General Astronomy

General AstronomyThe Solar System

The Outer Worlds

Many slides are taken from lectures by Dr David Wood, San Antonio College

The PlanetsIn 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

PlanetsWe continue by looking at the Outer

Planets and attempt to categorize their main features:

JupiterSaturnUranusNeptune

The Outer Planets

Jupiter

Jupiter's Statistics Eccentricity 0.048Orbital period 11.9 yrsOrbital Radius 5.20 AUInclination 1° 18'Radius 71,492 kmMass (Earth Masses) 318Density 1.33 g/cm³Escape velocity 57.5 km/sRotation 10 hoursTilt of Axis (Obliquity) 3.08°Albedo 0.51Mean surface temperature

125 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 StatisticsEccentricity 0.056Orbital period 29.5 yrsOrbital Radius 9.53 AUInclination 2° 30'Size 60,268 kmMass (Earth Masses) 95.2Density 0.69 g/cm³Escape velocity 35.4 km/sRotation 10 hoursTilt of Axis 26.7°Albedo 0.50Mean surface temperature

95 K

Saturn’s Storms

Saturn and Tethys

Gas Giant StructureHydrogen 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% H2 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% H2 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' StatisticsEccentricity 0.046Orbital period 84 yrsOrbital Radius 19.2 AUInclination 46'Size 25,559 kmMass (Earth Masses) 14.6Density 1.56 g/cm³Escape velocity 21.9 km/sRotation 18 hoursTilt of Axis 98°Albedo 0.66Mean surface temperature 60 K

Spring Storms on Uranus

Neptune

Neptune's StatisticsEccentricity 0.010Orbital period 165.1 yrsOrbital Radius 30.1 AUInclination 1.8°Size 24,764 kmMass (Earth Masses) 17.3Density 2.27 g/cm³Escape velocity 24.4 km/sRotation 24 hoursTilt of Axis 29.6°Albedo 0.62Mean surface temperature 60 K

Ice Giant StructureHydrogen is converted from is gaseous to its liquid form under pressureCannot create enough pressure for metallic hydrogenAlmost certainly liquid water layers deep in planets…perhaps surrounding the coresDiamond 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 PlanetsJupiter Saturn Uranus Neptune

Composition

GaseousLiquid hydrogen

Metallic hydrogen

Rock – metal core

GaseousLiquid hydrogen

Metallic hydrogen

Rock – metal core

GaseousLiquid

hydrogenH2O, CH4, NH3

Rock?

GaseousLiquid hydrogenH2O, CH4, NH3

Rock?

Differentiated Yes Yes Yes Yes

Atmosphere 75% Hydrogen24% Helium

75% Hydrogen24% Helium Methane Methane

Magnetic Field Enormous! Large Large Large

# Moons 60t 30 23 8

# Rings 17 (major)

Thousands (minor)

8 7 (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– 21st moon discovered in Oct. 2002– 22nd & 23rd 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

VenusMars

Mercury

More Sizes