The Outer Planets

The Outer Planets — page 1 — 4 The inner solar system is home to relatively small rocky planets Mercury Venus Earth and Mars and is surrounded by the asteroid belt a ring of small rocky objects The inner solar system is tiny compared to the vast expanse of the outer solar system and the rocky planets are also tiny compared to their outer neighbors We’ll be visiting the giant outer worlds Jupiter Saturn Uranus and Neptune each of which is dominated by gas and ice rather than rock The Sun is an enormous ball of exploding gas much larger than any planet Like all heavy objects it produces a pull called gravity This pull stops fast-moving objects from ﬂying off into space and instead traps them in circular or oval paths called orbits INNER AND OUTER SOLAR SYSTEM SOLAR SYSTEM CENTER Get ready to blast off on the trip of a lifetime We’re going exploring into cold dark and dangerous territory to the outer reaches of the solar system The solar system consists of our nearest star the Sun and everything that circles around it The Outer Solar System URANUS 19 2 AU FROM SUN NEPTUNE 30 1 AU FROM SUN SATURN 9 5 AU FROM SUN JUPITER 5 2 AU FROM SUN

The Outer Planets — page 2 — 5 NEED TO KNOW Each giant planet has its own large family of moons in orbit around it and we’ll also be visiting many of these as we go We will then ﬁnish our trip with a visit to the comets and dwarf planets small icy astronomical bodies that hang at the very edge of our solar system Along the way we’ll learn about the unique histories features and hazards of these fascinating objects It’s going to be a fun trip but be careful it could also be a dangerous one MOONS AND OTHER BODIES It’s a long trip to the outer solar system The Earth is 93 million miles 150 million km from the Sun this is one astronomical unit or AU but the outer planets are much farther away The distances from the Sun are as follows Jupiter 5 2 AU Saturn 9 5 AU Uranus 19 2 AU Neptune 30 1 AU The dwarf planet Pluto see page 28 is 39 5 AU and the farthest point of the collection of icy objects known as the Kuiper belt see page 29 is about 47 AU MARS 1 5 AU FROM SUN EARTH 1 AU FROM SUN MERCURY 0 4 AU FROM SUN VENUS 0 7 AU FROM SUN ASTEROID BELT 2 8 AU FROM SUN EARTH’S MOON 238,855 MILES 384,400 KM FROM EARTH

The Outer Planets — page 3 — Named after the Roman king of the gods Jupiter is the largest planet in the solar system Earth which has a mass of 5 97 trillion trillion kilograms could ﬁt inside this vast multi-colored ball of gas 1,300 times over Some of Jupiter’s individual storms are so large they could swallow up our entire planet Jupiter D i a m et er 88,846 miles 142,984 km M a s s 3 1 8 x E a r t h D a y 9 9 h o u r s Y e a r 1 1 8 8 E a r t h y e a r s Jupiter’s Great Red Spot is large enough to contain three planets the size of Earth This huge high-pressure storm rotates counterclockwise every six or seven days and its shape color and size change constantly Jupiter pumps out a huge amount of heat and this drives powerful weather systems These are stretched out into bands that wrap around the planet giving Jupiter a striped appearance Bands of pale high-altitude clouds have gaps between them revealing dark belts lower in the atmosphere Huge storms create swirling reddish clouds The most famous of these storms the Great Red Spot has raged for more than 300 years TURBULENT WORLD 6

The Outer Planets — page 4 — 7 HAPPY FAMILY Jupiter has a huge family of 63 moons Many have stretched or tilted orbits indicating that they are asteroids that have been captured by Jupiter’s strong gravity MAJOR MOONS The four major moons Io Europa Ganymede and Callisto are collectively known as the Galilean moons after the Italian astronomer Galileo who discovered them in 1609 1610 TROJAN ASTEROIDS Jupiter shares its orbit with two large clouds of asteroids called Trojans RINGS Jupiter has its own set of planetary rings see below but they are much paler than those around Saturn see pages 16 17 GIANT OF THE SOLAR SYSTEM Jupiter is a gas giant a world very different from solid rocky planets like Earth It is made up of light gases that have collected around a roughly Earth-sized rocky core These gases make up an atmosphere hundreds of miles deep Despite the name gas giant most of Jupiter’s interior is actually liquid inside the planet the weight of gas pressing down from above squeezes the gas into a liquid Around the core is a swirling sea of liquid hydrogen that conducts electricity and generates Jupiter’s huge magnetic ﬁeld not the place for a relaxing swim The narrow planetary rings that surround Jupiter are made up of dust-sized rock particles NOT TO MISS

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