Transcript 12. - University of California, Berkeley

Giant Planets
Neptune
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Uranus
Saturn
Jupiter
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Notes:
• Homework due Friday
• Midterm #2: Thursday, April 12
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March 20, 2007
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Terrestrial (Rocky)
Outer 4 Planets: Gaseous Giants
The Solar System
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The “Gas Giants”
• No solid surface.
• Much higher mass & radius.
• Primary gases:
Hydrogen and helium
(like the Sun)
• Rock+Ice Cores:
10-15 Earth-Masses
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Next Lecture:
Moons orbiting the Giant Planets
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Jupiter’s Moon: Io
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• A volcanic explosion
can be seen
silhouetted against
dark space over Io's
brilliant limb. Io
more volcanically
active than Earth.
Jupiter – King of the Planets
Mass = 0.001 solar (318 earths),
Radius = 11.2 Earths,
Density = 1.3 g/cc (1.3 x water)
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Distance: 5.2AU
Orbital Period: 11.8 years
Rotation period: 9.9 hours.
Oblate Spheroid
Saturn
Mass = 95 Earths
Radius = 9.4 Earths
Density = 0.7 x water (floats)
Distance: 9.5 AU
Orbital Period: 29.4 years
Rotation period: 10.6 hours.
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Renowned for its rings, composed of
billions of icy-rocks and icy dust (water
and silicates).
Uranus
Mass = 14.5 Earths
Radius = 4.0 Earths
density = 1.3 x water
Distance: 19.2 AU
Orbital Period: 84 years;
Rotation period: 17.2 hours.
Visible Light
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Infrared Light (Thermal Emission)
Neptune
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Neptune
Mass = 17 Earths
Radius = 3.9 Earths
Density = 1.76 x water
Distance: 30 AU
Orbital Period: 163 years;
Rotation period: 16.1 hours.
Cyclonic storms.
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GIANT PLANETS
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Spacecraft Reconnaisance
1980’s: Voyager 1 & 2
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Camera
Spectrometer
Measures spectral lines:
Chemical composition
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Visit all 4
giant planets
Spacecraft Reconnaisance;
Galileo Spacecraft
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•Launched from Space
Shuttle 1989
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Spacecraft Reconnaisance;
Arrived: 1995
Galileo Spacecraft
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2003:
Dropped into Jupiter’s
Atmosphere:
Measure Chemical
Composition:
98% hydrogen & helium
Plus C, N, O
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• Color Enhancement
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Giant Planet’s Chemical Composition
Mostly Hydrogen and Helium
•Add H to:
C, N, O
C, N, O, H
Chemistry
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Why are the Jovian Planets
Massive and Gaseous (H, He) ?
• They formed beyond the frost line (3 AU) from large, icyrocky planetesimals which were massive enough to…
• Capture H/He far from Sun to form gaseous planets.
• Each Jovian planet formed its own “miniature” solar system.
• Moons formed out of these disks.
Young Solar System
gas & dust
Young Jupiter
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Rotational Distortion
of Planet’s Shape
Centrifugal Force:
Flings material at equator outward
Due to Rotation
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Determining the Density inside a Rotating Planet
Use Motion of Orbiting Satellites
Rotation flattens shape
—> Less pull on satellite at poles
Higher density
toward center
—> Exerts Point-like Grav. Force
Track acceleration of
satellites accurately
—> Density throughout interior
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Inside Jupiter
No solid surface and consists mostly of H & He.
Distinct interior layers, defined by increasing density inward.
• Moving from the surface to the
core:
• temperature increases
• pressure & density increases
• Hydrogen atoms so dense:
Electrons not associated with
any one atom: Free- electrons.
Metallic Hydrogen!
• Jupiter's core is rock & ice: 510 times the mass of Earth.
Controversial.
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Hydrostatic Equilibrium – Pressure balance
“Hydrostatic equilibrium” governs the structure of all planets.
The inside has higher temperature and density because of the weight
of the overlying material.
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Inside Jupiter
• Jupiter emits almost twice as much energy as it absorbs from the Sun.
• accretion, differentiation, radioactivity can not account for it
• Jupiter must still be contracting
• Jupiter has 3 x more mass than Saturn, but is only slightly larger in radius!
• the added weight of H & He compresses the core to a higher density
• like stacking pillows
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• If Jupiter had 10x its mass,
it would have same radius !
Add even more mass, and
Jupiter would get smaller !
• Jupiter is about as large as a
planet can get.
• Uranus & Neptune have
less mass than Saturn, yet
• they have higher
densities
Inside the Jovian Planets
• All Jovian cores appear to be similar.
• made of rock, metal, and Hydrogen compounds
• 10 x the mass of Earth
• Uranus & Neptune captured less gas from the Solar nebula.
• accretion of planetesimals took longer
• not much time for gas capture before nebula was cleared out by Solar wind
• Only Jupiter and Saturn have high enough pressure for H & He to
exist in liquid and metallic states.
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Altitude above clouds tops (km)
Jupiter’s Cloud Layers
• Convection in the troposphere causes
Jovian weather.
• Warm gas rises to cooler altitudes,
where it condenses to form clouds.
• Three gases condense in the Jovian
atmosphere:
• ammonia (NH3)
• ammonium hydrosulfide (NH4SH)
• water (H2O)
• They condense at different
temperatures, so their clouds form at
different altitudes.
Temperature
(C )
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The Jovian Atmospheres
• The temperature profile of each
planet determines the color of its
appearance.
• Cloud layers form where a particular
gas condenses.
• Saturn has the same cloud layers as
Jupiter.
• they form deeper since Saturn is
colder overall
• they are spread farther apart since
Saturn has lower gravity
• Uranus & Neptune
• cold enough to form methane clouds
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Winds of Jupiter’s Bands
Red Spot
in Southern
Hemisphere
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Great Red Spot
A cyclone the size of the Earth that
has lasted at least 300 years.
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Jupiters’s Red Spot
Huricane has
lasted 300 years
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Cyclonic Motions
Southern
Hemisphere
Northern
Hemisphere
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Coriolis effect +
motion to/from
low/high P area
Jovian Storms
• We also see high pressure storms
• analogous to hurricanes, but they rotate in the opposite direction
• Jupiter
• the Great Red Spot
• we are not sure why it is red
• Neptune
• the Great Dark Spot
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Neptune’s
Storms
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scooter
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Magnetic Fields
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Jupiter's Magnetosphere
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•
Ion and neutral mass spectrometer
instrument on the Cassini spacecraft,
makes the huge magnetosphere
surrounding Jupiter visible. The
magnetosphere is a bubble of charged
particles trapped within the magnetic
environment of the planet. In this picture,
a magnetic field is sketched over the
image to place the energetic neutral atom
emissions in perspective.
•
Also shown for scale and location are the
disk of Jupiter (black circle) and the
approximate position (yellow circles) of
the doughnut-shaped torus created from
material spewed out by volcanoes on Io,
one of Jupiter's large moons.
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Jupiter’s Magnetosphere –
Bigger than the Sun
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Jovian Magnetospheres
• Saturn, Uranus, & Neptune have smaller & weaker magnetospheres.
• fraction of electrically conducting material in interiors is smaller
• Solar wind is weaker farther out, or else their magnetospheres would be even smaller
• we can not explain the magnetic field tilts of Uranus & Neptune.
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The high energy particles come down the field lines and hit the
atmosphere near the poles, causing the gases to glow. Just like on
the Earth, this makes an “aurora” in a ring-like zone.
Auroral Zones
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The 4 “Jovian” Worlds
• Major features :
Massive: 14 - 300 x mass of Earth
Gaseous: Hydrogen and Helium
Rotating Fast: 10 hours (squashed shape)
Rocky Core (Si, O, Fe, Ni …)
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Ring Systems of the Giant Planets
• Rings made of icey dust
particles
• Compared to Saturn, the
other ring systems:
• have fewer particles
• are smaller in extent
• have darker particles
• Other unsolved mysteries:
• Uranus’ rings are eccentric
and slightly tilted from its
equatorial plane.
• Neptune has partial rings.
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