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: F_grav = - F_Pressure

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: 9^h 55^m 29^s (internal)

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

Jupiter

Average distance form the Sun	5.203 AU
Eccentricity of orbit	0.048
Orbital period (sidereal)	11.86 years
Diameter	142,984 km = 11.209 Earth (equitorial)
Mass	1.899x10²⁷Kg = 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 Jupiter’s magnetosphere can reach 300 million Kelvins!! (hotter than the center of the Sun!!!! (but density is extremely low)

We can measure the “interior or core” rotation rate by measuring the rotation rate of Jupiter’s magnetic field. We observe synchrotron radiation! Radio emission from electrons moving around (accelerated by) Jupiter’s 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 (Kepler’s 3^rd law), verify Kepler’s 3 laws.

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

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

Name	Mean Distance (km)	Sidereal period (days)	Diameter (Km)	Mass (Kg)	Mean Density Kg/m³
Io	421,600	1.77	3630	8.9x10²²	3570
Europa	670,900	3.55	3138	4.9x10²²	2976
Ganymede	1,070,000	7.16	5262	1.5x10²³	1940
Callisto	1,883,000	16.69	4800	1.06x10²³	1860
Moon			3476	7.4x10²²	3340

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 largest satellite 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

Saturn

Average distance form the Sun	9.572 AU
Eccentricity of orbit	0.053
Orbital period (sidereal)	29.37 years
Diameter	120,536 km = 9.449 Earth (equitorial)
Mass	5.685x10²⁶Kg = 95.16 Earth
Average density	687 kg/m³

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

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

Ring System

Saturn has a huge Ring system visible from Earth. Rings consists of rock and icy particles ranging in size from 1 cm to 5 m across. The gaps in the major ring systems are called: Enke's division (in the A ring) and Cassini's division (between the A and B ring).
Other rings - D (innermost), E, F (braided ring) and G rings.
Rings were probably formed by material that would have been a moon, but Saturn's tidal forces either broke it apart or kept it from forming.

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

18 large moon and 31 smaller ones.
Titan - large and has an atmosphere of Nitrogen, but is very cold.
Some of saturn's satellites are Shepherd satellites which keep the rings particles in place.
Mimas - huge impact crater, Enceladus - high albedo, Tethys - leading hemisphere is heavily cratered, trailing hemisphere wispy markings.

Chapter 14. The Outer Worlds

	Uranus	Neptune
Average distance form the Sun	19.194 AU	30.066
Eccentricity of orbit	0.0429	0.010
Orbital period (sidereal)	84.009 years	164.86 years
Diameter	51,118 km = 4.007 Earth (equatorial)	49,528 km = 3.883 Earth (equatorial)
Mass	8.682x10²⁵Kg = 14.53 Earth	1.024x10²⁶Kg = 17.15 Earth
Average density	1318 kg/m³	1638

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.

Miranda (Uranus) - heavily cratered.
Triton (Neptune) - retrograde orbit - it is spiraling into the Neptune and will collide with it several million years in the future.

Pluto

Pluto

Average distance form the Sun	39.537AU
Eccentricity of orbit	0.2501
Orbital period (sidereal)	248.6 years
Diameter	2,300 km = 0.18 Earth (equitorial)
Mass	1.3x10²²Kg = 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!).

We know little about Pluto
It does have a Moon, Charon which is fairly large compared to the planet itself.
mixture of rock and ice

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

· ASTEROIDS HAVE AND WILL AGAIN STRIKE EARTH!

Meteors:

· 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 isn’t 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)