Pg. 394 12.4 CYU Suggested Answers:
1. Student answers will vary. A possible answer could be, “My Very Eccentric Mother Jilted Several Newcomers.”
2. The first four planets are called terrestrial planets because they most resemble Earth in size and composition. They are also called inner planets because they are closest to the Sun.
4. Earth is unique in the solar system in that the atmosphere contains nitrogen, oxygen, and water vapour, which help maintain a moderate temperature range. The atmosphere also contains ozone, which keeps much of the harmful radiation from damaging organisms on the surface of Earth. Seventy percent of Earth’s surface is covered in water. Rich soils allow plant life to grow and adapt. Essentially, all these characteristics make Earth an ideal home for life as we know it. These characteristics are not seen on any of the other planets.
5. Mercury is the only planet with no atmosphere.
6. The presence of an atmosphere significantly affects the conditions and features on the surface of a planet. Fewer forms of cosmic radiation reach the surface, temperature ranges are moderated (the extremes are less exaggerated when an atmosphere is present), and there are generally fewer craters on the surface since smaller meteoroids are burned up in an atmosphere.
7. Earth has very few craters because 70 % of its surface is covered in water. As a result, most meteorites land in the oceans without leaving the telltale mark of a crater.
8. Mercury has a much colder nighttime temperature than Earth, despite being the closest planet to the Sun, because Mercury does not have an atmosphere to trap the heat absorbed by the planet’s surface during the day.
9. Scientists believe that life may have existed on Mars because there is evidence of glaciers and floods—water that may have supported life in the past.
10. Astronomers noted that the orbit of Uranus was irregular, as if it were being tugged by the gravitational force of another object. They used calculations to determine where the other object might be and then discovered the position of Neptune using those calculations.
11. One effect of Earth’s magnetic field is the auroras (borealis and australis), swirls of light caused by the interaction of charged particles from space with molecules of our atmosphere.
12. (a) The aurora on one of Saturn’s poles are visible.
(b) The magnetic field surrounding Saturn causes the aurora.
13. A theory that would explain the unique direction of Uranus’ rotation might be that a large object collided with Uranus early in its formation, changing the direction of its rotation. Over time, the materials of this object and the impact crater left behind would have been incorporated into the planet’s crust.
14. The three main categories of trans-Neptunian objects are planetoids, the Kuiper Belt, and the Oort Cloud. Planetoids are dwarf or minor planets, natural satellites, and minor bodies. Pluto, once considered a planet, is now a dwarf planet. The Kuiper Belt is a disk-shaped collection of thousands of small, icy bodies located between Neptune and Pluto. The Oort Cloud is located in a region just inside the place where the Sun’s physical and gravitational influence ends and is described as a spherical swarm of icy bodies.
15. Student answers will vary but should reflect distances on Figure 11. Uranus is twice as far from the Sun as Saturn. Uranus is 19 times farther from the Sun than Earth. Jupiter is slightly more than seven times as far from the Sun as Venus.
16. Gas giants have more moons than the terrestrial planets because they have significantly more mass and are therefore able to trap more debris and objects, which form moons, with their greater gravitational fields.
18. There is a relationship between a planet’s density and its distance to the Sun. The outer planets all have low densities, as it is believed that less dense gases from our early Sun were blown to the outer regions of our solar system by the force of a nearby supernova. The more dense, rocky materials that remained eventually formed the more dense, inner planets. It is important to note that the debate regarding the classification of planets is far from over.
19. (a) Criteria to distinguish terrestrial planets from the gas giants include density, distance from the Sun (which side of the asteroid belt they may be found on), mass, average diameter, number of moons, and orbital period.
(b) Two properties of planets that relate to distance from the Sun are orbital period and density. The orbital period increases with distance from the Sun, and the density decreases with distance from the Sun.