1. The Outer Planets Uranus, Neptune and Pluto

2. Uranus About 4 times diameter of Earth 3 billion km (1-3/4 billion miles) from Sun 84 Years to Circle Sun Rotates in 16 hours Five large satellites (500-1500 km), ten smaller ones Nine narrow rings

3. Uranus

5. Uranus Seen From Beyond

6. Uranus Shows Little Detail

7. Oberon

8. Titania

9. Umbriel

10. Ariel

11. Miranda

12. Neptune About 4 times diameter of Earth- a bit smaller than Uranus 4.5 billion km (2.8 billion miles) from Sun 165 Years to Circle Sun Rotates in 18 hours One large satellite (2700 km), seven smaller ones Four narrow rings

13. Neptune: A Twin of Uranus? No!

14. The Great Dark Spot

15. Neptune and Triton

16. Neptune’s Rings

17. Triton

18. Pluto At 2300 km, Pluto is the smallest planet Has most elliptical orbit: ranges from 4.4 to 7.4 billion km from Sun (2.8-4.5 billion miles) Actually crosses orbit of Neptune; closer to Sun than Neptune until 2009 Orbits in 248 years, 1.5 times Neptune Because of orbital tilt and resonance, cannot collide with Neptune

19. Pluto and Charon Pluto’s moon Charon is almost half as big as Pluto (1100 km) Orbits only 20,000 km away Pluto and Charon always keep same face to each other (rotation locked) Pluto rotates, and Charon revolves, in 6.4 days

20. Pluto and Charon

21. Why We Have to Go There

22. Plutinos and the Kuiper Belt The Kuiper Belt is an outer ice asteroid belt, probably the source of most comets Over 50 are now known orbiting beyond Neptune, some beyond Pluto Pluto is probably just the biggest of these objects (not really a planet?) Several dozen have periods similar to Pluto’s - 250 years - and have been dubbed “plutinos.”