1. The Planets Chapter 27

2. #1 The planets in the Solar System are divided into 2 groups. Those closest to the Sun (Mercury, Venus, Earth, Mars) are called the Inner or Terrestrial planets. These planets have rocky crusts, dense mantle layers, and very dense cores.

3. #2 Just beyond the orbit of Mars is the asteroid belt. The asteroid belt separates the Inner Planets from the outer planets. The outer planets are Jupiter, Saturn, Uranus, Neptune, Pluto. The first 4 of these are called the Jovian (Jupiter-like) planets. They are very large and made up mostly of hydrogen and helium gas. All the Jovian planets have ring systems.

4. Inner Planets

5. Outer Planets (Pluto not shown)

6. The Planet formerly known as Pluto

7. #3 Pluto is so far away that we know very little about it. Pluto isn’t always the furthest planet, but it is always the smallest planet. In a controversial move a few years ago, Pluto was demoted from planet status to “dwarf planet”. Some astronomers consider Pluto and it’s moon, Charon, to be a double planet, not a planet with a moon.

8. #4 Mercury is closest to the sun Mercury is the smallest of the terrestrial planets and orbit the sun in 88 days. Mercury has not discernable atmosphere and has great temperature variations. The surface of Mercury looks very similar to that of the Moon with all of its craters.

9. Mercury compared to Earth

10. #5 Venus is similar to Earth in diameter, mass, and gravity. Unlike other planets, Venus rotates east to west (clockwise) Venus has a thick atmosphere and extreme temperatures due to the greenhouse effect caused by the thick clouds in the atmosphere.

11. More #5 Venus can be seen from Earth and is sometimes called the Morning or Evening “star” depending upon when it is viewed. Mercury is much harder to see from Earth since it is so close to the sun.

12. #6 Mars is the 4 th planet from the Sun. Mars takes about 687 days to orbit the Sun, so a year on Mars is about twice as long as an Earth year. Since the axis of Mars is tilted similar to the tilt of the Earth’s axis, Mars experiences seasons similar to Earth.

13. More #6 Since Mars is further from the Sun than Earth, it is generally colder on Mars. Mars does have polar ice caps. There is also evidence that Mars at one time had a large amount of surface water. The largest known volcano in the Solar System is located on Mars (Olympus Mons)

14. Spirit and Opportunity on Mars surface

15. #7 Jupiter is the 5 th planet from the Sun. Jupiter takes 11.9 Earth years to orbit the Sun and rotates on it’s axis in just less than 10 hours. The most striking feature on Jupiter is the Great Red Spot, which is actually turbulence in the atmosphere.

16. Jupiter

17. #8 Saturn, the 6 th planet from the Sun, takes nearly 30 years to complete one orbit of the sun. Saturn turns on it’s axis about every 10 hours. Saturn has the lowest density of any planet. Saturn is well known for it’s beautiful ring system, which may be the remnants of one or more moons that disintegrated.

18. Saturn

19. #9 The 7 th planet from the sun is Uranus. Uranus takes 84 Earth years to orbit the sun. Uranus turns on it’s axis once every 17.2 hours. The most unusual feature about this planet is that it’ axis seems to be tipped almost completely on it’s side.

20. #10 Neptune is the 8 th planet from the sun. It has extremely high winds and extremely low temperatures.

21. #11 Pluto is way out there. It is 39.5 AU from the Sun. Since it is so far from the Sun, the temperature on Pluto is extremely cold.

22. #12 Bodies that orbit around planets are called satellites, or moons. Except for Mercury and Venus, each planet has at least one natural satellite.

23. #13 The Earth has one moon. Mars has 2 natural satellites, Phobos and Deimos. Jupiter has at least 28 moons. The largest of these are Callisto, Ganymede, Io, and Europa. They are called the Gallilean satellites in honor of who discovered them, Galileo.

24. #14 Comets have been described as dirty snowballs. They are made of particles of dust trapped in a mixture of water, carbon dioxide, methane and ammonia. Comets travel in huge elliptical orbits passing around the sun and then back out beyond Pluto. Comets become visible when they pass near the sun. The tail of the comet is actually produced by radiation from the sun.

25. Comets

26. #15 Asteroids revolve around the sun in the same direction as the planets. Most asteroids orbit the sun between the orbits of Mars and Jupiter. Asteroids may be the remnants of a planet that broke up.

27. #16 A falling star, or shooting star (it’s not really shooting and isn’t a star) is the light made by a meteoroid as it passes through the atmosphere. Sometimes a meteor shower will occur when the Earth’s orbit takes it through the tail of a comet.

28. #16 Continued If a meteor survives the trip through the atmosphere and actually hits the ground,it is called a meteorite. If the meteorite is large enough, it can make an impact crater, such as the one on the next slide.