Notes 14-3 and 14-4The Planets

Order of Planets

• Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, Pluto

• “My Very Excellent Mother Just Served Us Nine Pancakes”

Inner planets

• Mercury, Venus, Earth, Mars• Similar to each other• Small, dense, rocky• “terrestrial planets”

Mercury• Closest to sun• Smallest terrestrial planet• Weak gravity• Almost no atmosphere• Extreme temps• No moons

Venus• Venus’s density and internal structure are similar to Earth’s.

But, in other ways, Venus and Earth are very different.• Thick atmosphere, always cloudy, traps the heat, hottest

temp• “greenhouse effect”• Many Volcanoes• No Moons

Earth

• 70% liquid water at surface• Atmosphere 21% oxygen, 78% Nitrogen, 1%

other gases• 1 moon

Earth’s Layers• Earth has three main layers—a crust, a

mantle, and a core.

Mars• Mars has ice caps at both poles. Scientists

think that a large amount of liquid water flowed on Mars's surface in the distant past.

•“red Planet”•Thin atmosphere of CO2

•Many space probes have visited•Olympus Mons is largest volcano in solar system•2 small moons

Mars

The outer planets

• Jupiter, Saturn, Uranus, Neptune, Pluto??• First 4 outer planets are very large and do not

have solid surfaces; they are gas giants• Pluto is similar to the terrestrial planets

Gas Giants

• Atmosphere is mostly hydrogen and helium• Strong gravitational forces• Thick atmospheres• Cold temperatures• Many moons• Rings- thin disk of ice and rock

Jupiter

• Largest and most massive planet• 2.5x the size of all other planets combined!• Great red spot = storm that is larger than

earth

Jupiter• Jupiter is composed mainly of the elements

hydrogen and helium.

Jupiter’s Moons• The astronomer Galileo

discovered Jupiter’s four largest moons. They are named Io, Europa, Ganymede, and Callisto.

• 63+ moons

Saturn

• Saturn has the most spectacular rings of any planet. 2nd largest planet. 47+ moons.

Uranus

• Although the gas giant Uranus is about four times the diameter of Earth, it is still much smaller than Jupiter and Saturn.

• Twice as far from sun as saturn, very cold• Discovered in 1781• Tilted on its side• 27+ moons

Uranus

• Uranus’s axis of rotation is tilted at an angle of about 90 degrees from the vertical.

Neptune

• Neptune is a cold, blue planet. Its atmosphere contains visible clouds.

• Similar in size and color to Uranus• Discovered by mathematicians in 1846 who

thought it was disrupting the orbit of Uranus

- 13+ moons- Takes 165 Earth years to

Orbit sun!

Pluto

• Pluto has a solid surface and is much smaller and denser than the other outer planets.

• Considered dwarf planet in 2006 due to small size and weak gravitational pull

• Has 1 moon, half its size

Crossing orbits of Neptune and Pluto

Pluto "crossed" Neptune's orbit on January 21, 1979, and temporarily became the 8th planet from the sun. It will cross Neptune's orbit again on Feb. 11, 1999 to resume its place as the ninth planet from the Sun for the next 228 years. Despite the fact that Pluto and Neptune temporarily change places in their distance from the Sun, they will never collide. This is due to two reasons: First, Pluto's orbit is inclined to the ecliptic by 17 degrees. So even though we say the orbits cross, Pluto is actually quite a bit above Neptune. 2nd, Pluto orbits the sun twice for every 3 orbits of Neptune. The closest the 2 planets ever come to each other is 2 billion km!

Crossing Orbits of Pluto and Neptune

Size Comparisons

• http://www.kiroastro.com/writings/perspective