era
3. Compare and contrast the formation of Jovian
planets to that of terrestrial planets.
• The terrestrial planets are composed primarily of denser materials
that condensed in the hotter part of the solar nebula.
• The Jovian planets contain not only the metallic and rocky
compounds but also the hydrogen compounds which condensed in
the colder part of the nebula, outside the frost line.
• Since these materials made up a larger percentage of the nebula,
these planetisimals were able to accrete more material.
• This allowed their greater gravity to attract the lighter hydrogen and
helium gas. As a result, the Jovian planets have thick atmospheres.
4. In the context of planet formation, what are asteroids and
comets? Briefly explain why we find asteroids in the asteroid belt
and comets in the Kuiper belt and Oort cloud.
• Asteroids and comets are
the leftover planetisimals
that never accreted enough
material to form planets.
• Asteroids formed inside the
frostline, comets formed
outside the frost line. The
asteroids are kept in the
asteroid belt by the
gravitational influence of
Jupiter.
•
• Comets that formed
beyond the orbit of
Neptune orbit in the
Kuiper belt.
• Comets that formed
where the Jovian
planets are were flung
into extreme orbits by
Jupiter and the other
large Jovian planets.
5. Summarize the basic differences between the
terrestrial and the Jovian planets.
• Terrestrial planets are metallic or rocky in
composition, close to the Sun, are warmer at
the surface, have higher average density, have
a solid surface, and have few if any moons.
• Jovian planets are gaseous in composition,
lower in density, have no solid surface, are
farther from the Sun, and have rings and
moons
6. Describe and distinguish between space missions
and discuss the advantages and disadvantages of each.
• flyby- lowest cost, easiest type of mission
however, can’t do sustained studies, try to
capture images/data on the fly
• Orbiter- costs more & takes more planning but
allows for long term studies
• Lander – more costly & more planning, also
requires extra fuel for descent to surface, more
danger of damage but gives high res images of
surface and can study samples. Can collect info
on surface comp, temp, pressure, etc.
• Sample return- most expensive, heaviest load.
7. Describe how the moon formed and the evidence to
support this hypothesis.
• The Moon formed from a giant impact of a Mars-size
object with the earth. This impact destroyed the
body and blasted material from the Earth’s mantle
into orbit. This material eventually coalesced to form
the Moon.
• Three pieces of evidence are:
• the composition of the Moon is similar to that
of the earth’s outer layers,
• the Moon is depleted of easily vaporized
materials, as we would expect from the heat
of an impact
• computer simulations show that the Moon
could really have formed this way
8. Explain why the early Earth did not form with water,
and how it gained it later in its formation.
• Earth, and all terrestrial planets, formed inside the
frost line from rocky and metallic planetisimals.
• The temperature of the solar nebula was too hot for
water ice to exist and the earth was too small to hold
onto a substantial atmosphere of hot gases.
• Earth gained its water later during the heavy
bombardment phase.
• Water-rich planetisimals (or comets) that formed
beyond the frost line were scattered into the inner
solar system, predominantly through gravitational
encounters with Jupiter, and impacted the earth.
9. If a fossil is found to contain a sixteenth as much
Carbon-14 as a living organism, what is the percent of
Carbon-14 remaining? If the half life of Carbon-14 is
5, 715 years, how old is the fossil?
1/16 = (½ )4 so four half lives have gone by
this means the fossil is about
5715 x 4 = 22,860 years old
the percent remaining is (1/16) x 100 = 6.25 %