CONTENTS WHAT IS A DWARF PLANET 4 THE KUIPER BELT 8 PLUTO 10 ERIS 14 HAUMEA 18 MAKEMAKE 22 CERES 24 NEW FRONTIERS OF EXPLORATION 28 GLOSSARY 30 FOR MORE INFORMATION 31 INDEX 32
4 WHAT IS A DWARF PLANET In 1930 an American astronomer named Clyde Tombaugh noticed something unusual while looking through a tele scope He thought it was a new planet and other scientists agreed The scientists named it Pluto It was considered the smallest planet in the solar system until 2006 In 2006 a group of astrono mers decided that the definition of planet did not apply to Pluto It is now considered a dwarf planet Like planets dwarf planets are large roundish objects that orbit or travel Clyde Tombaugh took this photograph of Pluto shown with an arrow in 1930
5 Gravity is a pulling force between any two objects that works across space The greater the mass of an object the greater is its force of gravity For example the sun which has a very large mass has a great force of gravity Even a speck of dust has a force of gravity But its gravity is very very small VOCABULARY around the sun or other stars Both planets and dwarf planets have gravity The gravity of planets is strong enough to clear their orbits of smaller objects by attracting the objects to them The gravity of dwarf planets is weaker Pluto was one of the names ancient Romans used for their god of the underworld
