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

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

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 50 000 AU and 100 000 AU from the Sun (Eris is only 100 AU!)

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

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)

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

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”

Meteoroids that survive the impact with the atmosphere and reach the ground are called meteorites Scientists estimate that 100 000 metric tonnes of material from meteorites reach Earth’s surface annually Video http://www.youtube.com/watch?v=vroLnrBhbmk Perseid Meteor Shower 3:00 min

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

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 http://www.youtube.com/watch?v=90Omh7_I8vI Meteorite in Russia 1:25 min Homework: page 306 #1-5, 6-8