1. The Solar System

2. What is a planet? Old Definition
a large, solid body that shines by reflecting sunlight and revolves in a stable orbit around the Sun

3. What is a planet? New Definition
3 major criteria are required to classify an object as a planet:
a large solid body that shines by reflecting sunlight and revolves in a stable orbit around the sun
large enough that its own gravity pulls it into a round shape
large enough to clear the path of its orbit

4. Classifying Planets
Inner Planets are between the Sun and the Asteroid Belt. They are inside the belt.
Outer Planets are farther from the Sun. They are outside the Asteroid Belt.
The Asteroid Belt is between Mars and Jupiter.

5. Inner Planets
Which planets are the inner planets?

6. Inner Planets Which ones are the inner planets?
Mercury, Venus, Earth, Mars
Inner planets are also called terrestrial planets. Why?

7. Inner Planets Which ones are the inner planets?
Mercury, Venus, Earth, Mars
Inner planets are also called terrestrial planets. Why?
made mainly of rock

8. Mercury
Mercury has almost no gravity so it cannot hold on to an atmosphere. Without an atmosphere and being close to the sun causes temperatures to be very high during the day and very low at night.

9. Venus
Called Earth’s twin because they have similar gravity, mass, and are close to one another.
Because of its thick atmosphere, a lot of heat is trapped, making the planet very hot.

10. Earth

11. Mars
Mars is red because there is a substance called iron oxide in the soil. The largest volcano in the solar system is on Mars. Mars was named after the god of war. The names of its two moons, Phobos and Deimos, mean panic and fear.
Currently there are several satellites in orbit around Mars
Crewed missions to Mars are planned.

12. The Asteroid Belt separates the Inner and the Outer Planets.

13. Asteroid belt between Mars and Jupiter
consists of thousands of rock fragments in orbit around the Sun
largest asteroids have been reclassified as dwarf planets

14. Many objects in the Asteroid Belt have names.

15. Asteroid Belt

16. The Outer Planets are outside of the Asteroid Belt.↓

17. Outer planets Which planets are included in the outer planets?
Jupiter, Saturn, Uranus, Neptune
made mostly of frozen hydrogen and helium
atmospheres can be made of thick layers of gas

18. Outer planets also known as Gas Giants or Jovian Planets
known to have a lot of moons due to large mass and gravitational pull

19. Jupiter largest planet in the solar system
Gives out more heat into space than it receives from the sun
has spots

20. Saturn takes 30 years to complete one orbit around the sun
lowest density of any planet; its density is lower than that of water!
Gives out more heat than it receives

21. Uranus – rotates on its side
has a blue color due to a substance called methane gas in its atmosphere
so far from the sun that its temperature is -348 degrees Fahreneheit
has 42 years of dark winter followed by 42 years of constant summer

22. Neptune discovered mathematically
has winds of 2000 kilometers per hour

23. Voyager 1 launched in 1977 finished a survey of outer planets in 1989
uses radioactive power packs
travels at 17 km/s
its radio message takes 16 hours to reach Earth

24. Pluto Dwarf Planet
In 2006 Pluto was reclassified as a Dwarf Planet. To be a Dwarf Planet, an object has to be round and orbit the sun, not be a moon, and not able to clear the path of its orbit.
Pluto is very different from the outer planets. It is much smaller and it is more like a terrestrial planet than a gas giant.
Pluto has three moons, Charon, Nix and Hydra.

25. Pluto is not a planet anymore!
Pluto’s orbit is not considered stable.
It crosses Neptune’s orbit.

26. Kuiper Belt ↓

27. Pluto is not a planet anymore. It is part of the Kuiper Belt.
The Kuiper Belt is a region of debris 4.5 to 7.5 billion km (2.8 billion to 4.6 billion miles) from the sun.
The Kuiper Belt is 30 to 50 Astronomical Units (AU) from the sun. One AU is the distance from the Sun to Earth.
Pluto is a Kuiper Belt Object or KBO.
So far 1300 objects in this belt have been identified. Pluto and three others are considered dwarf planets. There may be as many as 70,000 objects in the belt!