1. The Planets 7.3

2. What are some of the objects that make up our solar system? Planets Moons The Sun Comets Asteroids Stars

3. What is the center of the solar system? The Sun

4. The Solar System What is the Solar System? The solar system is the Sun and all the objects that orbit around the Sun. What is a planet? A planet is a large object orbiting a star.

5. Our Solar System Our solar system is made up of 8 planets orbiting the Sun.

6. What is a moon? A moon is a natural object that orbits a planet. In our solar system all but 2 planets have one or more moons.

7. Planets The planets in our solar system travel in an elliptical orbits around the Sun.

8. Planets in our solar system in order (nearest to the Sun to farthest away) Mercury Venus Earth Mars Jupiter Saturn Uranus Neptune

9. Other objects in space Comets Asteroids Meteors

10. Comets A comet is a mixture of frozen gases, ice, dust, and rock that moves in an elliptical orbit around the Sun.

11. Asteroids An asteroid is a rock that revolves around the Sun. Most are located between Mars and Jupiter in the asteroid belt. Sizes of asteroids vary. They can be less than 1 mile wide or as big as 500 miles wide!

12. Meteoroids Meteoroids are small objects in space. Objects that cross paths with Earth and enters Earth’s atmosphere is called a meteor. Most of these objects, meteors, burn up as they travel through Earth’s atmosphere. The meteors that do make through Earth’s atmosphere and land on the ground are called meteorite.

13. Inner Planets The inner planets are closer to the Sun than the asteroid belt. They are Mercury, Venus, Earth, and Mars. Common characteristics of inner planets: – Surfaces made of rock – Their orbits are spaced close together. – Few or no moons – No rings

14. Which planet is closest to the Sun? Mercury How many moons do each of the inner planets have? Mercury- 0 Venus- 0 Earth- 1 Mars- 2

15. Outer Planets 4 outer planets located beyond the asteroid belt. Jupiter, Saturn, Uranus, and Neptune Common characteristics: – Made mostly of gas and sometimes called gas planets – Metallic core and thick atmosphere – Orbits are spaced far apart. – All have rings and many moons. – Days are very short and they spin rapidly on their axes.

16. How do the outer planets differ in size from the inner planets? The outer planets are much larger than the inner planets.

17. Why are the outer planets called gas planets? The outer planets are made of various gases, not rock.

18. What is a moon? A moon is a natural object that orbits a planet. Different planets have different numbers and sizes of moons. Inner planets have fewer moons than the outer planets.

19. Satellite A satellite is an object in space that circles around another object. Moons are natural satellites. People put artificial satellites in space. Some of these are weather and communications satellites and space probes.

20. Sizes of Moons The sizes vary. The largest moon in the solar system is Jupiter’s Ganymede. It is larger than Pluto and Mercury. Earth’s moon is also larger than Pluto.

21. Craters When small objects in space collide with large objects craters form on the larger surface. A crater is a bowl-shaped hole. Earth’s moon craters can be seen from Earth.

22. Exploration of our Solar System All the planets in our solar system have been explored using space probes. A space probe is a vehicle carrying instruments that is sent to explore objects in space.

23. Moon Exploration In 1969 the United States sent the first astronauts to the Moon. The Moon is the only place in space that astronauts have explored.

24. Exploring Mars Two rovers, Spirit and Opportunity, were placed on Mars in 2004. Rovers are small robot cars. These rovers were equipped with cameras and took pictures of soil, pebbles, and rocks. Instruments on the rover found evidence that liquid water may have once existed on Mars.

25. Space probe is on it’s way to Pluto! A space probe, New Horizons, was launched in January 2006 heading for Pluto. The probe is planned to land on Pluto in 2015.

26. Review Time!!! If scientists found a natural object moving around a planet, what would they call it? Since this natural object is moving around a planet, scientists will most likely call it a moon.

27. Other than planets, what other objects are in a solar system? Stars, moons, asteroids, meteoroids, and comets.

28. If you went on Venus, in what direction would you see the Sun rise and set? Venus rotates in the opposite direction from earth. On Venus, if you could see the Sun through its thick clouds, the Sun would appear to rise in the west and set in the east.

29. How are the inner planets alike? How are they different? The planets all have surfaces made of rock. They vary in size.

30. If scientists discover a new planet that appears to be the same color as Uranus, what can you infer about its atmosphere? The methane in Uranus’ atmosphere causes the planet to have a blue appearance. If a newly discovered planet has a blue appearance, you could infer that this planet also contains methane in its atmosphere.

31. Name one way Saturn differs from other planets. Saturn’s rings are more noticeable than the other planets’. Saturn is smaller than Jupiter, but larger than Uranus and Neptune.

32. How are a moon and an artificial satellite different? A moon is a natural object that orbits a planet. An artificial satellite also orbits a planet, but it was put in to space by humans.

33. What happens when objects in space collide with Earth? Smaller objects burn up in Earth’s atmosphere. Larger objects reach the ground and form craters.

34. What might be inferred from the discovery that liquid water may once have existed on Mars? As far as we know, liquid water must be present for life to exist. The discovery of liquid water on Mars means that life may have existed on Mars at one time.