Chapter 11 & Chapter 12 Jupiter & Saturn - Northern …€¦ · that emphasizes the relationship of...

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Chapter 11 & Chapter 12Jupiter & Saturn


11.1 Orbital and Physical Properties

11.2 The Atmosphere of Jupiter

A Cometary Impact

11.3 Internal Structure

Almost a Star?

11.4 Jupiter’s Magnetosphere

11.5 The Moons of Jupiter

11.6 Jupiter’s Ring

Units of Chapter 11



This figure shows the solar system from a vantage point that emphasizes the relationship of the jovian planets to the rest of the system


Three views of Jupiter: From a small telescope on Earth; from the Hubble Space Telescope; and from the Cassini spacecraft



• Mass: 1.9 × 1027 kg (twice as much as all other planets put together)

• Radius: 71,500 km (11.2 times Earth’s)

• Density: 1300 kg/m3—cannot be rocky or metallic as inner planets are

• Rotation rate: Problematic, as Jupiter has no solid surface; different parts of atmosphere rotate at different rates – Equator spins faster

• From magnetic field, rotation period is 9 hr, 55 min (9h 50min at equator)



Major visible features:

Bands of clouds; Great Red Spot



• Atmosphere has bright zones and dark belts• Zones are warmer, and are higher than belts• Stable flow, called zonal flow, underlies zones and bands• Simplified model



Real picture is much more complicated

Here: Wind speedwith respect to internal rotation rate



Composition of atmosphere: mostly molecular hydrogen and helium; small amounts of methane, ammonia, and water vapor

These cannot account for color; probably due to complex chemical interactions



No solid surface; take top of troposphere to be at 0 km

Lowest cloud layer cannot be seen by optical telescopes

Measurements by Galileoprobe show high wind speeds even at great depth—probably due to heating from planet, not from Sun



Great Red Spot has existed for at least 300 years, possibly much longer

Color and energy source still not understood



Lightning-like flashes have been seen; also shorter-lived rotating storms

One example: Brown Oval, really a large gap in clouds




Recently, three white storms were observed to merge into a single storm, which then turned red. This may provide some clues to the dynamics behind Jupiter’s cloud movements.


Discovery 11-1: A Cometary Impact

July 1994: Comet Shoemaker-Levy 9, in fragments, struck Jupiter, providing valuable information about cometary impacts


Find that Jupiter radiates more energy than it receives from the Sun:

• Core is still cooling off from heating during gravitational compression

Could Jupiter have been a star?

• No; it is far too cool and too small for that. It would need to be about 80 times more massive to be even a very faint star.



No direct information is available about Jupiter’s interior, but its main components, hydrogen and helium, are quite well understood. The central portion is a rocky core.



Discovery 11-2: Almost a Star?

Jupiter is much too small to have become a star—needs 80 times more mass!

But its energy output was larger in the past; could have been 100 times brighter than the Moon as seen from Earth

Dwarf star in Jupiter’s place probably would have made stable planetary orbits impossible

Jupiter played invaluable role in sweeping solar system clear of debris before too much reached Earth—otherwise life on Earth might not have been possible


Jupiter is surrounded by belts of charged particles, much like the Van Allen belts but vastly larger

Magnetosphere is 30 million km across



Intrinsic field strength is 20,000 times that of Earth

Magnetosphere can extend beyond the orbit of Saturn



63 moons have now been found orbiting Jupiter, but most are very small

The four largest are the Galilean moons, so called because they were first observed by Galileo:

• Io, Europa, Ganymede, Callisto

Galilean moons have similarities to terrestrial planets: orbits have low eccentricity, largest is somewhat larger than Mercury, and density decreases as distance from Jupiter increases



11.5 The Moons of JupiterJupiter with Io and Europa. Note the relative sizes!


Interiors of the Galilean moons



Io is the densest of Jupiter’s moons, and the most geologically active object in the solar system:

• Many active volcanoes, some quite large

• Can change surface features in a few weeks

• No craters; they fill in too fast—Io has the youngest surface of any solar system object



Orange color is probably from sulfur compounds in the ejecta



Cause of volcanism: Gravity!

Io is very close to Jupiter and also experiences gravitational forces from Europa. The tidal forcesare huge and provide the energy for the volcanoes.



Volcanic eruptions also eject charged particles; these interact with Jupiter’s magnetosphere and form a plasma torus



Europa has no craters; surface is water ice, possibly with liquid water below

Tidal forces stress and crack ice; water flows, keeping surface relatively flat



Ganymede is the largest moon in the solar system—larger than Pluto and Mercury

History similar to Earth’s Moon, but water ice instead of lunar rock



Callisto is similar to Ganymede; no evidence of plate activity



Jupiter has been found to have a small, thin ring

11.6 Jupiter’s Ring



12.2 Saturn’s Atmosphere

12.3 Saturn’s Interior and Magnetosphere

12.4 Saturn’s Spectacular Ring System

12.5 The Moons of Saturn

Dancing Among Saturn’s Moons

Units of Chapter 12



View of rings from Earth changes as Saturn orbits the Sun

Saturn Orbits Differentially, similar to Jupiter.

Equator – 10 hrs 14 min

Higher Latitudes – 10 hrs 40 min

- Why is Saturn the flattest planet? 10% difference between Equatorial and polar diameters


Saturn’s atmosphere also shows zone and band structure,

but coloration is much more subdued than Jupiter’s

Mostly molecular hydrogen, helium, methane, and

ammonia; helium fraction is much less than on Jupiter



12.2 Saturn’s AtmosphereThis true-color image shows the delicate coloration of the cloud patterns on Saturn


Similar to Jupiter’s, except pressure is lower

Three cloud layers

Cloud layers are thicker than Jupiter’s; see only top layer



12.2 Saturn’s AtmosphereStructure in Saturn’s clouds can be seen more clearly in this false-color image


Wind patterns on Saturn are similar to those on Jupiter, with zonal flow



Jupiter-style “spots” rare on Saturn; don’t form often and quickly dissipate if they do




This image shows what is thought to be a vast thunderstorm on Saturn, as well as the polar vortex at Saturn’s south pole.


Interior structure similar to Jupiter’s



Saturn also radiates more energy than it gets from the Sun,

but not because of cooling:

• Helium and hydrogen are not well mixed; helium tends to

condense into droplets and then fall

• Gravitational field compresses helium and heats it up



Saturn also has a strong magnetic field, but only 5% as strong as Jupiter’s

Creates aurorae



Saturn has an extraordinarily large and complex ring system, which was visible even to the first telescopes



Overview of the ring system


A, B, C Rings

- B is brightest

- C is almost translucent

- A is in between in visibility


Ring particles range in size from fractions of a millimeter to tens of meters

Composition: Water ice—similar to snowballs

Why rings?

• Too close to planet for moon to form—tidal forces would tear it apart



Closest distance that moon could survive is called Roche limit; ring systems are all inside this limit



Voyager probes showed Saturn’s rings to be much more complex than originally thought

(Earth is shown on the same scale as the rings)


Small gaps due to moonlets – (only 2 confirmed)



This backlit view shows the fainter F, G, and E rings


Voyager also found radial “spikes” that formed and then dissipated; this probably happens frequently



• Other edges and divisions in rings are also

the result of resonance

• “Shepherd” moon defines outer edge of A

ring through gravitational interactions



Strangest ring is outermost, F ring; it appears to have braidsand kinks



Details of formation are unknown:

• Probably too active to have lasted since birth of solar system

• Not all rings may be the same age

• Either must be continually replenished, or are the result of a catastrophic event



Saturn’s many moons appear to be made of water ice

In addition to the small moons, Saturn has

• Six medium-sized moons (Mimas, Enceladus, Tethys, Dione, Rhea, and Iapetus)

• One large moon (Titan), almost as large as Jupiter’s Ganymede



Titan has been known for many years to have an atmosphere thicker and denser than Earth’s; mostly nitrogen and argon

Makes surface impossible to see; the upper picture at right was taken from only 4000 km away



Trace chemicals in Titan’s atmosphere make it chemically complex




Some surface features on Titan are visible in this Cassini infrared image


12.5 The Moons of SaturnThe Huygens spacecraft has landed on Titan and returned images directly from the surface


12.5 The Moons of SaturnBased on measurements made by Cassini and Huygens, this is the current best guess as to what the interior of Titan looks like


Discovery 12-1: Dancing Among Saturn’s MoonsThe Cassini spacecraft uses multiple “gravitational slingshots” to make multiple close passes around Saturn’s moons. Precise orbits are decided on the fly.


12.5 The Moons of SaturnThis image shows Saturn’s mid-sized moons


• Mimas, Enceladus, Tethys, Dione, and Rhea all orbit between 3 and 9 planetary radii from Saturn, and all are tidally locked—this means they have “leading” and “trailing” surfaces

• Iapetus orbits 59 radii away and is also tidally locked




Surface of Enceladus seems oddly youthful


Masses of small moons not well known

Two of them share a single orbit



Two more moons are at the Lagrangian points of Tethys



• Jupiter is the largest planet in the solar system

• Rotates rapidly

• Cloud cover has three main layers, forms zone and band pattern

• Great Red Spot is a very stable storm

• Pressure and density of atmosphere increase with depth; atmosphere becomes liquid and then “metallic”

Summary of Chapter 11


• Relatively small rocky core (but still about 10x size of Earth)

• Still radiating energy from original formation

• 63 moons, four very large

• Io: active volcanoes, due to tidal forces

• Europa: cracked, icy surface; may be liquid water underneath

• Ganymede and Callisto: similar; rock and ice

Summary of Chapter 11 (cont.)


• Saturn, like Jupiter, rotates differentially and is significantly flattened

• Saturn’s weather patterns are in some ways similar to Jupiter’s, but there are far fewer storms

• Saturn generates its own heat through the compression of “helium raindrops”

• Saturn has a large magnetic field and extensive magnetosphere

Summary of Chapter 12


• Saturn’s most prominent feature is its rings, which are in its equatorial plane

• The rings have considerable gross and fine structure, with segments and gaps; their particles are icy and grain- to boulder-sized

• Interactions with medium and small moons determine the ring structure

• The rings are entirely within the Roche limit, where larger bodies would be torn apart by tidal forces



• Titan is the second-largest moon in the solar system

• Titan has an extremely thick atmosphere, and little is known about its surface or interior

• Medium-sized moons are rock and water ice; their terrains vary

• These moons are tidally locked to Saturn

• Several of the small moons share orbits, either with each other or with larger moons


Chapter 11 & Chapter 12 Jupiter & Saturn - Northern …€¦ · that emphasizes the relationship of...

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Transcript of Chapter 11 & Chapter 12 Jupiter & Saturn - Northern …€¦ · that emphasizes the relationship of...