The Planets The Solar System is made up of 8 planets, 3 dwarf planets (Pluto, Ceres and Xena) countless asteroids and comets. The sun is by far the dominant.

The Planets

• The Solar System is made up of 8 planets, 3 dwarf planets (Pluto, Ceres and Xena) countless asteroids and comets. The sun is by far the dominant body in the solar system. It has a thousand times the mass of Jupiter, which in itself has more mass than all the planets combined. It is the Sun’s gravitational attraction therefore that controls the motion of the planets, asteroids and comets. Let’s have a quick look at these nine planets before you create a detailed chart comparing some of their more important facts. Key words and terms will be introduced throughout this presentation.

Planets and Sun to scale

Mercury

• Its symbol represents a wand with two serpents on it, carried by the God Mercury• God of Commerce and Thievery (once called Vulcan)• Smallest planet, too small to have an atmosphere • Nearest to the sun• The Composition of the planets (atmosphere and surface) can be confirmed by ‘Spectroscopy’. Different substances absorb sunlight at specific wavelengths. A Spectrum analysis will tell us what a planet is made of.

Venus

• Its symbol represents a hand mirror. Venus is the goddess of love• Due to its thick atmosphere and Greenhouse Effect, it is the hottest planet• It is the closest planet to Earth in distance• It is third to the Sun and the moon in brightness at night. It is called the ‘Evening Star’• Its rotation is extremely slow - 243 of our days. Its rotation is slower than its revolution• After the moon it was the first planet to be visited by an earth probe.• Known to have volcanic activity.

Earth

• The word means ground. Its symbol is that of a circle with the equator and Prime Meridian drawn on them

• Of course it is the only planet to have life on it. It is a dynamic planet - tectonic and erosional forces are constantly changing its surface.

• Its tilt allows the earth to have seasons - more on this later

• The plain of the Earth’s orbit is called the ‘Ecliptic’. The moon can hide behind the Sun only when it crosses this place exactly. The Moon’s orbit about the Earth is inclined 5.20 to the ecliptic and the orbits of the planets lie within 3.50 of the ecliptic.

Mars

• Its symbol represents a shield with a sphere• Named after the god of war• It is also called the ‘Red Planet’ - red colour due to iron ore content (rust)• It is most similar to Earth (in composition and tilt). Once believed to contain liquid water (Channels can be seen on it’s surface) and even LIFE!• Most people’s favourite planet - folklore and science fiction•Has frozen water in the polar regions - Ice Caps• Two moons Phobos (fear) and Deimos (panic).

Asteroids or Planetoids• The word Asteroid means star-like• They are found in a large unusual gap between Mars and Jupiter• There is a theory as to the origin of the Asteroids called: Bode’s law:

Titius Progression Planet Actual Distance from sun (AU)(0+4) / 10 = 0.4 Mercury 0.387( 3+4 ) / 10 = 0.7 Venus 0.723( 6+4) / 10 = 1.0 Earth 1.00(12+4) /10 = 1.6 Mars 1.524(24+4) /10 = 2.8(48+4) /10 = 5.2 Jupiter 5.203(96+4) /10 = 10.0 Saturn 9.539(192+4) /10 = 19.6 Uranus 19.18(384+4) /10 = 38.8 Neptune 30.6(768+4) /10 = 77.2 Pluto 39.4

• AU = Astronomical unit (distance from the earth to the sun)

1.495978893 x 10 cm = 93,000,000 miles

• Notice that Neptune and Pluto do not fit• There is no planet at the 2.8 position• The Asteroids or minor planets are found there• The belief is that the gravitational pull of Jupiter and the Sun broke up a planet that once existed at the 2.8 position• This broken planet left 1,700 smaller pieces revolving around the sun called The Asteroid Belt• The two largest asteroids are called: CERES (has been upgraded to Dwarf planet) and EROS. Ceres is 480 miles in diameter, others average 50 miles wide

• 2000 cross the earth’s orbit

• It is estimated that 5 asteroids of 1 km or greater in size will strike the earth every 1 million years

• An asteroid collision is believed to be the reason for the mass extinction of the dinosaurs

NOTE: The orbits of the planets are not perfect circles, they are egg shaped or Elliptical. The more elongated the ellipse the more ‘Eccentric’ the orbit.

A - Perihelion

B - Aphelion

AB

Remember Pluto is now not a planet, but it is interesting to see the shape of it’s orbit.

Jupiter

• Its symbol is that of a great thunderbolt in the shape of a ‘Z’ to represent Zeus (King of the Greek gods). Jupiter is the name of the King of the Roman gods.

• The first outer planet, the first of the ‘gas’ giants, Jupiter and the other large planets are called Jovian planets.

• It is the largest planet

• Known for it ‘great red spot’, believed to be a continuous storm on the planet

• Jupiter rotates in just under ten hours!

•It has rings

• Four of its 16 moons were discovered by Galileo Galilei in 1610 (Io, Europa, Ganymede, Callisto)

• Io has active volcanoes and even an atmoshere.

• Europa has water as solid, some even think as a liquid.

Saturn

• Named after the god of time. Its symbol is a cane shaped like a sickle

• Most recognizable and beautiful due to the magnificent rings that surround the planet, believed to be a broken up moon. The rings are in 3 major parts separated by a division called Cassini’s division.

• One of Saturn’s moons is actually bigger than the planet Mercury.

• Its density is lighter than water. Saturn can float!

• It has 18 moons or satellites. Titan has a substantial atmosphere.

Uranus

• Named after the god of the sky. Its symbol represents the sky

• Discovered in 1781 by telescope, barely bright enough to see with the unaided eye.

• It also has rings as well

• Due to its tilt (980) Uranus’ nights could last up to 21 years.

• It has a bluish green colour due to its methane atmosphere.

Since we have mentioned the tilt of a number of planets here is a diagram that shows all of the tilts.

Neptune

• Named after the god of the sea, so naturally its symbol is a trident

• The last of the gas giants

• It was discovered in 1846. It cannot be seen without a telescope.

• Neptune is blue in colour. It’s methane atmosphere is denser than that of Uranus.

• Because of Pluto’s very elliptical orbit (It actually crosses Neptune’s orbit) Neptune was further away from the sun for a number of years.

Pluto – A Dwarf Planet

• Named after one of the people that discovered it. Pluto represents the god of the underworld.

• Discovered in 1930

• Downgraded to Dwarf planet because it is too small in 2006

• Due to its tremendous distance from the sun very little is known about Pluto

• Theory goes that it was a rogue planet captured by our Sun’s gravitational pull

• Pluto has a moon called Charon, some say that they are double planets.

• Only planet not visited by an earth probe.

The Kuiper Belt

• Theorized to exist in 1951. The first object to be found there was in 1992.

• Today there are more than 240 objects found in the belt

• Some comets (short period) are found here. Just outside the Kuiper Belt is another zone that is believed to house most of the long period comets called the ‘Oort cloud’. These comets have very eccentric orbits thus passing by the earth once every 75 to 100 years (Eg. Halley’s Comet)

• Xena – the third Dwarf planet is found here.

The End!