A Closer Look at the Planets of our Solar System

• Describe origin of planets.• Name the planets.• Know some facts about each planet.

KEY WORDSGas giants Terrestrial

M V E Mo J S U N P

Planets are smaller than stars and do not emit light.

Infrared Astronomical Satellite (IRAS) – 1983• found large cloud of particles around star Vega.• first evidence of solid matter around a star (other than the Sun)

• Astronomers think clouds of matter are first stage in formation of planets.

• Hubble Space Telescope has obtained images of planetary systems being formed.

Outer region• Gases cooled and condensed• Attracted by gravity, clustered together.• Formed the Gas giants planets.• Jupiter, Saturn, Uranus and Neptune are

mainly composed of these materials.

Formation of the Solar System• Nebula made mostly of hydrogen and helium.• Iron, rock and ice made up about 1%.• Matter from explosions of nearby supernova.

Nebula

Attracted by gravity, clustered together.

• hydrogen and helium.• Iron, rock and ice

Inner region• Gases in the inner region too hot to condense.• Chunks of iron and rock collide and stick

together.• Forming Terrestrial planets.• Mercury, Venus, Earth and Mars are composed

of rock and iron, with little helium and hydrogen.

The Inner Planets

Closest to the Sun• Receives sunlight 10x brighter than Earth• Day temperatures over 400°C No atmosphere - so night temp fall to -180°C• Many craters suggests collisions.• Seen few times a year, before sunrise/after sunset• Day – 59 Earth days • Year – 88 Earth days• It rotates so slowly that it’s year is

not even 2 days long.

Mercury

3rd brightest object in the sky (Sun/Moon brighter).

• Thick CO2 atmosphere reflects sunlight.

• CO2 traps Sun’s heat (greenhouse).• Hot surface seems to glow in the dark - + 465°C.• Many volcanoes eject tonnes of sulphur. Clouds of sulphuric acid makes – acid rain.• Day – 243 Earth days • Year – 225 Earth days• It’s year is shorter than it’s day.

Venus

• Ideally suited for life as we know it. • Atmosphere is mostly nitrogen, oxygen, water.• Ozone filters some damaging radiation from

Sun. Atmosphere stabilizes temperatures.• Ranges from -85°C (poles), to +65°C (equator). Water covers about 70% of Earth’s surface.• Generally stable surface – some volcanoes, earth

quakes.• Day – 1 Earth days • Year – 365 1/4 Earth days

Earth

Bright - iron oxide dirt makes it look reddish.• Very dry and barren (now).• May have had glaciers and water.• Most studied planet – no signs of life… yet. • Olympus Mons - biggest volcano/mountain in our Solar System Of all planets, Mars is most like Earth.• Surface temp ranges from -120°C to +30°C • Day – 1 Earth days • Year – 687 Earth days

Mars

The Outer Planets Asteroid Belt separates the inner and outer planets• These planets appear to lack solid surfaces, but theses

gases may become liquid or solid deeper inside the atmosphere.

• Cores may contain metals (as do the inner planets).

Largest of the planets (11x bigger than Earth).• Greater mass than all other planets combined.• Coloured bands - streams of gas clouds moving at different speeds. Great Red Spot is a continuing hurricane storm.• Has 63 moons (2006)• Temp around -160°C• Has ring of rocks cannot be seen from Earth.• Day – 10 Earth hours • Year – 11.9 Earth years

Jupiter

• 2nd largest of the planets.• Least dense – very light for size – may not even

have a solid core. Very windy – rotates very fast.• Temp around -180°C Rings stretch from Earth to Moon.• Has over 1000 rings – could be crushed moon.• Has at least 60 moons (2006)• Day – 11 Earth hours • Year – 29.5 Earth years

Saturn

Rotates on its side.• Atmosphere much like other gas giants.• Extremely cold -210°C Has several narrow, dark rings.• Has 27 moons• Day – 17 Earth hours • Year – 84 Earth years

Uranus

• Only discovered because its gravity “tugs” on Uranus’s orbit causing changes.

• Looked for another planet – found Neptune. Blue and white – methane in atmosphere. The Great Dark Spot is a gigantic storm.• Extremely cold -220°C• Has some thin rings.• Has 13 moons• Day – 16 Earth hours • Year – 165 Earth years

Neptune

Reclassed as a dwarf planet in 2006.(International Astronomical Union)

• Orbit is squished – it crosses Neptune and is sometimes closer to Sun (1979 – 1999)

No atmosphere – not a Gas giant.• Extremely cold -220°C• Has 3 moons!• Day – 6 Earth days • Year – 248 Earth years• Scientists have found other

dwarf planets – some bigger.

Pluto