1. 7.5 Other Objects in the Solar System
Comets, dwarf planets, meteoroids and asteroids are other important objects in the solar system
Objects that circle the Sun beyond the orbit of Neptune are called trans-Neptunian objects
They are located in the Kuiper Belt, which is a disc shaped group of millions of small objects orbiting the Sun
It is believed that the Kuiper Belt is composed of fragments of material left over from the formation of the solar system
We’ve talked about the plants and the Moon

2. Pluto The Kuiper Belt contains the former planet Pluto
Pluto is composed of rock and ice, and has 3 moons
Pluto and similar objects are referred to as dwarf planets
The largest Kuiper Belt object is Eris, has a moon
In 2006, Pluto was demoted to dwarf planet status because its orbit sometimes crosses Neptune’s orbit
Just to try and put things into perspective for you, Earth’s diameter is 12,700 km, Pluto’s is 2300 km, Eris’ is 2700 km

3. Remember: Planet: an object that orbits one or more stars (and is not a star itself), is spherical and does not share its orbit with another object
The Oort Cloud
At the farthest reaches of the Sun’s gravitational influence lies a spherical cloud of small icy fragments of debris called the Oort Cloud
It is between AU and AU from the Sun (Eris is only 100 AU!)

4. Comets Comets are composed of dust, ice and rock
Most comets originate in the Kuiper Belt and the Oort Cloud
Ever so often a comet gets close to Jupiter and Jupiter’s gravitations force will either capture the comet, or nudge the comet to change its orbit and enter the inner solar system

5. When a comet comes close to the Sun, the radiation from the Sun releases the gases and particles in the comet
The wind from the Sun pushes the gases and particles away, this forms a comet tail
The whitish tail is sunlight reflecting off the particles that have been released (debris that stays in the comet’s orbit)
The blue tail is the gases that have been ionized by the Sun’s radiation (ion tail)

6. Asteroids
Asteroids are small, non-spherical objects that are believed to be debris left over from the formation of the solar system
Most asteroids orbit the Sun in a band (asteroid belt) between Mars and Jupiter
Asteroids range in size from a tiny speck to 500 km wide
Some asteroids have been promoted to dwarf planet status -one was 1000 km wide and had its own moon

7. Other Objects Meteoroids are pieces of rock moving though space
- Believed to be pieces of asteroids and planets
When meteoroids collide with Earth’s atmosphere they burn up due to atmospheric friction forming meteors
When Earth passes through an area where there is a lot of excess material (such as debris from a comet) a meteor shower results
- AKA “shooting stars”

8. Meteoroids that survive the impact with the atmosphere and reach the ground are called meteorites
Scientists estimate that metric tonnes of material from meteorites reach Earth’s surface annually
Video Perseid Meteor Shower 3:00 min

9. Asteroid and Meteorite Impacts
An asteroid about the size of a mountain struck the Earth 65 million years ago
Resulted in catastrophic changes to Earth’s atmosphere
Widely believed it is responsible for mass extinctions including the dinosaurs
39 M years ago, 2 km wide object hit Nunavut, 20 km crater

10. Tunguska, Siberia, Russia
- In 1908, and object impacted here and destroyed an area of over 2000 km2
- Equal to the size of Essex County
- The object was probably only 50 m in diameter!
Video Meteorite in Russia 1:25 min
Homework: page 306 #1-5, 6-8