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Astronomy Notes Moons of Jovian Planets.docx

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Astronomy 1021
Trevor Kirsh

Astronomy Notes November 28, 2012 This Class: Moons of the Jovian Planets  Jovian Planets have numerous moons o Jupiter: 67 known moons o Saturn: 62 known moons o Uranus: 27 known moons o Neptune: 13 known moons  The Medium and Large Moons o Enough gravity to be spherical o Resemble terrestrial worlds: solid, geology  Some have atmospheres, hot interiors, magnetic fields o Two moons are bigger than Mercury, and four more are bigger than Pluto o Substantial amounts of ice  Jovian Moon Formation o Formed in disks around the planets  Just like how planets formed around the sun o Circular orbits in equatorial plane, generally orbit in same direction as planet is rotating o Almost all have synchronous rotation: tidally locked  The small moons are far more numerous than medium and large moons o Large > 1,500km o Medium: 300-1,500km o Small < 300km  These don’t have enough gravity to become spherical  Maybe captured asteroids or comets, so they don’t follow usual patterns  Jupiter’s Moons o Io  No impact craters  Io has tons of volcanoes  It’s the most volcanically active place in the solar system  Lava plains, shield volcanoes, calderas  Constant resurfacing from the volcanoes, the entire surface is young, not a single impact crater is left  The resurfacing happens from volcanism  Outgassing: sulfur bearing species partly escape, and partly condense and fall back to the surface  Some sulfur-rich volcanoes deposit red, yellow and orange particles back to the surface  Io’s Plasma Torus: the particles blasted out from Io’s volcanoes are ionized, and therefore sometimes get caught up in Jupiter’s magnetic field and create auroras on Jupiter’s poles  Io’s volcanoes are caused by tidal heating: Io is squished and stretched as it orbits Jupiter  The Galilean moons have orbital resonances: every 7 days Io, Europa and Ganymede line up  The gravitational tugs add up over time, this causes the orbit of Io to be so elliptical o Europa  Entire surface is covered by water ice  Many cracks in the ice  Not a lot of impact craters, but a few  Many ridges between huge icebergs  What’s below the icebergs? We think there’s a huge ocean  Europa’s geology is driven by water  For the terrestrial planets, geology was driven by molten rock  For Europa (and some other moons) we see similar activity, but with molten ice instead of molten rock  Example: Cryovolcanism: a cryovolcano is an icy volcano  Europa has a magnetic field, probably caused by the convection in the water  Europa has tidal heating from Jupiter, but not as much as Io
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