GEOL 3045: Planetary Geology Lysa Chizmadia Uranus Lysa Chizmadia Uranus

Introduction  3rd largest planet –Seventh from Sun (or eighth)  1st discovered in modern times –1781 by William Herschel  Eccentricity = – AU  Axial Tilt = 97.9º –Earth = 23.5º  Orbital period = 84.1 years –Each pole 42 years continuous Sun, then dark  Rotational period = 17.9 hours  Mass = 8.69 x kg –~14.5 Earths  Average  = 1.29 g/cm 3 –   = 5.52 g/cm 3 (2nd lowest  in solar system)  At least 27 moons  3rd largest planet –Seventh from Sun (or eighth)  1st discovered in modern times –1781 by William Herschel  Eccentricity = – AU  Axial Tilt = 97.9º –Earth = 23.5º  Orbital period = 84.1 years –Each pole 42 years continuous Sun, then dark  Rotational period = 17.9 hours  Mass = 8.69 x kg –~14.5 Earths  Average  = 1.29 g/cm 3 –   = 5.52 g/cm 3 (2nd lowest  in solar system)  At least 27 moons Image from: Image from:

Internal Structure  Atmosphere: –Pressure: 1.2 bars  Earth: ~ 1 bar –Outer 20% of radius  ~0.5 Earth masses –~83% H, ~15% He & 2% CH 4  Blue color due to absorption of red light by methane  Icy mantle –~13.4 x Earth masses –Hot dense fluid –Composition: H 2 O, NH 3, etc. –High electrical conductivity  Rocky Core: –~0.55 x Earth masses –  ~ 9 g/cm 3 –P ~ 8 Mbars –T ~ 5000 K  Atmosphere: –Pressure: 1.2 bars  Earth: ~ 1 bar –Outer 20% of radius  ~0.5 Earth masses –~83% H, ~15% He & 2% CH 4  Blue color due to absorption of red light by methane  Icy mantle –~13.4 x Earth masses –Hot dense fluid –Composition: H 2 O, NH 3, etc. –High electrical conductivity  Rocky Core: –~0.55 x Earth masses –  ~ 9 g/cm 3 –P ~ 8 Mbars –T ~ 5000 K Image from:

Atmosphere  Structure: –Troposphere  Highly complex cloud structure –H 2 O clouds –NH 4 HS clouds –NH 3 or H 2 S clouds –CH 4  Responsible for Far IR emissions –T ~ 59 K –Stratosphere  Contains H-Cs formed from UV radiation of CH 4  May be responsible for bland appearance –Thermosphere/Corona  H 2 and H  Extends 2 Uranus radii (~8 Earth radii)  Structure: –Troposphere  Highly complex cloud structure –H 2 O clouds –NH 4 HS clouds –NH 3 or H 2 S clouds –CH 4  Responsible for Far IR emissions –T ~ 59 K –Stratosphere  Contains H-Cs formed from UV radiation of CH 4  May be responsible for bland appearance –Thermosphere/Corona  H 2 and H  Extends 2 Uranus radii (~8 Earth radii) Images from: False color showing banding

Climate  At equator, winds retrograde – m/s  Wind speeds  to 60  lat – m/s  Towards poles, winds prograde  At poles, winds fall to 0 m/s  Dark spots common on Neptune never observed on Uranus until 2006  At equator, winds retrograde – m/s  Wind speeds  to 60  lat – m/s  Towards poles, winds prograde  At poles, winds fall to 0 m/s  Dark spots common on Neptune never observed on Uranus until 2006 Images from: White Storm Dark Spot

Rings  Dark ring system  2nd discovered  At least 13 distinct rings  Opacity & gaps indicate recent formation  Probably from shattered satellite  Dark ring system  2nd discovered  At least 13 distinct rings  Opacity & gaps indicate recent formation  Probably from shattered satellite Images from: False color to show structure Inner Rings Images from: Shepherd SatellitesFine Structure

Magnetic Field  ~50 x Earth’s magnetic field  Tilted 59  from rotation axis  Not centered with planet –~1/3 towards south pole  Therefore, highly asymmetric –Strength in S ~0.1 G –Strength in N ~1.1 G  ~ Neptune  May be generated in CH 4 - H 2 O ocean instead of in core  ~50 x Earth’s magnetic field  Tilted 59  from rotation axis  Not centered with planet –~1/3 towards south pole  Therefore, highly asymmetric –Strength in S ~0.1 G –Strength in N ~1.1 G  ~ Neptune  May be generated in CH 4 - H 2 O ocean instead of in core Image from:

Heat Output  Coldest of giant planets –49 K (~ same as Pluto)  Neptune radiates 2.6 x more heat than receives from Sun –Uranus radiates almost none  Heat flux < Earth  Hypotheses: –When knocked over, lost primordial heat –Barrier in atmosphere prevents heat from reaching space  Coldest of giant planets –49 K (~ same as Pluto)  Neptune radiates 2.6 x more heat than receives from Sun –Uranus radiates almost none  Heat flux < Earth  Hypotheses: –When knocked over, lost primordial heat –Barrier in atmosphere prevents heat from reaching space Image from:

Summary  1st discovered in modern times  2nd least dense planet  Internal structure –Atmosphere –Icy mantle (hot, dense liquid) –Rocky core  Rotates on side –Probably due to massive collision  Complex atmospheric structure –Troposphere –Stratosphere –Thermosphere/Corona  Asymmetrical magnetic field  Coldest of giant planets  1st discovered in modern times  2nd least dense planet  Internal structure –Atmosphere –Icy mantle (hot, dense liquid) –Rocky core  Rotates on side –Probably due to massive collision  Complex atmospheric structure –Troposphere –Stratosphere –Thermosphere/Corona  Asymmetrical magnetic field  Coldest of giant planets Image from: