Dwarf Planets Is Pluto a Planet INTRODUCTION Important

Dwarf Planets Is Pluto a Planet?

INTRODUCTION Important dates in Pluto’s history: What you will learn: • The definition of objects in our solar system • The difference between a planet and a dwarf planet

INTRODUCTION What you will need: • Internet • Statement activity sheet • Dwarf Planet matrix sheet How would you define a: • Planet • Asteroid • Satellite (moon) • Dwarf Planet

ACTIVITY ONE What do you think of these statements and those on the following slides? Do any of them define a planet? What are they describing? Orbits a star Has at least one natural satellite (moon) Is not a satellite of another object Orbits within the inner solar system Defines a planet Does not define a planet Discuss your answers for each statement and then turn over to the next slide to see if you were right.

ACTIVITY ONE Orbits a star Defines a planet Does not define a planet Exoplanets (planets outside our solar system) orbit stars. Planets in our solar system orbit our star (the Sun) Has at least one natural satellite (moon) There is no rule about whether a planet needs a satellite, both Mercury and Venus have no moons Is not a satellite of another object Orbits within the inner solar system While a planet can not be a satellite of another object, this is not in the official definition The four gas giants (Jupiter, Saturn, Uranus and Neptune) are all outside the inner solar system, beyond the asteroid belt

ACTIVITY ONE Has sufficient mass to be round or nearly round Has signs of water (e. g. ice or vapour) A celestial body that orbits around a larger body Has an atmosphere

ACTIVITY ONE Has sufficient mass to be round or nearly round This is an important feature for defining a planet, all planets must be close to spherical Has signs of water (e. g. ice or vapour) There is no rule about whether a planet needs to have signs of water of any kind A celestial body that orbits around a larger body Has an atmosphere This defines a natural satellite (moon) not a planet There is no rule about whether a planet has an atmosphere or not, however Mercury is the only one that does not

ACTIVITY ONE A mostly rocky (or metal) surface Orbits the Sun Can only be seen through a telescope Orbits the Earth Has cleared its orbit

ACTIVITY ONE A mostly rocky (or metal) surface Orbits the Sun This defines an asteroid not a planet, planets can be rocky or gaseous This is an important feature for defining a planet, all planets must be orbiting the Sun, our star. Can only be seen through a telescope Orbits the Earth This does not define a planet, we can see Mercury, Venus, Mars, Jupiter and Saturn with our eyes most of the year Has cleared its orbit This is not a definition for a planet, only the moon and man-made satellites orbit Earth This was a key factor in the Pluto debate, a planet must have cleared its orbit of debris

ACTIVITY ONE A mostly rocky (or metal) surface Orbits the Earth Orbits the Sun Can only be seen through a telescope Has signs of water (e. g. ice or vapour) Has cleared its orbit A celestial body that orbits around a larger body Has an atmosphere Has sufficient mass to be round or nearly round Orbits a star Orbits within the inner solar system Is not a satellite of another object Has at least one natural satellite (moon)

ACTIVITY ONE IAU Definitions: (1) A “planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, and (c) has cleared the neighbourhood around its orbit. (2) A “dwarf planet” is a celestial body that (a) is in orbit around the Sun, (b) has sufficient mass for its self-gravity to overcome rigid body forces so that it assumes a hydrostatic equilibrium (nearly round) shape, (c) has not cleared the neighbourhood around its orbit, and (d) is not a satellite.

INTRODUCTION • Including Pluto we have 5 known dwarf planets in our solar system

ACTIVITY TWO • Do your own research to complete the table shown below

ASSESSMENT • Compare the answers in your dwarf planet matrix with the matrix for planets, how do they compare? Which does Pluto fit with best?

ASSESSMENT Take a vote: Should Pluto be a planet or a dwarf planet? Planet Dwarf Planet