The Cosmic Perspective - Module #8 (Homework)

What are the features of a Terrestrial Planet?

Answer: - Small Size - Solid; Rocky Surface - Located within the Inner Solar System

For the purposes of seeking a theory to explain the formation of the solar system, we identify four major features of our solar system. What would you say represents these four major features?

Answer: - Swarms of asteroids and comets populate the solar system. - Several exceptions to the general trends stand out. - Large bodies in the solar system have orderly motions. - Planets fall into two major categories (terrestrial and Jovian).

The solar system contains vast numbers of small bodies, which we call asteroids when they are rocky and comets when they are icy. These small bodies are concentrated in the region(s) of the solar system that we call __________.

Answer: - The Asteroid Belt - The Kuiper Belt - The Oort Cloud (Most asteroids are found in the asteroid belt between Mars and Jupiter. Comets are concentrated in two regions: the Kuiper belt just beyond the orbit of Neptune and the much more distant and roughly spherical region known as the Oort cloud.)

What is Neptune's largest moon?

Answer: Triton. (Neptune's largest moon is Triton and is said to have once orbited the Sun independently.)

On average, Venus is the hottest planet in the solar system - even hotter than Mercury. True or False?

Answer: True (The average temperature of Venus is 740 Kelvin. Mercury's temperature is about 700 Kelvin during the day and 100 Kelvin in the night.)

The planet with the highest average surface temperature in the universe is _______________.

Answer: Venus

Did Mars used to have surface liquid on it's planet's surface in the distant past?

Answer: Yes, Mars did have surface liquid in it's distant past but it has long disappeared as of today.

Does Mercury's day and night time vary exponentially?

Answer: Yes, Mercury's day and night cycle are the most distinguished out of all the planets in the solar system.

Does Uranus experience very extreme seasons?

Answer: Yes, Uranus experiences extreme seasons because of its axis tilt.

Is Venus's surface hot enough to melt lead?

Answer: Yes, Venus's surface is hot enough to melt lead which is in part due to an extremely strong greenhouse effect.

What is the Kuiper belt?

Answer: a region of the solar system beginning just beyond the orbit of Neptune that contains many icy comets (Pluto and Eris are both members of the Kuiper belt.)

The solar nebula was 98 % ...

Answer: hydrogen and helium.

According to our theory of solar system formation, what are asteroids and comets?

Answer: leftover planetesimals that never accreted into planets.

The "giant impact hypothesis" refers to the idea that ______________.

Answer: our Moon formed when a Mars-size object collided with the young Earth.

In essence, the nebular theory holds that __________.

Answer: our solar system formed from the collapse of an interstellar cloud of gas and dust.

The nebular theory holds that:

Answer: our solar system formed from the collapse of an interstellar cloud of gas and dust.

The most abundant ingredient of the Sun and Jupiter is:

Answer: Hydrogen

Rank these planets from left to right based on their average surface (or cloud-top) temperature, from highest to lowest. - Earth - Neptune - Jupiter - Mercury - Mars

Answer: - Mercury (Highest Average Surface Temperature) - Earth - Mars - Jupiter - Neptune (Lowest Average Surface Temperature) (Notice that, for these five planets, temperature correlates with distance from the Sun: the closer to the Sun, the hotter the planet. Remember, however, that this is not always the case, because a planet's temperature also depends on its reflectivity and on the strength of its greenhouse effect (if any). For example, the greenhouse effect gives Venus a higher average temperature than Mercury, even though Venus is nearly twice as far from the Sun.)

Consider the second major feature (two types of planets). Which of the following statements are true for the terrestrial and Jovian planets in our solar system?

Answer: - Jovian planets orbit farther from the Sun than terrestrial planets. - Jovian planets are larger in mass than terrestrial planets. - Jovian planets have more moons than terrestrial planets. - Jovian planets are larger in size than terrestrial planets. (Note that the characteristics relating to size, mass, and composition are considered to be defining characteristics for the terrestrial and Jovian categories; that is, we would identify planets in other systems as terrestrial or Jovian if they have these same general characteristics. In contrast, while all the Jovian planets in our solar system orbit much farther from the Sun than the terrestrial planets, there are other solar systems in which Jovian planets have been found to orbit much closer to their stars.)

Based on the nebular theory as it explains our own solar system, What should we expect to be true for other star systems?

Answer: - Many extrasolar planets should fall into the terrestrial or Jovian categories. - Planetary systems should be common. - Planetary systems should generally have all planets orbiting in nearly the same plane. - Jovian planets always form farther from their star than terrestrial planets. (We expect all solar systems to form in similar ways from collapsing gas clouds and therefore to share basic features, such as the planets all orbiting in the same direction and nearly the same plane. We also expect planets to form similarly through accretion, with planets that form near a star tending to be terrestrial in nature and planets that form farther away tending to be jovian; however, as you'll learn in later chapters, the details of planetary formation allow for additional types of planets beyond just those two categories. We do not expect particulars that are probably coincidental, such as the precise numbers of planets, to be the same in different solar systems.)

What characteristics support "Giant Impact Hypothesis".

Answer: - Models indicate that an early Solar System had Mars-size leftover planetesimals. - The Moon's composition is similar to Earth's mantle. - The Moon has a low proportion of easily vaporized ingredients.

What are considered to be "exceptions" to the general trends described by the first three major features of the solar system?

Answer: - Our Moon has a diameter more than 1/4 the diameter of Earth. - Uranus rotates with an axis tilt that lies nearly in the ecliptic plane. - Venus rotates in a direction opposite to the rotation of the other terrestrial planets. (Note that these exceptions must still be accounted for by any reasonable theory of solar system formation.)

What are four key features of our solar system that any theory of solar system formation must be able to explain?

Answer: - Planets fall into two major categories. - There are a few notable "exceptions to the rules." - There are clear patterns to the rotation and orbits of large bodies in the solar system. - There are vast numbers of asteroids and comets.

Consider the first major feature (orderly motions). Which of the following correctly describe patterns of motion in our solar system?

Answer: - Planets have nearly circular orbits. - All the planets orbit the Sun in nearly the same plane. - The Sun and most of the planets rotate in the same direction that the planets orbit. (Be sure to note that while the Sun and most planets rotate in the same direction that the planets orbit, there are two notable exceptions: Venus and Uranus. Also note that most major moons orbit in this same direction and in a planet near that of their planet's equator (which means they are not in polar orbits.)

What are the features of a Jovian Planet?

Answer: - Primarily composed of Hydrogen, Helium, and Hydrogen Compounds. - Numerous Orbiting Moons. - Extensive Ring Systems. - Low Average Density.

Consider a radioactive substance with a half-life of 10 years. If you start with 1 kilogram of this substance, after 20 years, _____ of the radioactive substance will remain.

Answer: 0.25 kilogram (After 10 years, half of the original amount will remain. After 20 years half of that half, or 1/4 of the original amount, will remain.)

Suppose you have a rock that, when it solidifies, contains 1 microgram of a radioactive isotope. How much of this isotope remains after five half-lives?

Answer: 1/32 Microgram

Suppose you find a rock and measure that 12.5% of the original uranium-235 still remains it, while the other 87.5% has decayed into lead-207. About how old is the rock?

Answer: 2.1 Billion Years

According to modern scientific dating techniques, approximately how long ago did Earth and the other planets of our solar system form?

Answer: 4.5 billion years

Approximately what is the half-life of uranium-235?

Answer: 700 Million Years (The answer is found simply by looking at the point on the graph where half of the uranium-235 has decayed into lead-207. This point, which is labeled "1 half-life," is found at a position corresponding to about 0.7 on the horizontal axis, which means 0.7 billion, or 700 million, years.)

According to modern science, what was the approximate chemical composition of the solar nebula?

Answer: 98% hydrogen and helium, 2% everything else.

What is Eiris?

Answer: A Dwarf Planet that is similar in size to Pluto.

The spacecraft called Curiosity is _____________.

Answer: A rover on Mars.

When did the objects that we now see as asteroids and comets form in the solar system?

Answer: After solid particles condensed from the gas but before the planets finished forming. (Asteroids and comets are leftover planetesimals, and as shown in the video, planetesimals formed through the accretion of the solid particles that condensed from the nebula.)

Which Jovian planets in our solar system have rings?

Answer: All Jovian planets have rings. (All four Jovian planets have rings, although Saturn's rings are the only ones easily visible from Earth.)

How many of the planets orbit the Sun in the same direction that Earth does?

Answer: All of them.

Suppose you view the solar system from high above Earth's North Pole. Which of the following statements about planetary orbits will be true?

Answer: All the planets orbit counterclockwise around the Sun. (This is a consequence of the way the planets formed in a spinning disk around the young Sun.)

As you've seen, the nebular theory predicts that a cloud that gives birth to planets should have the shape of a spinning disk. Which observable property of our solar system supports this prediction?

Answer: All the planets orbit the Sun in the same direction and in nearly the same plane. (The orbits of the planets reflect the rotation pattern of the flat, rotating disk in which they formed.)

According to our basic scenario of solar system formation, why do the Jovian planets have numerous large moons?

Answer: As the growing Jovian planets captured gas from the solar nebula, the gas formed swirling disks around them, and moons formed from condensation accretion within these disks.

Which of the following most clearly distinguishes asteroids and comets from planets?

Answer: Asteroids and comets are much smaller than planets. (Asteroids and comets together are classified as "small bodies" in the solar system, and even the largest are much smaller than Mercury.)

According to the nebular theory of solar system formation, why were solid planetesimals able to grow larger in the outer solar system than in the inner solar system?

Answer: Because only metal and rock could condense in the inner solar system, whereas ice also condensed in the outer solar system.

When we say that Jovian planets contain significant amounts of hydrogen compounds except, we mean all the following chemicals except _____.

Answer: Carbon Dioxide. (Carbon dioxide contains only carbon and oxygen; it does not contain any hydrogen.)

Which lists the major steps of solar system formation in the correct order?

Answer: Collapse, Condensation, Accretion.

The nebular theory also predicts that the cloud will flatten into a disk as it shrinks in size. Which of the following best explains why the collapsing cloud should form a disk?

Answer: Colliding cloud particles exchange angular momentum and, on average, end up with the rotation pattern for the cloud as a whole. (Particles in the collapsing cloud inevitably collide with one another. These collisions allow particles to exchange angular momentum, but their total angular momentum must be conserved. Therefore, many collisions result in an averaging out of the angular momentums of individual cloud particles, a process that brings their orbits into approximately the same plane.)

The largest Terrestrial Planet and Jovian Planet are _______________ and ____________.

Answer: Earth and Jupiter.

Which of the following types of robotic mission to a planet is generally the cheapest? (Assume that the spacecraft destination is the same in all cases.)

Answer: Flyby (A flyby requires much less fuel, because it does not need to change trajectory to enter orbit, and therefore is generally the cheapest option. However, this also means that data can be collected only for the short time period of the flyby.)

Today, scientists have a theory (the nebular theory) that explains all the major characteristics of the solar system. In science, we expect a theory like this not only to explain the observed characteristics of our solar system but also to predict _____________.

Answer: General characteristics of other solar systems. (A scientific theory must always make testable predictions, because that is the only way we can evaluate the validity of the theory. In the case of a solar system theory, it should successfully explain the general characteristics of other solar systems.)

Which of the following statements was true beyond the frost line (but not interior to it)?

Answer: Giant Impacts. (Giant impacts probably explain most of the exceptions, including the existence of our surprisingly large Moon and the axis tilt of Uranus.)

Which of the following types of material can condense into what we call ice at low temperatures?

Answer: Hydrogen Compounds. (Hydrogen compounds such as water, ammonia, and methane are gaseous at high temperature but condense into ice at low temperature.)

According to our present theory of solar system formation, which of the following lists the major ingredients of the solar nebula in order from the most abundant to the least abundant?

Answer: Hydrogen and Helium gas; Hydrogen Compounds; Rock; Metal. (Hydrogen and helium gas were the most abundant by far, comprising about 98% of the solar nebula.)

The solar system has two types of planets, terrestrial and Jovian. According to the nebular theory, why did terrestrial planets form in the inner solar system and Jovian planets in the outer solar system?

Answer: Ices condensed only in the outer solar system, where some icy planetesimals grew large enough to attract gas from the nebula, while only metal and rock condensed in the inner solar system, making terrestrial planets. (Only metal and rock could condense at the high temperature of the inner solar system, so the inner planets were built by the accretion of metal and rock. Farther out, ices could also condense, leading to the accretion of ice-rich planetesimals. Some of these grew large enough for their gravity to attract gas from the solar nebula and become Jovian planets.)

What is the leading hypothesis for the origin of the Moon?

Answer: It formed from the material ejected from Earth in a giant impact.

According to our theory of solar system formation, what three major changes occurred in the solar nebula as it shrank in size?

Answer: It got hotter, its rate of rotation increased, and it flattened into a disk.

Which of the following statements about Pluto is true?

Answer: It has more in common with other icy objects in the Kuiper belt than it does with the Jovian planets (Jupiter, Saturn, Uranus, Neptune).

What is the Oort cloud?

Answer: It's not really a cloud at all, but rather refers to the trillion or so comets thought to orbit the Sun at great distances.

The Jovian planets in our solar system are __________.

Answer: Jupiter, Saturn, Uranus, Neptune. (Jovian planets are much larger than the terrestrial planets.)

We expect a scientific theory to be able to make predictions that can be tested. Which of the following is a prediction of the nebular theory that has been verified by observations?

Answer: Many stars should have planets. (The nebular theory explains planetary formation as a natural part of the star formation process, and therefore predicts that planets should be fairly common around other stars. This prediction was made long before we ever discovered such planets, so the fact that planets are indeed common is a tremendous predictive success for the nebular theory.)

Which of the following lists the planets of our solar system in the correct order from closest to farthest from the Sun?

Answer: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune

The terrestrial planets in our solar system are ______________.

Answer: Mercury, Venus, Earth, and Mars

What planet was studied up close in 2015 by the New Horizons Spacecraft?

Answer: Pluto.

In the context of studying major bodies of our solar system, what category of object does our Moon best fit?

Answer: Terrestrial World (We consider the Moon to be one of the terrestrial worlds because of its similarity in size, mass, and composition to the other terrestrial worlds (Mercury, Venus, Earth, and Mars). As you will see when we study comparative planetology, this categorization is useful for understanding geological processes on the terrestrial worlds.)

What famous storm in seen on Jupiter?

Answer: The Great Red Spot

What is the giant impact hypothesis for the origin of the Moon?

Answer: The Moon formed from material blasted out of the Earth's mantle and crust by the impact of a Mars-size object.

What type of energy does the Sun generate in it's core?

Answer: The Sun's energy is created through the fusion of Hydrogen into Helium.

How would you sum up the time it takes for planets to orbit the Sun?

Answer: The further a planet is from the Sun, the longer it takes to orbit it, whereas the closer it is the Sun, the faster it orbits it.

The nebular theory also predicts that the cloud should heat up as it collapses. What physical law explains why it heats up?

Answer: The law of conservation of energy (The law of conservation of energy tells us that energy must always be conserved. Because the cloud has much more gravitational potential energy when it is large in size than when it is small, its gravitational potential energy must be transformed into other forms of energy, such as heat (thermal energy), as it shrinks in size.)

What do we mean when we say that a nucleus undergoes radioactive decay?

Answer: The number of protons or neutrons (or both) in the nucleus changes. (Radioactive decay can happen in many different ways, but in all cases involves a change in the number of protons or the number of neutrons, or both, in the nucleus.)

Consider only the first major feature, which concerns observed patterns of motion in the solar system. Scientifically, which of the following possible conclusions is justified from the patterns of motion alone?

Answer: The planets were not each born in a separate, random event.

Which one of the following is not one of the four major features of the solar system?

Answer: The solar system contains eight planets plus dwarf planets (such as Ceres, Pluto, and Eris). (The precise number of planets is not thought to be of any particular significance, and the division between "planets" and "dwarf planets" is a recent classification scheme that does not affect the basic ideas in the four major features. That is, for the purposes of the four major features, the dwarf planets are considered to be equivalent to large asteroids or comets.)

The terrestrial planets are made almost entirely of elements heavier than hydrogen and helium. According to modern science, where did the elements heavier than hydrogen and helium come from?

Answer: They were produced by stars that lived and died before our solar system was born.

What two geologically active moon's orbit Saturn?

Answer: Titan and Enceladus.

Consider why the observed patterns of motion lead to the conclusion that the planets were not born in separate, random events. The reason for this conclusion is that, if the planets had been born in separate, random events, we would expect that ________________.

Answer: planetary orbits would have many different orientations and directions, rather than all being in the same direction and in the same plane (In science, we form hypotheses to explain something, then use the hypotheses to make predictions that we can test. In this case, we have two alternate hypotheses: random births or birth from a single cloud of gas. The hypothesis of random births predicts random orbits, which does not agree with reality and therefore has been discarded. The hypothesis of birth from a single cloud predicts patterns of motion that match those we observe; this match of prediction and observation provides evidence in favor of the hypothesis.)

Which moons of our solar system are sometimes called the Galilean moons?

Answer: the four largest moons of Jupiter: Io, Europa, Ganymede, and Calisto. (These four moons were discovered by Galileo, and their discovery played an important role in helping overturn the ancient belief in an Earth-centered universe.)

What do we mean by accretion in the context of planet formation?

Answer: the growth of planetesimals from smaller solid particles that collided and stuck together. (At first, accretion probably arose from electrostatic attractions, but as planetesimals grew larger their gravity allowed them to accrete more efficiently (as long as they didn't suffer collisions with similar-size planetesimals.)

Observations show that interstellar clouds can have almost any shape and, if they are rotating at all, their rotation is not perceptible. However, the nebular theory predicts that a cloud will rotate rapidly once it shrinks to a relatively small size. What physical law explains why a collapsed cloud will rotate rapidly?

Answer: the law of conservation of angular momentum (The law of conservation of angular momentum holds that the cloud's total angular momentum should stay unchanged as it shrinks in size. Like a spinning ice skater bringing in her arms, the cloud's rotation speed therefore increases as it shrinks. More technically, recall that angular momentum is proportional to velocity times radius; therefore, as the radius shrinks, the velocity of rotation must increase in order to keep the product of velocity times radius unchanged.)

In the context of the formation of planets in the solar nebula, the frost line marks the distance from the Sun beyond which ______________.

Answer: the temperature was low enough for hydrogen compounds to condense into ices. (Therefore, planetesimals were built only of metal and rock within the frost line, but beyond the frost line they included ices along with metal and rock.)

Use the data in the table below to choose the correct description how escape velocity is related to properties of planets. Is the trend what you expect based on what you learned about escape velocity?

Escape velocity increases with the increasing mass of the planet. Such a trend is expected because escape velocity increases with increasing mass.