The Jovian Planets

Chapter 7

Topics

• Jupter, Saturn, Uranus, Neptune

• How do we know?

• Why do we care?

• What is common about the outer planets?

• What is peculiar to each of these planets?

Jovian planets (Jupiter-like)

Size

radius is about 1/10 of the radius of the Sun

Distance from the SunT

erre

stri

al

Jovian

Terrestrial Jovian

small--1/100 radius of the Sun

large --1/10 radius of the Sun

orbit at 0.4 to 1.5 AU

orbit at 5 to 30 AU

few many (# growing)none all have rings

Size

Location

Moons

Rings

Compositionrocks and metals gasses and ice

Composition

0.71 to 1.67 g/cm3

So what are they made of?

mostly gasses (hydrogen, helium) and ice

Jupiter

• largest planet

• Great Red Spot

• studied by Pioneer, Voyager 1 & 2, Galileo spacecraft

• liquid interior (very high pressure and temperature)

• 16 moons (4 largest are the Galilean moons)

Io

• Active volcanoes

Europa

• subsurface ocean• cracked ice

Ganymeade

• lots of faults• strong magnetic field

Callisto

• old surface (meaning that it’s not undergoing lots of change except for impact craters)

Saturn

• Large, thin rings

• Rings are held together by the gravitational attraction of “shepharding” satellites

• Major Gaps: The Cassini and Enke divisions

Titan

• larger than Mercury• has an atmosphere• probably has oceans of

methane

Uranus

• discovered in 1781• shows no cloud banding• axis of rotation is only

tilted 8 degrees from the ecliptic

• 84 year orbital period• rings originally discovered

during occultation of a star

• young rings (what’s the source of dust?)

Neptune

• noted by Galileo

• the exact path of Uranus could not be explained by the gravitational pulls of the Sun, and the other planets. What does this mean?

• discovered in 1846

• 164 year orbital period

• strong magnetic field

Triton

• density 2.1 g/cm3

• atmosphere (nitrogen)• impact craters due to

comets• ice made of water• active ice volcanoes• retrograde orbit (it’s going

the wrong way)• probably captured by

Neptune

Extrasolar planets

• How many planets have we discovered besides those in our solar system?

• I’m starting to lose count, but it’s now over 100.• Planets are even found in binary star systems.• We analyze the wobble in a star by studying the

Doppler shift in its spectrum and determine the approximate masses and distances of the orbiting planets.

How do we know?

• How do we know that the outer planets are mostly gas and mostly made up of hydrogen and helium?

• How do we know that the atmosphere of a planet has methane?

• How do we know the period of rotation of the outer planets? (Note: we use a different technique of measuring rotational period of the terrestrial planets.)

• How do we know that a moon’s surface is ice?• How do we know the size of matter within the rings?• How do we know that a moon has an “old” surface and

that the moon has little geologic activity?