1. Review: What did Kepler study? What is an ellipse? Why is Mars called the red planet? Why is Venus called Earth’s twin? What do the four terrestrial planets have in common? _____ are loops of gas on the sun that link different parts of sunspot regions together

2. Chapter 20 Section 4: Outer planets Key concepts: What characteristics do the gas giants have in common? What characteristics distinguish each of the outer planets? Key terms: gas giant, ring

3. Gas giants and pluto Four outer planets – Jupiter, Saturn, Uranus, Neptune – much larger and more massive than Earth, and they do not have solid surfaces (often called gas giants) Composed mostly of hydrogen and helium. Massive, so have a high gravitational force Despite the name, much of the hydrogen and helium are in liquid form because of the enormous pressure

4. Gas giants continued Outer layers are extremely cold Each have many moons Each are surrounded by rings A ring is a thin disk of small particles like ice and rock

5. Jupiter Jupiter is the largest and most massive planet (about 2.5 times ALL other planets COMBINED) Atmosphere – thick of H and He; giant red spot (storm larger than Earth), no land Structure – probably has a core of dense rock; thick mantle of H and He, extreme pressure Moons – Io, Europa, Ganymede, Callisto (four discovered by Galileo). Has many others.

6. Saturn Second largest planet Thick atmosphere of H and He Only planet whose average density is less than that of water Rings – “most spectacular rings of any planet” Moons – largest moon, Titan; four others

7. Uranus Four times the diameter of Earth Looks blue green because of methane Surrounded by rings Discovery – 1781 – Herschel Exploring – tiled at 90 degrees from the vertical (rotating top to bottom rather than side to side) Moons – 5 largest have icy, cratered surfaces – Has at least 27 moons

8. Neptune Even farther from the sun than Uranus, but similar to it Cold, blue planet. Atmosphere has visible clouds Discovery of Neptune – because of a mathematical prediction that an unseen gravitational force was pulling on Uranus

9. Exploring Neptune Great Dark Spot – probably a storm Moons – at least 13, largest is Triton

10. Pluto Solid surface and much smaller and denser than the other planets Smaller than Earth’s moon Revolves around the sun every 248 years Now called a dwarf planet because of its slow revolution