Chapter 8
15. Describe the technique of radiometric dating. What is a half-life?
Radiometric dating is the process of determining the age of the rock by comparing the present amount of radioactive substance to the amount of its decay product. This method relies on careful measurement of the proportions of various atoms and isotopes in the rock. A half-life is the time it takes for half of the nuclei in a given quality of a radioactive substance to decay.
14. How do we think the Moon formed, and what evidence supports this hypothesis?
A large Mars sized object hit the young Earth. This was the cause for Earth's tilted axis & change in rotation rate. Using computer simulations, if we consider an impact at the speed and angle that would have blasted rock from Earth's outer layers in space, we can see that this material could have collected into orbit around our planet and accretion within this ring of debris could have formed the Moon. 1) the Moon's overall composition is quite similar to that of Earth's outer layers. 2) the Moon has a much smaller proportion of easily vaporized ingredients than Earth. This supports the hypothesis because the heat of the impact would have vaporized the ingredients.
12. 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: rocky leftover planetesimals of inner solar system between Mars and Jupiter known as the asteroid belt Comets = icy leftover planetesimals of outer solar system past Neptune. They remained in the original orbit which means they now occupy the region of the Kuiper Belt. In contrast, comets between the jovian planets dealt with a lot of gravitational encounters, thus throwing them off their original orbits. They no longer display the original orderly motion of the disk in which the planets are formed and thus now populate the Oort cloud.
8. How was the formation of jovian planets similar to that of the terrestrial planets? How was it different?
Condensation of ices farther out in the solar nebula meant there were more solid materials in addition to the metal and rock. Jovian planets formed as gravity drew gas around ice-rich planetesimals much larger than Earth; (when it gets about 10 Earth masses) therefore they had a strong enough gravity that it could capture and hold hydrogen and helium that made up a vast majority of the material in the solar nebula. After collecting and collecting, they hardly resembled the icy seeds from which they grew.
19. A solar system has five terrestrial planets in its inner solar system and three jovian planets in its outer solar system.
False. A majority of the material in a solar nebula is hydrogen and helium and this material can condense only belong in the frost line. Because there's more material beyond the frost line, it would make more sense that there'd be more jovian planets than terrestrial planets.
20. A solar system has four large jovian planets in its inner solar system and seven small terrestrial planets in its outer solar system.
False. The inner solar system is closer to the sun, therefore containing higher temperatures. Only rock and metal condense at higher temperatures, so the planets formed in the inner solar system must be terrestrial. The outer solar system contains colder temperatures. Only helium and hydrogen compounds can condense at such low temps, so the outer solar system must contain jovian planets.
13. What was the heavy bombardment, and when did it occur?
Heavy bombardment = period of first few 100's of millions of years after the solar system formed during which the tail end of the planetary accretion created most of the craters found on ancient planetary surfaces.
5. List the four categories of materials in the solar nebula by their condensation properties and abundance. Which ingredients are present in terrestrial planets? In jovian planets? In comets and asteroids? Explain why.
Hydrogen and helium: 98% of solar nebula. NEVER CONDENSE Hydrogen compounds (1.4% of solar nebula. Condense into ices below 150K .these include water, methane, and ammonia Rock: 0.4% of solar nebula, Condenses into solid bits of mineral b/t 500-1300K Metal: 0.2% of solar nebula. Condense into solid form at temps b/t 1000-1600K ---The ingredients present in terrestrial planets include rocks and metals because it is hotter closer to the sun where the rocks and metals could condense to form a planet. Farther away from the sun where it requires less temperature to condense hydrogen and helium and hydrogen compounds are where the jovian planets formed. In comets and asteroids, it is carbon-rich minerals that condensed because of the low enough temperature.
17. Suppose the solar wind had cleared away the solar nebula before the seeds of the jovian planets could gravitationally draw in hydrogen and helium gas. How would the planets of the outer solar system be different? Would they still have many moons? Explain your answer in a few sentences.
If the gas giants lacked their massive gaseous atmospheres, they wouldn't have nearly as many moons as they do now due to the huge mass loss that would result. The less mass they have means the less gravitational pull they have which means they have less ability to hold moons in orbit.
22. A solar system has 12 planets that all orbit the star in the same direction and in nearly the same plane. The largest moons in this solar system orbit their planets in nearly the same direction and plane as well. However, several smaller moons have highly inclined orbits around their planets.
No, the smaller moons would be bound to their planets on approximately the same plane due to their masses.
21. A solar system has ten planets that all orbit the star in approximately the same plane. However, five planets orbit in one direction (e.g., counterclockwise), while the other five orbit in the opposite direction (e.g., clockwise).
Not possible. If the planets are orbiting a star in approximately the same plane, they will all orbit in the same direction. Apparent retrogration may occur though.
26. A solar system has several planets similar in composition to the jovian planets of our solar system but similar in mass to the terrestrial planets of our solar system.
Not possible. The jovian planets have their composition because of how large they are. If they were smaller, their densities and compositions would be different.
10. After the protoplanets formed did they change their orbits?
Planets migrate inward then back out due to sun's pull and other planet's gravity [See planetary migration]
27. A solar system has several terrestrial planets and several larger planets made mostly of ice.
Possible. It is more likely that planets that are made of ice would be larger.
16. How old is the solar system, and how do we know?
Radiometric dating shows oldest rocks to be 4.5 billion years old. Observations of the stars show that stars slowly expand and brighten as they age also support it.
11. What is the solar wind, and what roles did it play in the early solar system?
Solar wind-stream of charged particles (protons and electrons) that contrually blows outward in all directions from sun. Although the solar wind is fairly weak today, observations of winds from the other stars show that such winds tend to be much stronger in young stars. The young Sun therefore also should have had a strong solar wind. This swept the hydrogen and helium that made up the solar nebula into interstellar space by some combination of radiation from the young Sun.
25. A solar system has many rocky asteroids and many icy comets. However, most of the comets orbit in the inner solar system, while the asteroids orbit in far-flung regions much like the Kuiper belt and Oort cloud of our solar system.
Surprising. the fact that the farther into the solar system you go, the colder it is. Comets are largely made up of ice because they are formed in the cold regions of the solar systems. Asteroids are made of metal and rock because they are formed much closer to the star.
6. What was the frost line in the solar nebula? Explain how temperature differences led to the formation of two distinct types of planets.
The frost line in the solar nebula lies between Mars and Jupiter. It is the distance where it was cold enough for hydrogen compounds to condense into ices. Temperature differences led to the formation of two distinct types of planets (terrestrial and jovian) b/c of the temperature at which the materials that make up each type of planet could condense. (Ex. Takes a higher temp to condense rock and metal [terrestrial] and a lower temp to condense hydrogen, helium, and hydrogen compounds [jovian]). This also tells us why the jovian planets are so much larger than the terrestrials (b/c hydrogen is most abundant and could only condense farther out from the Sun).
2. What is the nebular theory, and why is it widely accepted by scientists today?
The nebular theory is a modification of the nebular hypothesis which said that the solar system formed from the gravitational collapse of an interstellar cloud of gas. It was formed when scientists used more sophisticated models of the processes that occur in a collapsing cloud of gas. It became a theory because it offered natural explanations for all four of the general features of the solar system (listed in question 1). It is so widely accepted because it successfully predicted the existence of other planetary systems (that we are found recently).
7. Briefly describe the process by which terrestrial planets are thought to have formed.
The process by which terrestrial planets formed is called accretion. It begins with the microscopic solid particles that condensed from the solar nebula's gas. Because the particles orbited the Sun just like the gas that orbited, the particles "collisions" were really just gentle touches- sticking together through electrostatic forces (static electricity). Small particles became larger ones; then, gravity began helping the process of sticking together, which made the growth much faster. These particles became planetesimals ("pieces of planets"). Only the largest planetesimals avoided being shattered and could grow into terrestrial planets.
9. Why did the jovian planets end up with so many moons?
The same process of heating/spinning/flattening that made solar nebula made ice-rich planetisimals in circular orbits around planet's equatorial plane
3. What do we mean by the solar nebula? What was it made of, and where did it come from?
The solar nebula is the cloud of gas from which our solar system was born when it collapsed under its own gravity. By using the compositions of the Sun, other stars, and interstellar gas clouds, we know that the solar nebula contained 98% hydrogen and helium and only 2% of all other elements combined. This came from the billion of years of galactic recycling that occurred before the Sun and planets were born.
4. Describe each of the three key processes that led the solar nebula to take the form of a spinning disk. What observational evidence supports this scenario
The solar nebula took the form of a spinning disk, instead of a sphere, because of three main processes: heating, spinning, and flattening. -Heating: means that the temperature increased as it collapsed representing energy conservation. As it shrank, the PE was converted into the KE of individual gas particles falling inward. These crashed into each other, converting their inward, falling KE into the random motions of thermal energy. The Sun formed in the center, where temperatures and densities were the highest. -Spinning: Like an ice skater, the solar nebula became faster as it shrank in radius representing conservation of angular momentum. Before the collapse, the rotation was very slow, but as it shrank, fast rotation was inevitable. It helped ensure that everything in the nebula didn't crash into the center because the greater the angular momentum, the more spread out it would be. -Flattening: consequence of collisions between particles in a spinning cloud. Randomly shaped and sized clumps of gas collide and merge as the cloud collapses and each clump gets the average velocity of the clumps that formed it. Basically, it becomes more orderly as the cloud collapses. The observational evidence supporting this scenario include the infrared radiation we've detected from many nebulae where star systems appear to be forming. Also, other stars have flattened, spinning disks. Other support comes from computer simulations. Also, we see other examples (like the Milky Way, planetary rings, and accretion disks of neutron stars and black holes) of where flattening should occur because of the orbiting particles colliding.
Our bodies (and most living things) are made mostly of water: H20. Summarize the "history" of a typical hydrogen atom from its creation to the formation of Earth. Do the same for a typical oxygen atom.
The typical hydrogen atom is first seen in the big bang, over time they clump together and begin to form compounds such as ammonia. These compounds are part of the disk, they freeze and accrete into planets. Oxygen created in the center of a star through nuclear fusion and is shot off into space. Both of them get into the disk, freeze if they're a water molecule. Free oxygen doesn't exist well anywhere besides Earth.
24. A solar system has four Earth-size terrestrial planets. Each of the four planets has a single moon that is nearly identical in size to Earth's Moon.
This is unusual because the size of our own moon relative to the size of our planet is very large. Our planet is not large enough to capture a moon our size in our gravity, therefore our moon had to have been created when an asteroid collided into Earth.
28. Radiometric dating of meteorites from another solar system shows that they are a billion years younger than rocks from the terrestrial planets of the same system.
True. They have remained unchanged since then.
23. A solar system has six terrestrial planets and four jovian planets. Each of the six terrestrial planets has at least five moons, while the jovian planets have no moons at all.
Unusual because Jovian planets have a much larger mass and lots of gas, which makes it easier for them to create moons with accretion and capture moons in their orbit
1. What are the four major features of our solar system that provide clues to how it formed? Describe each one briefly.
a. Patterns of motion among large bodies- Sun, planets, large moons rotate in an organized way (co-planar)—nearly circular orbits in the same direction (coplanar and prograde) b. Two major types of planets- terrestrial vs. jovian planets c. Asteroids and comets- locations, orbits, and compositions follow distinct patterns—Asteroids are b/t Mars and Jupiter in theasteroid belt. Also located in the Kuiper belt and Oort Cloud d. Exceptions to the rules- Earth is inner planet with large moon, Uranus is only side tilted axis, etc.
