GEOL 3045: Planetary GeologyGEOL 3045: Planetary Geology

Lysa ChizmadiaUranus

Lysa ChizmadiaUranus

IntroductionIntroduction 3rd largest planet

– Seventh from Sun (or eighth) 1st discovered in modern times

– 1781 by William Herschel Eccentricity = 0.046

– 18 - 20 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 1025 kg

– ~14.5 Earths Average = 1.29 g/cm3

= 5.52 g/cm3 (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 = 0.046– 18 - 20 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 1025 kg

– ~14.5 Earths Average = 1.29 g/cm3

= 5.52 g/cm3 (2nd lowest in solar system) At least 27 moons

Image from: http://en.wikipedia.org/wiki/Uranus

Image from: http://www.solarviews.com/eng/uranus.htm

Internal StructureInternal Structure Atmosphere:

– Pressure: 1.2 bars Earth: ~ 1 bar

– Outer 20% of radius ~0.5 Earth masses

– ~83% H, ~15% He & 2% CH4 Blue color due to absorption of red light by methane

Icy mantle– ~13.4 x Earth masses– Hot dense fluid– Composition: H2O, NH3, etc.– High electrical conductivity

Rocky Core:– ~0.55 x Earth masses ~ 9 g/cm3 – 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% CH4

Blue color due to absorption of red light by methane Icy mantle

– ~13.4 x Earth masses– Hot dense fluid– Composition: H2O, NH3, etc.– High electrical conductivity

Rocky Core:– ~0.55 x Earth masses ~ 9 g/cm3 – P ~ 8 Mbars– T ~ 5000 K

Image from: http://www.solarviews.com/eng/uranus.htm

AtmosphereAtmosphere Structure:

– Troposphere Highly complex cloud structure

– H2O clouds– NH4HS clouds– NH3 or H2S clouds– CH4

Responsible for Far IR emissions– T ~ 59 K

– Stratosphere Contains H-Cs formed from UV

radiation of CH4

May be responsible for bland appearance

– Thermosphere/Corona H2 and H Extends 2 Uranus radii (~8 Earth

radii)

Structure:– Troposphere

Highly complex cloud structure– H2O clouds– NH4HS clouds– NH3 or H2S clouds– CH4

Responsible for Far IR emissions– T ~ 59 K

– Stratosphere Contains H-Cs formed from UV

radiation of CH4

May be responsible for bland appearance

– Thermosphere/Corona H2 and H Extends 2 Uranus radii (~8 Earth

radii) Images from: http://en.wikipedia.org/wiki/Uranus

False color showing banding

ClimateClimate At equator, winds retrograde

– 50-100 m/s Wind speeds to 60 lat

– 150-200 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– 50-100 m/s

Wind speeds to 60 lat– 150-200 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: http://en.wikipedia.org/wiki/Uranus

White Storm

Dark Spot

RingsRings 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: http://en.wikipedia.org/wiki/Uranus

False color to show structure

Inner Rings

Images from: http://www.solarviews.com/eng/uranus.htm

Shepherd SatellitesFine Structure

Magnetic FieldMagnetic 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 CH4-

H2O 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 CH4-

H2O ocean instead of in coreImage from: http://en.wikipedia.org/wiki/Uranus

Heat OutputHeat 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 spaceImage from: http://en.wikipedia.org/wiki/Uranus

SummarySummary 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: http://en.wikipedia.org/wiki/Uranus