Astronomy 301 - Mon. Oct. 4Guest lectures, today and Wednesday:Prof. Harriet DinersteinLast Friday: Overview of the Solar System,surfaces of terrestrial planetsToday: processes affecting surfaces of theterrestrial planets, general properties of Jovianplanets, and moons that are nearly planetsTerrestrial vs. Jovian PlanetsHow do terrestrial planets differ from Jovian ones?Are there properties that only terrestrial planets have?Are there properties that only Jovian ones have?Properties of Terrestrial PlanetsSurfaces: features, processes that cause changeAtmospheres: gases present, thickness (will bediscussed in much more detail next week, ch. 10)Interiors: what they’re made of, conditions thereHow do we learn about these, for remote planets?Processes on Planetary Surfaces• Impact craters: caused when objects from space crash;craters with central peak, crater walls, “rays”.• Vulcanism: the upwelling of lava (hot molten rock),produces conical volcanos, or broad flows that repavethe surface. They also “erase” previous impact craters.• Erosion: the slow wearing-down of surface features.What agents can you think of, that cause erosion onthe Earth? What about on the Moon?Planetary Interiors• How do we know what planets are made of, inside?Major clue: average densityWhat do we need to know, in order to get the density?Volume of a sphere:Averaged density:! Vol =4"R33! "=MassVol=Mass43( )#R3Average Densities of Planets~ 5000 kg m-3Earth’s interior3000 kg m-3Earth’s crust2000 kg m-3concrete1000 kg m-3waterPlanetary Magnetic FieldsGlobal magnetic fields arise from moving electrical chargesthat produce a magnetic field; need a rotating liquid core.(This is another clue about the interior composition!)Properties of Jovian PlanetsSurfaces: cloud layers, bands, “spots”Interiors: what they’re made of, conditionsCompanions: satellite systems, ringsCloud layers create the visible “surface”Rapid rotation stretchesatmospheric structures into bands.Because they are gaseous, theycan show “differential rotation,”which means the rotation period isdifferent for different latitudesSolid-Body Rotation (e.g. the Earth)! Rotational Velocity =2"RPeriodPeriod is the samefor all locations(latitudes), but thevalue of R changeswith latitude!Locations at higherlatitudes don’t travelas far, so theirspeed is slower.The “Great Red Spot” - long lived cyclonePlanetary Rings: Rings of SaturnThe rings are not solid, butmade of small. icy bodies.How do we know this?differential rotation;changing view of the ringsUranus’ Rings were discovered whenthey “eclipsed” background stars…of rings and Roche Limits: the locationwhere tidal forces shred bodiesJupiter’s moonscan be thought ofas “worlds” inthemselves,especially theGalilean satellitesof Jupiter.• Io: Active volcanoes (the “pizza” moon)• Europa: Possible subsurface water ocean• Ganymede: Largest moon in solar system• Callisto: A large, cratered “ice ball”Yet More Worlds: Jovian moonsMajor Satellites of the Solar
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