Our Solar System

Planets• An object that orbits one or more stars

and is not a star itself

• Spherical

• Does not share its orbit with another object

• Inner planets (Terrestrial planets) are Mercury, Venus, Earth, and Mars)

• Outer planets (Gas planets) are Jupiter, Saturn, Uranus and Neptune.

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Mercury

Venus

Earth

Mars

Jupiter

Saturn

Uranus

Neptune

ORDER OF THE PLANETS

Planetary Motion• Venus and Mercury stay near the Sun and

can only be seen in the early morning or early evening.

• Mars, Jupiter and Saturn move westward along with the fixed stars due to Earth’s rotation.

• Retrograde motion happens when Earth catches up with and passes an outer planet in its orbit. It appears that the planet makes a looping motion in the sky.

Distances Between Planets

• Planets lie so far apart that using kilometers to measure it, is not meaningful.

• Astronomers use astronomical unit (AU), which is equal to the distance between Earth and the Sun (150million km)

• The average distance between the Sun and an object that is orbiting it is called the orbital radius.

Mercury

• Craters, rocky• Small (only a bit

larger than our moon)

• No atmosphere so large temperature differences between day and night

• No moons

Venus• Size and composition similar

to Earth• Shrouded in thick clouds• Constantly rains sulfuric acid

(acid rain)

• Atmosphere contains CO2

and nitrogen.• Some areas that are flat,

volcanoes, cracks called rifts.• Hot because the atmosphere

traps the heat.• No moons

Earth• Only planet that has

life (so far)• Lots of water• Atmosphere:

nitrogen, oxygen and water vapor mainly.

• Surface is constantly changing.

• 1 moon

Mars• Red because the iron

in the rock• Volcano 3 times larger

than Mt Everest• Very deep canyon

(8km deep)• Strong winds• 2 polar ice caps• Thin atmosphere

made mainly of CO2

• 2 moons

Jupiter• Largest• Great Red Spot: a storm

of hydrogen and helium clouds.

• Shortest days of all planets (10hours)

• Rings made of ice particles that are very thin.

• 61 moons

Saturn

• Elaborate system of rings made of ice particles

• Rings are 250 000km wide

• Composed of mainly hydrogen and helium

• 60 moons

Uranus• Ring system made

of ice and dust• Methane gas in its

atmosphere (blue-green colour)

• Atmosphere also has hydrogen and helium

• Unusual rotation - flipped on its side

• 27 moons

Neptune

• Atmosphere is similar to Uranus.

• Very thin ring system made of ice particles.

• 13 moons

Trans-Neptunian Objects•Objects that circle the Sun beyond the orbit of Neptune

•Found in the Kuiper Belt

•Astronomers think that it is made of fragments left over from the formation of the solar system.

•Pluto is found in the Kuiper Belt and is known as a dwarf planet.

Oort Cloud

• At the farthest reaches of the Sun’s gravitational influence is a spherical cloud of icy fragments of debris called Oort.

Comets• Most start in the Kuiper Belt and

the Oort cloud.• Sometimes the comet gets too

close to Jupiter.• Jupiter’s gravitational force will

either capture the comet or nudge it closer to the Sun

• When it gets close to the Sun, the radiation from the Sun releases the gases and particles in the comet.

• The wind from the Sun make the tail of the comet.

Asteroids

• Small, non-spherical objects that are thought to be debris left over from the formation of the solar system.

• Most are in the asteroid belt found between Mars and Jupiter

Meteoroids vs Meteors vs Meteorites

• Meteoroids: Pieces of rock moving through space.

• Meteors: a meteoroid that hits Earth’s atmosphere and burns up due to atmospheric friction.

• Meteorites: a meteoroid that is large enough to pass through Earth’s atmosphere and reach the ground without being totally burned up.

The Impact of Impacts

• An asteroid about the size of a mountain struck Earth 65 million years ago.

• There were huge changes on Earth because of it.

• Extinctions: dinosaurs• Impact craters (Nunavut

and Arizona)• Probably created huge

winds and falling rock.