Ice Giants, Dwarf Planets, the Kuiper Belt and the Oort Cloud: Practice Problem Solutions

1. Uranus and Neptune; Voyager 2 flew by them in 1986 and 1989.

2. It spins on its side, with its axis tilted about 98 degrees.

3. They are the fastest in the solar system, up to about 2,000 km/h.

4. It orbits the Sun, is massive enough to be round, and has cleared its orbit of other objects.

5. It orbits the Sun and is round, but it has not cleared its orbit; it shares its region with many other Kuiper belt objects.

6. Beyond Neptune, from about 30 to 50 AU. Short-period comets come from it.

7. From the orbits of long-period comets, which arrive from all directions and fit a distant spherical source.