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Chapter 8-9

Astronomy 1021 Chapter Notes - Chapter 8-9: Galilean Moons, Metallic Hydrogen, Tidal Heating

Course Code
ASTR 1021
Sarah Gallagher

of 3
Astronomy Reading Chapter 8: Jovian Planet Systems
The Four Jovian Planets Include:
o5.20 AU from the Sun
oMass = 318M Earth
oComposition: Mostly H, He
o9.54 AU from the Sun
oMass = 95M Earth
oLow density for size
oComposition: Mostly H, He
o19.2 AU from Sun
oMass = 14M Earth
oComposition: Hydrogen compounds, rock, H and He
o30.1 AU from the Sun
oMass = 17M Earth
oComposition: Hydrogen compounds, rock, hydrogen and helium
In terms of composition you can divide the Jovian planets into two types:
oJupiter and Saturn are gas giants
oUranus and Neptune are ice giants
8.1 A Different Kind of Planet:
Jupiter and Saturn are made almost entirely of hydrogen and helium with just a small
amount of their masses coming from hydrogen compounds
oAll Jovian planets differ primarily in their relative proportions of hydrogen
Their inner compositions are more similar to the Sun than the terrestrial planets
All Jovian planets are thought to have grown from ice-rich planetesimals
The jovian planets farthest from the Sun took longer to form and captured less hydrogen
and helium gas, explaining why Uranus and Neptune have larger proportions of hydrogen
compounds, rock and metal
If you plunged bellows Jupiter’s clouds you would never encounter a solid surface – just
ever-denser and hotter hydrogen/helium compressed into bizarre liquid and metallic
None of the Jovian planets have a solid surface and their layers are different for different
Jovian planets have dynamic winds and weather with colourful clouds and enormous
Clouds of different compositions and colours form, and different compounds condense at
different depths in each planet’s atmosphere
Uranus and Neptune look blue because of methane
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Jupiter’s “Red Spot” is a storm twice as wide as Earth
All off the planets have a magnetosphere similar to Earths, Jupiter's is very strong and a
result of its metallic hydrogen
8.2 A Wealth of Worlds: Satellites of Ice and Rock
The size of Jovian moons rival the smallest planets in size – Jupiter’s Ganymede and
Saturn’s Titan are both larger than Mercury
However, they are not similar in composition because they formed in the cold outer
Small moons are far more numerous than medium and large moons
Jovian Moons:
Jupiter is home to the four Galilean moons (discovered by Galileo) which are listed
Galilean moons have orbital resonances: every 7 days Io, Europa & Ganymede line up
Some Galilean moons are geologically active
Io: The Volcano World
oThe most volcanically active body in our solar system
oAll impact craters have been covered by lava
oIts core should have died a long time ago due to its size however tidal heating
keeps ongoing heat in the core and is the cause of its volcanoes
Constant flexing causes heating
Europa: The Water World:
oEntire surface is covered by water ice (with a lot of cracks in the ice due to tidal
oTidal heating could be a plausible answer for the liquid water on Europa
Ganymede and Callisto:
oLike Europa, both have surfaces of water ice
oGanymede is the largest moon in our solar system and shows evidence of recent
liquid water eruptions and freezing
oCallisto is a heavily cratered ice ball which also shows signs of a liquid
oCallisto is geologically dead
oTidal heating is weak on Ganymede and absent on Callisto which leaves us to
figure out what the heat source is
Saturn’s moon Titan:
oOnly moon with a dense atmosphere, thick atmosphere leads to methane rain and
surprising erosion
oIts colour is due to its atmosphere
oConditions are right for methane and/or ethane rain, rivers & lakes
oHas a greenhouse effect but it is still too cold to our standards
oCassini observations have taught us more about Titan
they display hydrocarbon seas and lakes of liquid methane
Saturn’s other moons:
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oMimas, Enceladus, the smallest geologically active moon in our solar system,
Tethys, Dione, Rhea, lapetus
oMost are cratered ice balls
oOften show evidence for past volcanism/tectonics
Moons of Uranus & Neptune:
oWe know a lot less about these moons but they still show evidence of geological
oTriton is a moon of Neptune, it orbits Neptune backward and shows evidence of
recent geological activity
8.3 Jovian Planet Rings:
Made of countless icy particles ranging in size from dust grains to large boulders each
circling due to Kepler’s laws
All Jovian planets have rings but Jupiter, Uranus and Neptune have smaller, darker ring
Rings and gaps are caused by particles bunching up at different orbital differences
Ring particles cannot last for billions of years so the rings we see today must be made of
particles recently created
oNew particles are continuously being supplied to the rings
oThe source is mostly likely small “moonlets” which have small and large impacts,
both of which provide particles
Chapter 9: Asteroids, Comets, and Dwarf Planets
Chapter 10: Other Planetary Systems:
Extra solar planets are planets that orbit other stars
Detecting extrasolar planets poses a huge technological problem because there is
minimal angular separation, planets are very small compared to their distances apart,
and the star is a billion times brighter and therefore tends to overwhelm any planetary
light that can be captured in a photo
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