General Astronomy The Solar System The Outer Worlds Many slides are taken from lectures by Dr David Wood, San Antonio College

The Planets In order of increasing distance from the Sun: –Mercury –Venus –Earth –Mars –Jupiter –Saturn –Uranus –Neptune My Very Excellent Mother Just Served Us Nachos Inner Planets Outer Planets

Planets We continue by looking at the Outer Planets and attempt to categorize their main features: Jupiter Saturn Uranus Neptune

The Outer Planets

Jupiter

Jupiter's Statistics Eccentricity0.048 Orbital period11.9 yrs Orbital Radius5.20 AU Inclination1° 18' Radius71,492 km Mass (Earth Masses) 318 Density1.33 g/cm³ Escape velocity57.5 km/s Rotation10 hours Tilt of Axis (Obliquity)3.08° Albedo0.51 Mean surface temperature125 K

Shoemaker – Levy 9 May 1993 – Carolyn & Eugene Shoemaker, & David Levy find comet with 21 fragments orbiting Jupiter July 20, 1994 – Comet Shoemaker – Levy 9 impacts Jupiter with Fragment “G” leaving a scar larger than Earth in diameter Only impact event ever directly witnessed by human beings

Saturn

Saturn's Statistics Eccentricity0.056 Orbital period29.5 yrs Orbital Radius9.53 AU Inclination2° 30' Size60,268 km Mass (Earth Masses) 95.2 Density0.69 g/cm³ Escape velocity35.4 km/s Rotation10 hours Tilt of Axis26.7° Albedo0.50 Mean surface temperature95 K

Saturn’s Storms

Saturn and Tethys

Gas Giant Structure Hydrogen is converted from is gaseous to its liquid and metallic forms under pressure Galileo probe discovered a liquid water layer in Jupiter’s atmosphere Original seeds of planets form core

Gas Giant Atmospheres Jupiter –Composition is primarily 75% H 2 and 24% He –Galileo probe detected a liquid water layer –We see cloud tops that swirl and change with lightning –Banded structure Belts are dark bands that move vertically downward and horizontally eastward Zones are bright bands that move vertically upward and horizontally westward –Great Red Spot Stable for > 350 years Counter-clockwise rotation in southern hemisphere High pressure system Resides between a belt and a zone and feeds off them Saturn –Composition is primarily 79% H 2 and 19% He –Banded structure with belts and zones but more subdued than Jupiter –Clouds are more spread out and smog in between –Faster equatorial wind speeds than Jupiter (1000 km/hr)

Jovian Atmospheres

Uranus

Uranus' Statistics Eccentricity0.046 Orbital period84 yrs Orbital Radius19.2 AU Inclination46' Size25,559 km Mass (Earth Masses) 14.6 Density1.56 g/cm³ Escape velocity21.9 km/s Rotation18 hours Tilt of Axis98° Albedo0.66 Mean surface temperature60 K

Spring Storms on Uranus

Neptune

Neptune's Statistics Eccentricity0.010 Orbital period165.1 yrs Orbital Radius30.1 AU Inclination1.8° Size24,764 km Mass (Earth Masses) 17.3 Density2.27 g/cm³ Escape velocity24.4 km/s Rotation24 hours Tilt of Axis29.6° Albedo0.62 Mean surface temperature60 K

Ice Giant Structure Hydrogen is converted from is gaseous to its liquid form under pressure Cannot create enough pressure for metallic hydrogen Almost certainly liquid water layers deep in planets…perhaps surrounding the cores Diamond rain or snow? Original seeds of planets form core

Ice Giant Atmospheres Uranus –Still primarily hydrogen & helium –Methane ice crystals provide bluish color –Belts and zones are very faint –Severe seasons due to large axis tilt –Recent Hubble observations show new storms raging as seasons as winter hemisphere sees sunlight Neptune –Surprisingly active –Belts and zones visible to Voyager –Great Dark Spot and Little Dark Spot were/are giant storms –Great Dark Spot vanished between 1989 and 1995 –Highest wind speeds in solar system

Comparing Jovian Planets JupiterSaturnUranusNeptune Composition Gaseous Liquid hydrogen Metallic hydrogen Rock – metal core Gaseous Liquid hydrogen Metallic hydrogen Rock – metal core Gaseous Liquid hydrogen H 2 O, CH 4, NH 3 Rock? Gaseous Liquid hydrogen H 2 O, CH 4, NH 3 Rock? DifferentiatedYes Atmosphere 75% Hydrogen 24% Helium 75% Hydrogen 24% Helium Methane Magnetic FieldEnormous!Large # Moons60 t # Rings1 7 (major) Thousands (minor) 87 (ring arcs) t 21 moons have been discovered in 2003 alone

Jovian Atmospheres Cloud Top

Comparing Jovian Planets Oblateness (flattening) of Jovian planets is due to their rapid rotation.

Obliquity Red line is the ecliptic

Magnetic Fields Jupiter –Metallic hydrogen generates enormous magnetic field –Tilted 10° to rotation axis –Io produces a small “hole” in magnetic field Saturn –Metallic hydrogen generates large magnetic field –Not as large as Jupiter’s field since less metallic hydrogen –Tilted 0° to rotation axis Uranus –Metallic hydrogen is not present, so core compounds generate magnetic fields –Tilted 60° to rotation axis Neptune –Metallic hydrogen is not present, so core compounds generate magnetic fields –Tilted 46° to rotation axis

Moons Jupiter – 60 moons –Galilean Moons are Io, Europa, Ganymede, Callisto –11 moons discovered by Galileo in 2000 Saturn – 30 moons –Titan possesses large atmosphere –Mimas is “Death Star” moon Uranus – 23 moons –Named primarily after Shakespearean characters –Miranda possesses unique geology –21 st moon discovered in Oct –22 nd & 23 rd discovered Sept 2003 Neptune – 11 moons –Triton possesses a weak atmosphere –6 new moons discovered by Voyager 2 in 1989

Rings Jupiter –1 ring –Visible only in backlighting –Discovered in 1979 Saturn –7 major rings –Thousands of minor rings –Radial spokes – still unknown –Discovered in 1600s Uranus –8 thin rings –Discovered in 1977 Neptune –7 minor ring arcs –Discovered in 1989

Sizes Venus Mars Mercury

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