1. Unit 13 Planets

2. What is a planet?

3. Old Definition A planet is a body that orbits a star, shines by reflecting the star's light and is larger than an asteroid.

4. New Definition The International Astronomical Union (IAU), defines a planet as an object that orbits a star, is large enough to have settled into a round shape and, crucially, "has cleared the neighborhood around its orbit."

5. How did they form? Remember the nebular hypothesis? Our solar system started 4.6 billion years ago as a cloud of dust rotating in space. 10% of the cloud made up the platelike disk around the sun. As the cloud spun large pieces of debris would collide to form planetesimals.

6. What are the 2 groups? Rocky

7. Gas Giants

8. Terrestrial (Inner-Rocky) Rocky crust Dense mantle layers Very dense cores

9. Jovian (Outer-Gas Giants) Much larger No solid surfaces Mainly hydrogen and helium They all have rings

10. Mercury Closest to the Sun No atmosphere Surface temp between -280 o F and +800 o F Hot enough to melt lead and zinc Almost cold enough for liquid oxygen to form Day is nearly 59 days long Year is 88 days

11. Mercury

12. Venus Hotter than Mercury, even though almost twice as far from the Sun Its day (243 days) is longer than its year (224 days Atmosphere is about 96% CO 2 Air pressure 90 times that of Earth Sulfuric acid clouds

13. Venus

14. Earth Only planet with chocolate Only planet with liquid water Only known life, so far, in the solar system

15. Mars A bit more than half the diameter of Earth Surface area a bit less than land mass of Earth Day is about 24.5 hours, Year about 22.5 months Atmosphere less than 1% of Earth’s 2 moons Phobos, average diameter, 13.8 miles Deimos, average diameter, 7.8 miles

16. Mars

17. Phobos

18. Deimos

19. Jupiter King of the planets Weighs more than all the other planets combined Over 1300 Earths could fit inside Magnetic field is 20,000 times Earth’s Nearly 90% hydrogen At least 63 moons

20. Jupiter

21. Moons of Jupiter Biggest moon, Ganymede, larger than Mercury Europa, bigger than Pluto, nearly as large as the Moon Io, most volcanically active body in the solar system. Larger than the Moon Callisto, almost as large as Mercury These 4 moons were discovered by Galileo

22. Ganymede

23. Io

24. Callisto

25. Europa