Chapter 21: A Family of Planets

Section 1: Our Solar System

Solar system includes the sun, planets and many smaller objects.

Measuring interplanetary distances1. Astronomical unit- distance between

the sun and earth

2. Light minute- time it takes light from the sun to reach earth

1 AU= 8.3 light minutes

Discovery of the solar system1. Earth, Mercury, Venus, Mars,

Jupiter, Saturn, sun, earth’s moon2. Moons of Jupiter and Saturn3. Uranus and its moons, Saturn and

its moons, Neptune and its moons4. Pluto

Inner Planets: My Very Eager Mother

• Dense and rocky

Outer planets: Just Served Us Nachos

- Large and are Composed mostlyof gases

Order of planets from closest to farthest from the sun

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

My Very Eager Mother Just Served Us Nachos

Section 2: Inner planets

- Also called terrestrial planets because they are very dense and rocky.

1. Mercury: Closest to the Sun

Mercury statistics:Distance from the sun: 3.2 light

minutesPeriod of rotation: 58 days, 19 hPeriod of revolution: 88 daysGravity: 38% of Earth’s

2. Venus: Earth’s twin?Venus Earth

Sun rises in the west, sets in the East

Sun rises in the East, sets in the west

Retrograde rotation: clockwise direction

Prograde rotation: counterclockwise direction

12,104 km 12,756 km

91 % of earth’s gravity 100% of earth’s

Denser atmosphere Less dense atmosphere

Venus: Hottest Planet

The atmosphere is mostly carbon dioxide which traps thermal energy from the sun causing greenhouse effect.

The Greenhouse effect causes the temperature to

be very high.

3. Earth: An Oasis in Space

Statistics:Distance from the sun: 8.3 light

minutesRotation: 23 h, 56 minRevolution: 365 days, 6 hGravity: 100 % of earth’s

4. Mars:

- Shows evidence of once having water stored on polar ice caps

- Has a rich volcanic history: Tharsis and Olympus Mons (largest mountain in the solar system)

What characteristics of Mars may explain why Mars has only two large volcanic systems?

Mars’ crust is not active, so the Martian crust does not move. As a result, volcanoes tend to form continually in only a few areas on Mars.

Section 3: The Outer Planets

Jupiter- Largest planet- Made of hydrogen and heliumGreat Red Spot- a storm system

more than 400 years old and 3 times the diameter of earth

Gravity: 236% of Earth’s

Saturn: second largest planet

Rings of Saturn are made of icy particles ranging in size from a few centimeters to several meters wide.

Uranus: A small giant-discovered by William Herschel-atmosphere is made of hydrogen

and methane- Blue green in color because H and

methane absorb the red part of the sunlight

strongly

Uranus: A tilted Planet- Uranus is tipped over on its side- Axis of rotation is tilted by 90

degrees and lies in the plane of its orbit

Neptune: The Blue world

Neptune’s interior releases energy to its outer layers, which creates belts of clouds in Neptune’s atmosphere.

Pluto: A dwarf planet

In 2006, astronomers created a new definition of planet. Pluto does not fit all of the conditions for it to be considered a planet, Pluto has been reclassified as a dwarf planet.

Definition of planet:

1. A planet orbits the sun2. A planet is round because of its

own gravity3. A planet has cleared the

neighborhood around its orbital path

***Pluto has not cleared the area around its path of debris.