550 PART 4^ |^ THE SOLAR SYSTEM
- What is the orbital velocity of Miranda around Uranus? (Hints: See
Chapter 5, and look in the Appendix tables for Oberon’s orbital data.) - What is the escape velocity from the surface of Miranda? (Hints:
Miranda’s radius 242 km. Assume that its density is 2.00 g/cm^3.
See Chapter 5.) - The magnetosphere of Uranus rotates with the planetary interior in
17.24 hours. What is the velocity of the outer portion of the magnetic
fi eld just beyond the orbit of Oberon? (Hints: The circumference of a
circle is 2πr; look in the Appendix tables for Oberon’s orbital data.) - If the ring is 60.0 km wide and the orbital velocity of Uranus around
the sun is 6.81 km/s, how long a blink should you expect to see when
the ring crosses in front of a star? Is this consistent with the data on
page 534? - What is the escape velocity from the surface of an icy moon with a
diameter of 20 km? (Hints: The density of ice is 1 g/cm^3. The volume
of a sphere is __^43 πr^3. See Chapter 5.) - What is the difference in the orbital velocities of the two shepherd
satellites Cordelia and Ophelia? (Hints: Orbital radii 49,800 km and
53,800 km. See Chapter 5.) - Repeat Problem 2 for Pluto. In other words, ignoring the motion of
Earth, how far across the sky would Pluto move in 24 hours? (Assume a
circular orbit for Pluto.) - Given the size of Triton’s orbit (r 355,000 km) and its orbital period
(P = 5.88 days), calculate the mass of Neptune. (Hint: See Chapter 5.)
Learning to Look
- Compare Figure 24-8 with Figure 24-7 and add labels to the aurora
identifying the north and south magnetic poles on Uranus. - Sketch Earth’s moon to scale in Figure
24-11. - Two images of Uranus show it as it
would look to the eye and through a
red fi lter that enhances methane clouds
in the northern hemisphere. Why didn’t
Voyager 2 photograph the northern
hemisphere? What do the visible atmospheric features tell you about
circulation on Uranus? - If Neptune had no satellites at all, would you expect it to have rings?
Why or why not? - Why might the surface brightness of ring particles and small moons
orbiting Uranus and Neptune depend on whether those planets have
extensive and strong magnetic fi elds? - Both Uranus and Neptune have a blue-green tint when observed
through a telescope. What does that tell you about their composition? - How can small worlds like Triton and Pluto have atmospheres when a
larger world such as Ganymede has none? - Why do you suspect that Triton has had an active past? What sources
of energy could power such activity? - If you visited the surface of Pluto and found Charon as a full moon
directly overhead, where would Charon be in the sky when it was new?
When it was fi rst quarter? - What evidence can you cite that Pluto and Charon are made of
mixtures of rock and ice? - Why was Pluto reclassifi ed as a dwarf planet?
- How Do We Know? How was the discovery of Neptune not
accidental?
Discussion Questions
- Why might it be unfair to describe William Herschel’s discovery of
Uranus as accidental? Why might it be unfair to describe the discovery
of the rings of Uranus as accidental? - Suggest a single phenomenon that could explain the inclination of the
rotation axis of Uranus, the peculiar orbits of Neptune’s satellites, and
the existence of Pluto’s moons.
Problems
- What is the maximum angular diameter of Uranus as seen from Earth?
Of Neptune? Of Pluto? (Hint: Use the small-angle formula, Chapter 3.) - One way to recognize a distant planet is by its motion along its orbit.
If Uranus circles the sun in 84.0 years, how many arc seconds will it
move in 24 hours? (This does not include the motion of Earth. Assume
a circular orbit for Uranus.)
NASA