Study Guide for Test #4

Dr. J. R. Webb

Solar Astronomy



Chapter 12.Jupiter and Saturn: Lords of the Planets.


††††††††††† Physics of Gaseous Planets: Hydrostatic Equilibrium:Fgrav = - FPressure

††††††††††††††† everywhere in the planet.(natural state without rotation is Speherical!).


††††††††††† The difference between gaseous giant planets and stars:Stars high enough

†††††††††††† temperatures and densities in their cores to undergo nuclear fusion and generate

†††††††††††† energy, planets do not!


††††††††††† Gaseous planets rotate Differentially, i.e. different latitudes rotate at different

††††††††††† rates. Divide the star up into concentric cylinders and each cylinder ratates at a

†††††††††† different speed, the innermost cylinder rotates more slowly.


††††††††††† Rotation period of Jupiter: 9h 55m 29s (internal)

†††††††††††††††††††††††††††††††††††††††††††††††††††††† 9h 50m 28s (equitorial)



Average distance form the Sun

5.203 AU

Eccentricity of orbit


Orbital period (sidereal)

11.86 years


142,984 km = 11.209 Earth (equitorial)


1.899x1027 Kg = 317.8 Earth

Average density

1326 kg/m3


Jupiter probably formed by a two step process:

1) accretion of ice-coated dust grains,

2) gravitational attraction of hydrogen and helium gas.


Chemical composition of Jupiter by mass:atmosphere: 75% H, 24% He, 1% else

††††††††††††††††††††††† ††††††††††††††††††††††† ††††††††††††††††††††††††††† Overall: 71% H, 24% He,5% else


Pictures reveal large amount of structure in the Jovian atmosphere.Dark and light lanes are cloud tops at different levels.Spots are hurricanes, the red spot being the most famous and spectacular.Atmosphere has methane (CH4) and ammonia (Nh3) in spectrum.


Internally Jupiter has a solid rocky core, a liquid metallic hydrogen region, then a molecular hydrogen region.


Dynamo process requires free electrons (molten metal + rapid rotation to generate the field).Jupiter has both fast rotation + large liquid metallic hydrogen region = large magnetic field.

Temperatures inside Jupiterís magnetosphere can reach 300 million Kelvins!! (hotter than the center of the Sun!!!! (but density is extremely low)


We can measure the ďinterior or coreĒ rotation rate by measuring the rotation rate of Jupiterís magnetic field.We observe synchrotron radiation!Radio emission from electrons moving around (accelerated by) Jupiterís rotating magnetic field!



Chapter 13.The Galilean Satellites of Jupiter.


The four Galilean Moons of Jupiter:Io, Europa, Ganymede and Callisto were first observed by Galileo.They were used to calculate the speed of light, determine the mass of Jupiter (Keplerís 3rd law), verify Keplerís 3 laws.


The Galilean Satellites are bright enough to see through small telescopes from Earth.


The Galilean Satellites of Jupiter (+ Earth's Moon)


Mean Distance (km)

Sidereal period (days)





Mean Density

































The formation of the Jovian system paralleled the formation of our Solar System; it is a solar system within a solar system!


Voyager discover a total of 63 Jovian satellites plus a ring system!


Io -Io is the innermost Galilean Moon and is covered with sulfur from currently active volcanoes.The volcanoes are powered by Jupiter's gravitational Tidal forces which heat up Io's interior.Continual repaving of the surface, so no long-term structures are present.

Io torus consists of ionized gas or plasma which circles Jupiter in Io's orbit and is caused by the interaction of Jupiters magnetic field and the volcanic eruptions.


Europa - Smoothest body in the Solar system. No mountains, no deep craters, only cracks.Surface is almost pure water ice.Interior is more dense, with a small iron core, rocky mantle, and an ocean of perhaps liquid water underneath the frozen surface.


Ganymede and Callisto -Ganymede is the largestsatellite in the Solar system, and is larger than the planet Mercury.Young light terrain and older dark terrain on its surface.†† Ganymede is highly diferentiated, has a giant dark circular area called Galileo Regio, and has a large metallic core surrounded by a roky mantle.This is covered by a thick layer of ice.Callisto is heavily cratered with large raters, and few small craters.Callisto's surface is darker than Ganymede.


Chapter 12-Continued. The Spectacular Saturnian System




Average distance form the Sun

9.572 AU

Eccentricity of orbit


Orbital period (sidereal)

29.37 years


120,536 km = 9.449 Earth (equitorial)


5.685x1026 Kg = 95.16 Earth

Average density

687 kg/m3



Rotation period of Saturn: 10h 39m 25s (internal)

†††††††††††††††††††††††††††††††††††††††††† 10h 13m 59s (equatorial)


Ring System


Saturn's internal structure is similar to Jupiter's:A region of liquid metallic Hydrogen, but Saturn's inner core is larger in proportion than Jupiters.


Saturn's atmosphere seems to be deficient in Helium, as compared to Jupiter!Also Saturn is radiating a lot more energy than it should be.Both of these mysteries were solved when it was realised that:The helium condenses and rains down on the core, releasing gravitational energy!


Saturn's Moons




Chapter 14. The Outer Worlds





†††††† Uranus

†††††††††† Neptune

Average distance form the Sun

19.194 AU

††† 30.066

Eccentricity of orbit


†† 0.010

Orbital period (sidereal)

84.009 years

†† 164.86 years


51,118 km = 4.007 Earth (equatorial)

†† 49,528 km = 3.883 Earth (equatorial)


8.682x1025 Kg = 14.53 Earth

1.024x1026 Kg = 17.15 Earth

Average density

1318 kg/m3




Uranus was discovered by William Herschel in 1781 by a chance sighting.Neptune was found when astronomers attempted to find a planet which was perturbing Uranus's orbit.


Both planets have similar internal structures, Rocky core, liquid ices mantle,and a outer layer if liquid hydrogen and Helium. No liquid metallic hydrogen regions! Both planets have atomspheres and Rings.Both planets have magnetic fields that are not parallel with the rotational axis or centered on the geometrical center of the planet!


Uranus is tipped over and rotates nearly in the ecliptic plane!Uranus has virtually featureless atmosphere, whereas Neptune has atmosphere details like white clouds, bands and cyclones.


Uranus has 27 satellites, and Neptune has 13 confirmed satellites.






Average distance form the Sun


Eccentricity of orbit


Orbital period (sidereal)

248.6 years


2,300 km = 0.18 Earth (equitorial)


1.3x1022 Kg = 0.0021 Earth

Average density

1900 kg/m3


Pluto was discovered because astronomers were looking for the cause of perturbations in Neptune's orbit (actually there were no perturbations, but thye found Pluto anyway!).




Chapter 15. Vagabonds of the Solar System.


The most important thing about these objects is that they hold clues to the creation of the Solar system since most of the material was never incorporated or altered in planets!!!


Bode's Law - a mathematical method for remembering the distance to the planets actually predicted a planet between the orbit of Mars and Jupiter! (no physics here though).Asteroids (sometimes called Minor planets) were found there.Thousands of asteroids orbit between 2 and 4 AU, 100,000 bright enough to be seen from Earth.†††


Asteroids are primarily metallic and rocky chunks of debris that never were incorporated into a planet, or were broken off from planets.


Gaps in the astroid belt, Kirkwood gaps, are due to Jupiter's gravity and resonances.


Asteroids are also found outside of the asteroid belt!!

        Trojan asteroids - in Jupiter's orbit

        Amor asteroids - Asteroids that cross Mars' orbit

        Apollo asteroids - Asteroids that cross Earth's orbit





        meteoroids - chunks of rock, metal or cometary material floating through the Solar system.

        meteors - What we see when a meteoroid enters the Earth's atmosphere

        meteorite - leftover meteoroid material that isnít burned up in the Earth's atmosphere.

        Types of meteorites - stony (95%), stony irons (1%), irons (4%).

        Meteor craters on Earth - Barrenger crater in Arizona!


Meteors Showers - occurs when the Earth crosses the orbit of an extinct comet.


Comets - icy-rocky material on highly elliptical or parabolic orbits which occasionally or periodically come into the inner parts of the Solar system.The heated material then out gasses and creates the Coma )surroundingthe nucleus) and the Tail (trails off the comet).


Comet Tail -two types:Dust tail (follows comets orbit),Ion Tail (directed away form the Sun)