Download Chapter 16: The Origin of the Solar System RQ 16

Chapter 16: The Origin of the Solar System
RQ 16-2
Q: What produced the iron in Earth’s core and the heavier elements like gold and silver in
Earth’s crust?
A: The heavier elements in the Earth’s crust and core were produced during generations
of stars before the solar system was born. The elements up to iron were built by nuclear
fusion during the lifetimes of previous stars. Elements heavier than iron were built during
super nova explosions. These explosions also helped to spread the newly produced
elements into space. The nebula, which became then our solar system consisted of this
kind of ejected material. Every gram of our body or of the Earth’s soil was once a part of
the interior of a star.
RQ 16-4
Q: According to the solar nebula theory, why is the sun’s equator nearly in the plane of
Earth’s orbit?
A: According to the solar nebula theory, the sun and the planets originate all from the
same spinning cloud of matter. This cloud collapsed into a disk perpendicular to the axis
of rotation. Since the sun was part of this disk, its axis of rotation is about the same as the
axis of rotation of the original disk. The Earth consists of material originating from a part
of the dust and gas disk. Therefore, in order to conserve angular momentum, the Earth’s
orbit has an axis nearly parallel to the original disk’s axis of rotation and this is also the
reason, why the sun’s equator is nearly in the Earth’s orbit.
RQ 16-9
Q: What is the difference between condensation and accretion?
A: Condensation means that larger particles are built by adding molecules or atoms to
them. This is a process in which gaseous matter is transformed to solid matter. It takes
place on the microscopic scale and depends very much on the surface of the involved
particles (chemical properties).
Accretion, on the other hand, is the adding of larger particles. As the involved system of
particles is still small, the surface is still a factor in terms of how well these particles stick
together (e.g. ice pieces stick better together than pieces of rock). However, when the
system has accumulated enough mass, gravity takes on an important role in holding the
conglomerate together.
RQ 16-12
Q: How does the solar nebula theory explain the dramatic density difference between the
terrestrial and Jovian planets?
A: The difference in the density of terrestrial and Jovian planets can be explained by the
different ability of materials (elements, molecules) to condense at a certain temperature
(condensation sequence). In the case of the terrestrial planets, the gas was so hot (since it
was near to the center of the system), that only matters with high “boiling points” were
able to condense. Therefore, only metals and then also silicates could condense to form
solids. At these inner orbits, material with lower boiling points (lighter elements) could
not be collected, since it still was in its gaseous state. This way the inner planets
selectively were made out of heavy elements and thus have now high densities.
At greater distance from the center, matter like water ice and methane ice could condense
and more and more pieces could stick together. Therefore, the Jovian planets started to
form from these icy grains consisting mostly of light elements. The Jovians contain both
heavy and light elements due to cooler temperatures of the outer solar system during its
formation but a much higher fraction of light elements since they were more abundant in
the primeval solar nebula. This is the reason why these planets have lower densities than
the terrestrial planets.
Problem 16-1
The nearest star is about 4.2 ly away. If you looked back at the solar system from that
distance, what would the maximum angular separation be between Jupiter and the sun?
(Hint: 1 ly equals 63,000 AU.)
Solution:
The distance to our solar system is D=4.2 ly = 264600 AU. The radius of the jovian orbit
is d=5.2 AU.
Using the small -angle formula,
Θ
d
= ,
206,265 D
the maximum angular separation between Jupiter and the sun is:
d × 206,265 5.2 × 206,265
Θ=
=
= 4.00′′
D
4.2
Jupiter and the sun would be separated by 4 seconds of arc.
Problem 16-5
In Table 16-2, which object’s density differs least from its uncompressed density? Why?
Solution:
The Moon’s density (3.36 g/cm3) differs least from its uncompressed density
(3.40g/cm3):
3.36 − 3.40
Δ=
× 100 % = -1.2%
3.40
The Moon’s observed density is 1.2% smaller than its uncompressed density. The reason
why the Moon’s density is so close to its uncompressed density is that it is, compared to
Mars, Earth or Venus, such a small body that its gravity did not compress the Moon’s
interior as much as in the other planets.
Problem 16-7
Suppose that Earth grew to its present size in 10 million years through the accretion of
particles averaging 100g each. On the average, how many particles did Earth capture per
second? (Hint: See Appendix A to find Earth’s mass.)
Solution:
The total mass of the Earth is M=5.976x1024kg. If the average particle size had a mass of
M
= 5.976 × 10 25 of these
m=100g=0.1kg, this means the Earth had to collect n =
m
particles in 1x107years. Which is,
365d 24h 60m 60 s
1 × 10 7 years ×
×
×
×
= 3.156 × 1014 sec
yr
d
h
m
This means the Earth collected
5.976 × 10 25 particles
particles
~
n=
= 1.9 × 1011
14
sec ond
3.156 × 10 sec onds