Chapter 6
The dwarf planet Eris was discovered in 2005, orbiting the Sun at an average distance about twice that of Pluto. In which of the following ways do Pluto and Eris differ from the terrestrial and jovian planets in our solar system?
1. Both Pluto and Eris are smaller than any of the terrestrial planets. 2. Both Pluto and Eris travel in more elliptical orbits than any of the terrestrial or jovian planets. 3. Both Pluto and Eris are less massive than any of the terrestrial or jovian planets.
Now consider the second major characteristic (two types of planets). Which of the following statements are true?
1. Jovian planets have more moons than terrestrial planets. 2. Jovian planets are larger in size than terrestrial planets. 3. Jovian planets are larger in mass than terrestrial planets. 4. Jovian planets orbit farther from the Sun than terrestrial planets. Knowing these basic differences between terrestrial and jovian planets in our solar system, we can look to see whether the same categories of planets are found in other solar systems.
Study the features relating to the first characteristic (orderly motions); click on the inner or outer solar system to see the planets in motion, then scroll over the planets to see diagrams of their axis tilts. Which of the following correctly describe patterns of motion in the solar system?
1. Planets closer to the Sun move around their orbits at higher speed than planets farther from the Sun. 2. All the planets (not counting Pluto) orbit the Sun in nearly the same plane. 3. All the planets (not counting Pluto) have nearly circular orbits.
All the following statements are true. Which of them are considered to be "exceptions" to the general trends described by the first three major characteristics of the solar system?
1. Uranus rotates with an axis tilt that lies nearly in the ecliptic plane. 2. Venus rotates in a direction opposite to the rotation of the other terrestrial planets. 3. Our Moon has a diameter more than 1/4 the diameter of Earth. Note that these exceptions must still be accounted for by any reasonable theory of solar system formation.
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 __________.
1. the asteroid belt 2. the Oort cloud 3. the Kuiper belt Most asteroids are found in the asteroid belt between Mars and Jupiter. Comets are found in two regions: the Kuiper belt just beyond the orbit of Neptune and the much more distant and spherically shaped region known as the Oort cloud.
You are dating rocks by their proportions of parent isotope potassium-40 (half-life 1.25 billion years) and daughter isotope argon-40. Find the age for each of the following. Part A: A rock that contains equal amounts of potassium-40 and argon-40. Part B: A rock that contains 31 times as much argon-40 as potassium-40.
A. t = 1.25 x 10^9 years B. t = 6.25 x 10^9 years
The following images show four planets in our solar system. Rank these planets from left to right based on the number of moons that orbit them, from highest to lowest. (Not to scale.)
Jupiter, Mars, Earth, Mercury Jupiter has many moons as a consequence of its formation, in which moons formed in a disk of material surrounding it and its extended atmosphere at the time allowed it to capture numerous small bodies into orbit. Mars has two very small moons that it presumably captured at a time when it, too, had an extended atmosphere. Earth's single but surprisingly large moon is thought to have formed as a result of a giant impact. Mercury (and Venus) have no moons.
The following images show five planets in our solar system. Rank these planets from left to right based on their average surface (or cloud-top) temperature, from highest to lowest. (Not to scale.)
Mercury, Earth, Mars, Jupiter, Neptune 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.
The following images show five planets in our solar system. Rank these planets from left to right based on the amount of time it takes them to orbit the Sun, from longest to shortest. (Not to scale.)`
Neptune, Jupiter, Mars, Earth, Mercury Recall that the time it takes a planet to orbit the Sun is called its orbital period, and that Kepler's third law tells us that orbital period increases with distance from the Sun. That is why the ranking order for orbital period is the same as the ranking order for distance from the Sun.
The following images show six objects in our solar system. Rank the objects from left to right based on their average distance from the Sun, from farthest to closest. (Not to scale.)
Pluto, Saturn, Jupiter, Mars, Earth, Mercury
The following images show six objects in our solar system. Rank these objects from left to right based on their mass, from highest to lowest. (Not to scale.)
Sun, Jupiter, Earth, Mars, Mercury, Pluto
The images below show six objects in our solar system. Rank these objects by size (average equatorial radius), from largest to smallest. (Not to scale.)
Sun, Jupiter, Earth, Mars, Mercury, Pluto
Listed following are statements that, based on their current theory of solar system formation, apply either to the formation of terrestrial planets or of jovian plantets, but not both. Match these to the appropriate category.
Terrestrial Planets: -- accreted from planetismals of rock and metal -- surfaces dramatically altered during the heavy bombardment Jovian Planets: -- formed in regions cold enough for water to freeze -- large moons formed in surrounding disks of material -- formed in a region of the solar system with lower orbital speeds --accreted from icy planetismals -- ejected icy planetismals that are now Oort cloud comets
Assuming that other planetary systems form in the same way as our solar system formed, where would you expect to find terrestrial planets?
Terrestrial planets will likely be located nearer the planetary system's star than any jovian planets. Based on what we find in our own solar system, we expect terrestrial planets to form close to a star and jovian planets to form farther out.
Consider only the observed patterns of motion in the solar system. Scientifically, which of the following possible conclusions is justified from the patterns of motion alone?
The planets were not each born in a separate, random event.
Based on your study of the interactive figure, which of the following is not one of the four major features of the solar system?
The solar system contains eight planets plus dwarf planets (including 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.
Which planet is approximately halfway between Pluto's orbit and the Sun?
Uranus, the seventh planet from the Sun Notice that Uranus is located at an average distance of 19.2 AU, which is close to half of Pluto's average distance of 39.5 AU. Many people are surprised to realize that Uranus, the seventh planet from the Sun, is only half as far as Pluto. As you can see in the figure, this surprising fact arises because the outer planets are much more widely spaced than the inner planets.
Where would you expect terrestrial planets to form in the solar nebula?
anywhere between 0.3 AU and the frost line Terrestrial planets are made mostly of metal and rock and therefore formed in the region in which it was cool enough for metal and rock to condense but still too warm for hydrogen compounds to condense into ices. This means the region between the rock/metal condensation line at 0.3 AU and the frost line.
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 __________.
make testable predictions about 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.
Compared to terrestrial planets, jovian planets are __________.
more massive and lower in average density Note that while jovian planets are lower in average density than terrestrial planets, the densities in their deep interiors are quite high, in some cases higher than the densities found at the centers of the terrestrial worlds.
What substances existed as solid flakes within the inner 0.3 AU of the solar system before planets began to form?
none Although all the materials were present in gaseous form, the inner 0.3 AU of the newly forming solar system was too warm for even rocks or metals to condense into solid flakes.
Now 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 __________.
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.
The jovian planets are thought to have formed as gravity drew hydrogen and helium gas around planetismals made of _________.
rocks, metals, and ices Because ices could condense only beyond the frost line, we expect jovian planets to form only beyond the frost line. Note that many extrasolar planets appear to be jovian but are located close to their stars, leading scientists to suspect that these planets migrated inward after originally forming beyond the frost lines of their star systems.
What substances were found within the inner 0.3 AU of the solar system before planets began to form?
rocks, metals, hydrogen compounds, hydrogen, and helium, all in gaseous form All the materials of the solar nebula were present in the inner region, but it was too hot for any of them to condense. As a result, they were all in gaseous form.