AST 251 Lecture 10

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University of Toronto St. George
Astronomy & Astrophysics

AST 251 Lecture 10 Jovian MoonsFirst discoveries o Four main moons Galileo 1610Io Ganymede Europa and CallistoConfirmation of Keplers heliocentric Solar System modelif moons orbit around Jupiter then it doesnt seem so absurd for the Moon to orbit Earth o Saturns Titan Huygens 1656Jupiters Galilean Moons o Io Ganymede and Callisto larger than the Moon but Europa is almost the same sizeLarge Jovian Moonso Ganymede and Titan larger than Mercury o Several are larger than Pluto o Roundthrough their gravity o Orbit in equatorial plane of hot planet in same direction as planets rotationJovian planets formed as mini Solar Systems from small gaseous disks orbiting the large solar protoplanetary nebula o Exception Triton is on retrograde orbitlikely captured Kuiper belt object like Pluto which orbit intersects with NeptunesComposition of Jovian Moons o Mixture of rocks and ices consistent with solar nebula modelLower temperatures at larger distances o Jupiter Only water iceIce fraction increases with distance to Jupiter Iomostly rock high densityEuropa Ganymede Callistodecreasing density increasing ice fraction o Saturn and beyond Higher proportion of ice than Jupiters moonsAlso methane and other icesCaptured moons of Jovian planets o Smaller satellites appear to be mostly captured planetoids o Odd shapes gravity too weak to force rock into spherical shapeRings o Made of bodies of the size of boulders snowballs and grains o Each Jovian planet has a ringbut Saturns the most prominent o Diameter of rings about 300 000 km o Thickness from 023 kmvery thin structuresProperties of Jupiters large moons
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