The outer solar system consists of the four gas giant planets - Jupiter, Saturn, Uranus, and Neptune. These planets are primarily made of hydrogen and helium and have no solid surface, as the immense pressure from their thick atmospheres liquefies their interiors. Their moons display a variety of compositions from rocky to icy to volcanic. Rings of dust, ice, and rock encircle the outer planets, most notably Saturn's rings. Comets are known as "dirty snowballs" composed mainly of ice and rock, and their tails form when ice sublimates from their nuclei as they near the Sun. Exploration has included long-term missions to Jupiter and Saturn, while Uranus and Neptune

1. THE OUTER
SOLAR SYSTEM
FACTS ABOUT

2. THE OUTER SOLAR
SYSTEM
▸ Include Jupiter, Saturn, Uranus, and Neptune
▸ Nearly all of planets’ mass is made up of hydrogen and helium, similar
to composition of the sun
▸ No solid surface beneath outer layers—pressure from their thick
atmospheres liquefy insides
▸ Might have rocky cores

3. THE OUTER SOLAR SYSTEM
▸ Moons of outer planets have variety of compositions ranging from rocky
to icy to volcanic
▸ Rings of dust, rock, and ice encircle outer plants—rings of Saturn most
famous

4. COMETS IN THE OUTER
SOLAR SYSTEM
▸ Known as “dirty snowballs”
▸ Consist mainly of ice and rock
How it works: When a comet’s orbit takes it close
to the sun, some of the ice in its central nucleus
turns into gas that shoots out of its sunlit side,
which the solar wind carries outward to form a long
tail.

5. COMETS IN THE OUTER SOLAR SYSTEM
▸ Short-period comets that complete their orbits in less than 200 years are
thought to originate from the Kuiper belt
▸ Long-period comets that take more than 200 years to orbit are thought to
originate from more distant Oort Cloud

6. EXPLORATION OF THE
OUTER SOLAR SYSTEM
▸ Long-term missions to Jupiter
conducted by spacecrafts Juno and
Galileo
▸ Long-term mission to Saturn
conducted by Cassini spacecraft
▸ Only fly-by missions to Uranus and
Neptune by Voyager 2 in 1980s
▸ Scientists working on Uranus or
Neptune orbiter to be conducted in
2030s

7. EXPLORATION OF OUTER SOLAR
SYSTEM
Scientists also make observations from the ground to trace long-term
changes in weather and cloud formations in the “gas giants”.

8. TEST YOURSELF
▸ List the four planets of the outer solar system
▸ Describe the physical properties characteristic of a “gas giant”— gas
composition, beneath surface, inner core
▸ True or false: Comets can take more than 200 years to complete their
orbit
▸ True or false: On-planet missions by spacecraft have been made to
Uranus and Neptune