Transcript The Outer Worlds - Stockton University

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
Inner Planets
– Earth
– Mars
– Jupiter
– Saturn
Outer Planets
– Uranus
– Neptune
My Very Excellent Mother Just Served Us Nachos
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
Eccentricity
0.048
Orbital period
11.9 yrs
Orbital Radius
5.20 AU
Inclination
1° 18'
Radius
71,492 km
Mass
318
(Earth Masses)
Density
1.33 g/cm³
Escape velocity
57.5 km/s
Rotation
10 hours
Tilt of Axis (Obliquity)
3.08°
Albedo
0.51
Mean 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 Statistics
Eccentricity
0.056
Orbital period
29.5 yrs
Orbital Radius
9.53 AU
Inclination
2° 30'
Size
60,268 km
Mass
(Earth Masses)
95.2
Density
0.69 g/cm³
Escape velocity
35.4 km/s
Rotation
10 hours
Tilt of Axis
26.7°
Albedo
0.50
Mean surface temperature
95 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% 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' Statistics
Eccentricity
0.046
Orbital period
84 yrs
Orbital Radius
19.2 AU
Inclination
46'
Size
25,559 km
Mass
(Earth Masses)
14.6
Density
1.56 g/cm³
Escape velocity
21.9 km/s
Rotation
18 hours
Tilt of Axis
98°
Albedo
0.66
Mean surface temperature
60 K
Spring Storms on Uranus
Neptune
Neptune's Statistics
Eccentricity
0.010
Orbital period
165.1 yrs
Orbital Radius
30.1 AU
Inclination
1.8°
Size
24,764 km
Mass
(Earth Masses)
17.3
Density
2.27 g/cm³
Escape velocity
24.4 km/s
Rotation
24 hours
Tilt of Axis
29.6°
Albedo
0.62
Mean surface temperature
60 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
Jupiter
Saturn
Uranus
Neptune
Composition
Gaseous
Liquid hydrogen
Metallic hydrogen
Rock – metal core
Gaseous
Liquid hydrogen
Metallic hydrogen
Rock – metal core
Gaseous
Liquid hydrogen
H2O, CH4, NH3
Rock?
Gaseous
Liquid hydrogen
H2O, CH4, NH3
Rock?
Differentiated
Yes
Yes
Yes
Yes
Atmosphere
75% Hydrogen
24% Helium
75% Hydrogen
24% Helium
Methane
Methane
Magnetic Field
Enormous!
Large
Large
Large
# Moons
60t
30
23
8
1
7 (major)
Thousands
(minor)
8
7 (ring arcs)
# Rings
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
–
–
–
•
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 generates enormous
magnetic field
Tilted 10° to rotation axis
Io produces a small “hole” in magnetic field
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
Mercury
Venus
Mars
More Sizes