Class 24: Uranus, Neptune, Pluto Solar System Distances 39 AU 30 AU *Planets not to scale Distances not to scale 19 AU Uranus: A Global Perspective Differences Earth Uranus • Size (radius) 6738 km 4x Earth • Mass 6x1024 kg 145 Earth • Density 5.5 g/cm3 1.3 g/cm3 • Atmosphere 78%N2 21%O2 84%H 14%He 2%CH4 (methane) • Surface temperature 20°C -200°C • Rotation 1 day -17.9 hours 1 Exploring Uranus Herschel Uranus moons Voyager 2 Hubble Space Telescope Uranus’s Interior (1) (2) core Axis of Rotation 23.5° 98 ° Earth Uranus 2 Atmosphere & Magnetic Field ultraviolet magnetic axis visible rotation axis 60° The Rings of Uranus dust bands The Moons of Uranus Oberon (2nd largest) Titania (largest) r ≈ 789 km Umbriel Miranda Puck Ariel 3 Neptune: A Global Perspective Differences Earth Neptune • Size (radius) 6378 km 3.9x Earth • Mass 6x1024 kg 171 Earth • Density 5.5 g/cm3 1.6 g/cm3 • Atmosphere 78%N2 21%O2 84%H 14%He 2%CH4 (methane) • Surface temperature 20°C -210°C • Rotation 1 day 16 hours Exploring Neptune Adams Le Verrier Galle Voyager 2 HST Neptune’s Interior (1) H, He, CH4 (2) H2O, CH4, NH3 core 4 Neptune’s Atmosphere & Clouds Neptune clouds cloud bands Scooter The Great Dark Spot Voyager 2 Voyager 2 Voyager 2 GDS changes Neptune’s Rings & Moons twisted ring? faint rings Nereid Triton 5 A Parting Look Pluto: A Global Perspective Similarities Earth Pluto • Moon 1 - Moon 1 - Charon Differences • Size (radius) 6378 km 0.2x Earth • Mass 6x1024 kg 0.002x Earth • Density 5.5 g/cm3 0.4x Earth • Atmosphere 78% N2 21% O2 probably N2, thin • Surface temperature 20°C -230°C • Rotation 1 day 6.4 days * Pluto’s orbit is VERY eccentric (sometimes inside Neptune)! Exploring Pluto Tombaugh, Lowell Observatory Photo 1 Photo 2 planetary symbol Charon 6 Pluto’s Interior (1) core Pluto: Is it a planet? Rose Center for Earth & Space, New York City Pluto - Charon System 112° 7 Pluto and Charon from Hubble Bright/dark regions: differences in methane/nitrogen frost cover New Horizons Mission • Lanch window: January 2006 • Interplanetary cruise: 2007 - 2015 • Pluto-Charon encounter: 2015 Uranus • Satellites 27 • Size (radius) 25,900 km • Density 1.3 g/cm3 • Orbit 84.01 years • Rotation -17.9 hours • Atmosphere 83% H , 15% He, 2% CH4 (methane) • Surface pressure 1.2 atm • Surface temperature -200°C (at cloud surface) 8 Neptune • Satellites 13 • Size (radius) 24,746 km • Density 1.6 g/cm3 • Orbit 165 years • Rotation 17 hr, 15 min. • Atmosphere 95% CO2, 3% N2 • Surface pressure 0.01 atm • Surface temperature -210°C Pluto • Satellites 11 • Size (radius) 1137 km • Density 2.05 g/cm3 • Orbit 248 years • Rotation -6.4 days • Atmosphere N2? • Surface pressure 1.2 atm • Surface temperature -193°C 9.