Transcript PowerPoint Presentation - AST121 Introduction to Astronomy

The Jovian Planets
Chapter 7
Topics
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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
Terrestrial
Distance from the Sun
Jovian
Terrestrial
Jovian
small--1/100 radius large --1/10 radius
of the Sun
of the Sun
orbit at 0.4 to 1.5 orbit at 5 to 30
AU
AU
few
none
rocks and metals
many (# growing)
all have rings
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?