GEOL 3045: Planetary Geology Lysa Chizmadia Neptune Lysa Chizmadia Neptune

Introduction  4th largest –Diameter: 4.95 x 10 4 km –~4 x Earth  8th from Sun (or 9th) –30 AU (Uranus 19 AU) –Discovered 1846  Eccentricity:  Axial Tilt:   Orbital Period: yrs  Rotational Period: hrs  Mass: x kg –~17.1 x Earth  Average  = 1.64 g/cm 3  At least 13 moons  4th largest –Diameter: 4.95 x 10 4 km –~4 x Earth  8th from Sun (or 9th) –30 AU (Uranus 19 AU) –Discovered 1846  Eccentricity:  Axial Tilt:   Orbital Period: yrs  Rotational Period: hrs  Mass: x kg –~17.1 x Earth  Average  = 1.64 g/cm 3  At least 13 moons Images from: Images from:

Internal Structure  Atmosphere: –1-2 Earth masses –Grades into mantle  Higher [H 2 O] [CH 4 ] [NH 3 ] with increasing depth  Mantle: –10-15 Earth masses –Mostly H 2 O, CH 4, NH 3 –High P & T (liquid) –High electrical conductivity –At 7000 km, CH 4 may decompose into diamond  Core: –~1.2 Earth mass –Rock & ice –P: ~7 Mbars –T: ~5400 K  Atmosphere: –1-2 Earth masses –Grades into mantle  Higher [H 2 O] [CH 4 ] [NH 3 ] with increasing depth  Mantle: –10-15 Earth masses –Mostly H 2 O, CH 4, NH 3 –High P & T (liquid) –High electrical conductivity –At 7000 km, CH 4 may decompose into diamond  Core: –~1.2 Earth mass –Rock & ice –P: ~7 Mbars –T: ~5400 K Images from: Images from:

Atmosphere  Pressure: 1-3 bars  Composition: –85% H, 13% He, 2% CH 4  At high altitudes –80% H, 19% He –Blue color due to absorption of red light by methane  Atmosphere divided ~ Uranus –Thermosphere –Stratosphere: T  with altitude –Troposphere: T  with altitude  Cloud layers ~ Uranus –< 1 bar: CH 4 clouds –1-5 bars: NH 3 & H 2 S clouds –>5 bars: NH 3, NH 4 SH, H 2 S, H 2 O clouds –>50 bars: H 2 O ice clouds (T = 0  C)  Pressure: 1-3 bars  Composition: –85% H, 13% He, 2% CH 4  At high altitudes –80% H, 19% He –Blue color due to absorption of red light by methane  Atmosphere divided ~ Uranus –Thermosphere –Stratosphere: T  with altitude –Troposphere: T  with altitude  Cloud layers ~ Uranus –< 1 bar: CH 4 clouds –1-5 bars: NH 3 & H 2 S clouds –>5 bars: NH 3, NH 4 SH, H 2 S, H 2 O clouds –>50 bars: H 2 O ice clouds (T = 0  C) Images from:

Storms & Climate  Winds blow westward –Opposite from planet’s rotation  Winds up to 2000 km/hr –Near Great Dark Spot  Mean cloud T: -193 to -153  C  Great Dark Spot –Counterclockwise  Small Dark Spot  Scooter –Orbits every 16 hours  Winds blow westward –Opposite from planet’s rotation  Winds up to 2000 km/hr –Near Great Dark Spot  Mean cloud T: -193 to -153  C  Great Dark Spot –Counterclockwise  Small Dark Spot  Scooter –Orbits every 16 hours Image from: Images from: Great Dark Spot Small Dark Spot Great Dark Spot Small Dark Spot Scooter

Magnetic Field  1.42 µT = G –Much stronger than Uranus’ magnetic field  Uranus: G  Tilted 47  from rotation axis –Uranus tilted 59   Offset 0.55 radii from center of planet –Uranus offset ~0.33 radii from center  Probably due to internal flow of mantle –Convective movement of liquid mantle –~ Uranus  1.42 µT = G –Much stronger than Uranus’ magnetic field  Uranus: G  Tilted 47  from rotation axis –Uranus tilted 59   Offset 0.55 radii from center of planet –Uranus offset ~0.33 radii from center  Probably due to internal flow of mantle –Convective movement of liquid mantle –~ Uranus

Rings  4 distinct rings –Very narrow & faint  Composed of dust from meteorite impacts of moons  Contain bright arcs  Twisted structure  4 distinct rings –Very narrow & faint  Composed of dust from meteorite impacts of moons  Contain bright arcs  Twisted structure Images from:

Heat Output  Receives 40% of Sunlight as Uranus –Yet have similar surface T’s  Radiates 2.6x as much as receives from Sun –Generates 161% as solar input –Uranus only radiates 1.1x as much  Possible sources: –Radiogenic heating –Dissociation of methane into H-C chains –Convection in lower atm, causing gravity waves  Receives 40% of Sunlight as Uranus –Yet have similar surface T’s  Radiates 2.6x as much as receives from Sun –Generates 161% as solar input –Uranus only radiates 1.1x as much  Possible sources: –Radiogenic heating –Dissociation of methane into H-C chains –Convection in lower atm, causing gravity waves

Moons  At least 13 moons  Shepherd Moons **  Larissa –Irregular, heavily cratered & probably rubble pile  Proteus –As large as can be w/o being spherical  Triton **  Nereid –Diameter: 340 km –Most eccentric orbit of any moon  e = 0.75  At least 13 moons  Shepherd Moons **  Larissa –Irregular, heavily cratered & probably rubble pile  Proteus –As large as can be w/o being spherical  Triton **  Nereid –Diameter: 340 km –Most eccentric orbit of any moon  e = 0.75 Images from: Image from:

Shepherd Moons  Irregular & probably rubble piles  4 moons inside rings –Naiad (29 km radius) –Thalassa (40 km radius) –Despina (74 km radius) –Galatea (79 km radius)  Irregular & probably rubble piles  4 moons inside rings –Naiad (29 km radius) –Thalassa (40 km radius) –Despina (74 km radius) –Galatea (79 km radius) Images from: Simulated image of Despina Simulated image of Galatea Simulated image of Thalassa Naiad or Thalassa from Voyager 2

Triton  Diameter: km –7th largest in Solar System  Eccentricity:  Density: 2.14 g/cm 3 –Composition ~ Pluto  Retrograde orbit –Probably captured KBO –Spiraling downward  Tenuous nitrogen atm  Geologically active –Geysers of nitrogen  Diameter: km –7th largest in Solar System  Eccentricity:  Density: 2.14 g/cm 3 –Composition ~ Pluto  Retrograde orbit –Probably captured KBO –Spiraling downward  Tenuous nitrogen atm  Geologically active –Geysers of nitrogen Images from: Bluish streaks = N geysers Red Southern Polar Cap Cantaloupe Terrain

Summary  Neptune ~ Uranus –Size, composition, atmosphere, magnetic field  Neptune different from Uranus –Heat output, fewer moons, active atmosphere  Moons –Small inner shepherd moons:  Irregular & probably rubble piles –Triton:  Cryovolcanism, composition ~Pluto, decaying orbit –Nereid:  Most eccentric orbit  Neptune ~ Uranus –Size, composition, atmosphere, magnetic field  Neptune different from Uranus –Heat output, fewer moons, active atmosphere  Moons –Small inner shepherd moons:  Irregular & probably rubble piles –Triton:  Cryovolcanism, composition ~Pluto, decaying orbit –Nereid:  Most eccentric orbit Images from: Image from: