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?