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Uranus is a cloudy, Jovian

world far from the sun. It

is orbited by dark, rocky

particles that make up

narrow rings much

enhanced in this artist’s

impression. (Bryan

Brandenburg)

Guidepost

Two planets circle the sun in the twilight beyond Saturn. You will fi nd Uranus and

Neptune substantially different from Jupiter and Saturn but still recognizable as Jovian

planets. As you explore further you will also discover a family of dwarf planets, including

Pluto, which appear to be leftover planet construction material. This chapter will help

you answer four essential questions:

How are Uranus and Neptune similar to, and different from, Jupiter and Saturn?

How did Uranus and Neptune, along with their rings and moons, form and evolve?

How is Neptune different from Uranus?

How are Pluto and the dwarf planets related to the origin of the solar system?

As you fi nish this chapter, you will have visited all of the major worlds in our solar

system. But there is more to see. Vast numbers of small rocky and icy bodies orbit among

the planets, and the next chapter will introduce you to these fragments from the age of

planet building.

Uranus, Neptune, and

24 the Dwarf Planets