1)Describe the overall layout of the solar system. What are the 3 major features of our solar system that provide
clues to how it formed?
(1) planetary motions are mostly orderly: orbits and rotations are in the same direction and with generally
small tilts;
(2) there are two types of planets, jovian and terrestrial, with very different properties and locations;
(3) there are also two classes of “small bodies,” comets and asteroids, also with distinct properties and
locations;
2) Describe the patterns of motion that we observe among the planets and their orderly motion in our solar system:
- Planets all orbit in nearly the same plane and have nearly circular orbits.
- Planets orbit the Sun in the same direction.
- Most planets spin in the same direction as they orbit
3) what are the basic differences between the Terrestrial and Jovian planets? Which planets fall in each group?
Terrestrial planets orbit close to the Sun and are tightly spaced together. They are made mostly of rock and
metal and are smaller and denser than Jovian planets. Terrestrial planets tend to have few, if any, moons
and none have rings.
In contrast, Jovian planets are more distant from the Sun and are separated by much larger distances. They
are made mostly of hydrogen, helium, and hydrogen compounds. They are much less dense than terrestrial
planets. They are also larger than terrestrial planets. Jovian planets have many moons and have ring
systems.
The terrestrial planets are Mercury, Venus, Earth, and Mars. The Jovian planets are Jupiter, Saturn,
Uranus, and Neptune. Pluto does not fit into either class.
what is the Kuiper Belt? What is the Oort Cloud? How do the orbits of comets differ in the two regions?
The Kuiper belt is a disk of comets just past the orbit of Neptune. The Oort cloud is a spherical cloud of
comets that surrounds
our solar system much
farther from the Sun.
Comets in the Kuiper
belt orbit the Sun more
or less in the same
plane as the planets
and travel around the
Sun in the same sense
as the planets do. Oort
cloud comets orbit the
Sun randomly in all
direction and
surrounding the Sun
like a cloud.
5) Describe the four major features of our solar system that formation theory must explain:
The first property is the fact that the motions in our solar system are orderly. The planets orbit in the same
plane, on nearly circular orbits, and in the same direction around the Sun, and most of them spin in that
same sense. Most of the major moons of our solar system also follow these rules when orbiting around their
planets.
The second property of the solar system that provides clues about the formation is the existence of two
kinds of planets, Jovian and terrestrial. The two types of planets are found in different parts of the solar
system (outer and inner, respectively) and are generally very different in nature. (Masses, densities, and
compositions are especially significant differences.)
The third property we use to understand the formation of our solar system is the existence of smaller bodies
such as comets and asteroids. Asteroids are rocky or metallic bodies that are usually found between the
orbits of Jupiter and Mars. Comets are icy bodies found farther out in the solar system. Comets are found
in two regions, the Oort cloud and the Kuiper belt.
Finally, the fourth property, there are exceptions to the rules. Venus spins backward, Uranus and Pluto spin
on their sides, Earth has an incredibly large moon for a terrestrial planet, and a number of smaller moons
(plus the large moon Triton) orbit their planets backward.
6) what is the nebular theory and the formation of the solar system?
The nebular theory states that the solar system formed from a collapsing cloud of gas and dust billions of
years ago. The nebula itself came from dying stars which enriched the nebula with heavy elements like
Carbon, Oxygen, Nitrogen, metals….etc
7) Describe key processes that let the solar nebula to take the form of a spinning disk. What observational evidence
supports this scenario?
The cloud that formed the solar system began by collapsing under its own gravity. As it did so, it spun faster
to conserve angular momentum. Most of the gas collapsed at the center to make the ‘baby star’ while the
left over material gas and dust flattened into a disk called accretion disk. The solar nebula eventually took
on a disk shape spinning around newly born star. Evidence for these processes can be found in the fact
that the planets orbit the Sun in nearly the same plane and in the same direction and that they spin in this
same direction.
8) How planetesimal forms?
When clumps of gas and dust collided in the accretion disk, they stuck together to form bigger object of
rocks. Those rocks started to sweep all the material available on their path and grew bigger into
planetesimals. Those planetesimals are baby planets.
9) What is angular momentum? How angular momentum affect the formation of planets?
Gravity cause the nebular to collapse into itself. However, Angular momentum causes the nebula to spin
faster and faster as it shrinks in size. Most of the nebula collapse as a to form a star at the center (the Sun)
the remaining material, as it spins faster, the gets flattened into a disk, the accretion disk, where planets
are formed. With no angular momentum, the entire nebula would collapse into a star, with no disk from
which to make planets.
10) Describe the composition of solar nebula. Which ingredients are present in planets? In Jovian planets? In
comets & asteroids?
Gases = hydrogen and helium — They are the most abundant ingredient: ~98% and came directly from
the Big Bang.
* the remaining 2% is basically the heavier elements or “metals” what came from dying stars: like Oxygen,
Carbon, Nitrogen, Ca, Fe,…..…and all other elements from the period table.
The terrestrial planets are mainly made up of rocks (silicates) and metals, which explains their high
densities. The Jovian planets are mainly made up of the gases and the hydrogen compounds, which explains
both their lower densities and why they are so large: There was so much more material for them to be built
from. Asteroids are mostly rock and metal, while comets are icy objects mostly hydrogen compounds with
some rock and metal
11) What is the frostline and its role of the formation of planets?
The frost line is the point moving away from the Sun where it is cool enough for water and hydrogen
compounds to freeze. The frost line is located between Mars & Jupiter. Since the solar nebula was hotter near
the center of the disk, hydrogen compounds
such as water stayed gaseous in the inner
solar system. Outside of the frost line, they
froze. As solids, these compounds were able
to participate in building planets. Since
there was so much more water (and, farther
out, solid ammonia and methane) in the
outer portion of the nebula, the “seeds” of
the planets that formed beyond the frost line
were much larger than the ones inside that
limit. The large size of these Jovian planet
“seeds” allowed them to gather
hydrogen/helium gas and make gaseous
planets.
12) describe the process of formation of Terrestrial planets:
The terrestrial planets are thought to have been formed by solid bits of silicates and metals colliding and
sticking together in the flattened accretion disk. The silicates and metals were able to condense in the hotter
inner part of the disk where the temperature was too high for hydrogen compounds to become solids. As
the silicates formed larger clumps, their gravity began to allow them to gather up mass more efficiently.
The biggest bodies, now called planetesimals, were able to collect mass the fastest. Eventually, the biggest
planetesimals gathered up the others and became planets.
13) describe the process of formation of Jovian planets? How is it different than Terrestrial planets?
The formation of the Jovian planets was similar to that of the terrestrial planets in the early stages, with the
major exception that the Jovian planets were able to use solid hydrogen compounds (ices) to build up their
masses. Since these ices were far more abundant than the silicates and metals, the Jovian planets were able
to grow faster and become larger than the terrestrial planets. Eventually, they became large enough to hold
on to nebular gases (hydrogen and helium). In this respect their formation was quite different from that of
the terrestrial worlds. Once the Jovian planets could collect gas, it was easy for them to grow very large.
(Jupiter and Saturn in particular were able to grow extremely massive relative to the terrestrial planets.)
14) how did planet formation lead to the existence of asteroids and comets?
Asteroids and comets are essentially leftovers from planet formation. They are bits of material that were
never swept up into planets.
We find rocky asteroids in the inner solar system (in the asteroid belt between Mars and Jupiter, mainly).
Farther out, where hydrogen compounds were able to condense into ices, the small leftover bodies were
icy—and so we have comets.
15) what is the heavy bombardment, and when did it occur?
The heavy bombardment was a period when many comets or asteroids were striking the planets. This
bombardment occurred near the end of planet formation or early in the solar system’s life, within the first
few hundred million years.
16) Formation of the Moon was due to a large impact? Describe this process? Did other planets on the solar
system suffered from large impacts or collisions as well?.
We think that the Moon formed when a large impactor struck Earth with a glancing blow. Such a collision
would have blown a lot of material into orbit around Earth, temporarily forming a disk around our planet.
From this disk, the Moon formed. Evidence in favor of this theory includes the chemical composition of the
Moon: It is similar to Earth’s mantle (which is where the material probably came from) and it is deficient
in easily vaporized compounds like water.
It is not really surprising that such an event could have affected Earth. There are other objects in the solar
system that seem to show the effects of similar collisions. Uranus is tipped over. Pluto is both tipped over
and has a large moon like Earth does. Mercury lacks most of the outer layers we would expect it to have,
which might have been blasted off in a collision.
