11.2 – THE SUN AND ITS PLANETARY SYSTEMS

THE PLANETS To be a planet, 3 criteria must be

met: Must orbit one or more stars Must be large enough that its own gravity holds it in a spherical shape

Must be the only body occupying the orbital path

This distance between planets is SO large that we don’t measure in kilometres!

Astronomical Unit (AU): equal to the average distance between the Sun and Earth (about 150 million km) Earth = 1 AU from the Sun Jupiter = 5.27 AU from the Sun

1. MOONS Also known as “satellites” All planets except Mercury and

Venus have 1 or more orbiting companions

Earth’s satellite is named the Moon More than 150 moons have

recognized in our solar system

2. ASTEROIDS Small bodies believed to be

leftover remains from the formation of the solar system

Most orbit the Sun in a band between Mars and Jupiter

Can be as small as grains of sand or up to 1000km wide (ex. Ceres)

3. COMETS Composed of ice, rock, and gas Originate from the Kuiper Belt and

the Oort Cloud Can get bumped into the inner

solar system Can see a trail of gas/dust when effected by sunlight

4. TRANS-NEPTUNIAN OBJECTS Objects that circle the Sun beyond Neptune’s

orbit Kuiper Belt

A flat disk of millions of small bodies orbiting the Sun

Believed to be made of fragments of material left over from the solar system’s formation

Dwarfs planets, similar in composition/size to Pluto, orbit in this belt Believed to be 23 objects in the Kuiper Belt

that may be considered planets

5. OORT CLOUD A spherical cloud of small icy

fragments Located at the farthest reaches of

the Sun’s gravitational influence Believed to be a source of comets Roughly 50,000-100,000 AU from

the Sun