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Astronomy 2021A/B Lecture Notes - Galilean Moons

Course Code
ASTR 2021A/B
William Fisher

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Jovian Moons
4 Largest Moons of Jupiter were found by Galileo (Galilean Moons)
Saturn’s Largest Moon was found by Huygen
Slide 14: These moons are formed in a smaller but very similar way to how planets were formed
spinning disk of gas and dust
Jovian moons still have rock but because they are further from the Sun, they have ice
Slide 18: Triton might have been caught, and in that process tossed its own moons releasing
excess energy and getting caught in Neptune’s orbits in a backwards direction
Slide 19: We cannot see the back side of the moon since its rotation is synchronized with Earth’s
orbit, causing it to always face us
Slide 21: The axis that the moon is on causes stronger gravitational forces and creates HIGH
tides on BOTH the left side and right side of the Earth
Slide 23: As Earth’s gravity is stronger than the moon, it has caused the moon’s rotation to slow
down and maintain the moon’s “bulge” facing the Earth at all times – Slide 22 shows that the
moon also does that to Earth but because it is weaker, it doesn’t have a locking effect for earth
Slide 29: Io still has volcanism and hasn’t cooled down because of Tidal Heat. It’s elliptical orbit
causes different distances at different cycles around Jupiter so the Budge is always changing.
This constant flexing causes a lot of heat!
o Why is its orbit so elliptical? Because every 7 days, the Galilean moons (Ganymede
Europa and Io) have orbital resonance! This is where they all line up in their orbit. Since
they keep tugging and pulling on each other in the exact same way at the exact same
time, this causes their elliptical orbit. And since Io is the closest with the shortest orbit,
it has more tugs and pulls therefore it has the strongest Tidal Heating
Calisto isn’t part of this so it doesn’t have much tidal heating
Slide 32: The cracks in Europa are because of tidal heating on its ice, but also there are no
craters… this means something must be “repaving” it. Something must flow to keep it “clean”
Slide 45: Since most of our oceans bottom crawlers feed on the dead corpses that drop from the
top that live off of photosynthesis. In Europa, there is 5x less sunlight so will the things at the
top have enough light to die and feed the things at the bottom?
o Possibly can be due to Jupiter’s magnetic field dropping particles onto Europa that may
produce molecules that fuel life
Slide 49: We have better hopes for Europa than for Ganymede in the case of Liquid Oceans
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