Lecture 4: Overview of the Giant PlanetsAstro 202Prof. Jim Bell ([email protected])Spring 2008But first...Turn in Paper 1 nowPaper 2 is “Handed Out” onlinePaper 2 due at beginning of class on Feb. 14Don’t wait until the last minute!This just in from Mercury...MESSENGER ProbeAstro 202 4Jupiter, Saturn, Uranus, Neptune!General properties!Atmospheres!Interiors!Ring SystemsAstro 202 5The “Jovian” PlanetsAstro 202 6Basic Properties of Jupiter•Average Distance from Sun: 778,000,000 km (a=5.20 AU)•Orbital period: 11.86 years; eccentricity: 0.048•Period of Spin around axis: ~10 hours (varies with lat.)•Tilt of Jovian spin axis: 3.1° (no real seasons)•Mass: 1.9x1027 kg = 317 ME ; Radius: 71,400 km = 11 RE•Density = 1.3 g/cm3 (mostly gaseous, small "rocky" core?)•No "surface" like the terrestrial planets: only clouds visible•Gravity = 24.8 m/sec2 (2.5 times Earth's)•Cloud-top temperature: 125 K (-148°C)•Atmosphere: Mostly H, He (plus CH4, NH3, H2O, NH4HS, ...)•Moons: 63 presently known•Rings: Jupiter has an elegant set of thin dark ringsAstro 202 7Observations!Jupiter is a prominent object in the night sky for many months out of each year!Through even a small telescope, Jupiter's clouds appear yellow, red, and brown!And features can be seen– Belts of red clouds– Zones of white clouds– Oval-shaped stormsAstro 202 8Space Missions!7 robotic spacecraft have flown past Jupiter!1 more orbited Jupiter from 1995 to 2003Mission Dates Goals and Results Pioneer 10 1973 First Jupiter flyby; studied magnetic field, cloudsPioneer 11 1974 Flyby; studied magnetic field, atmosphereVoyager 1 1979 Flyby; high resolution imaging and other studiesVoyager 2 1979 Flyby; high resolution imaging and other studiesUlysses 1992 Flyby (Sun gravity assist); solar wind & magnetic fieldGalileo 1995- Orbiter; imaging, spectroscopy, magnetic fields, 2003 and atmospheric entry probeCassini 1999 Flyby (Saturn gravity assist); imaging, spectroscopyNew Horizons 2007 Flyby (Pluto gravity assist); imaging, spectroscopyAstro 202 9 Voyagers 1 and 2!Astro 202 10Jupiter's Dynamic Atmosphere!The zones, belts, and storms change with time!The most famous storm, the Great Red Spot, has been around at least since 1610Jupiter rotationJupiter cloud motions(rotation removed)Astro 202 11Atmospheric Composition!Determined by spectroscopy from telescopes and spacecraft!Directly sampled by the Galileo probe Name Symbol % Volume Hydrogen H2 90 Helium He 4.5 Methane CH4 0.07 Ammonia NH3 0.02 Ethane C2H6 0.01 Deuterated Hydrogen HD 1.8 x 10-3 Water vapor H2O 1 x 10-4 Deuterated Methane CH3D 3 x 10-5 Phosphine PH3 1 x 10-6 Carbon monoxide CO 1 x 10-7 Germanium Tetrahydride GeH3 ? 1 x 10-7 The composition of Jupiter is very close to the composition of the SunGalileo Probe MissionRelease Date: 7/13/95 Entry into Jupiter: 12/7/95Entry Speed: 106,000 mphProbe Data Return: 59 min 3.5 megabitsPenetration depth 200 km (124 mi)Astro 202 12Beltsand ZonesKnowledge of the composition & temp. allows astronomers to create a model to explain the distribution and colors of the belts and zonesAstro 202 13Atmospheric Circulation Great Red SpotAstro 202 14Jupiter's Interior Interior structure is inferred from models and extrapolation of data from the upper cloud layers...Astro 202 15Internal vs. External Heat Sources!Energy Balance – What comes in must go out...– Solar heat absorbed = Outgoing planetary heat!But for Jupiter: Outgoing = 1.8 ! Incoming!Jupiter has a strong internal heat source– Heat stored from planetary contraction?– From some other source?!This has a strong influence on atmospheric circulation and the "climate" of Jupiter– More in Lecture 14...Astro 202 16Giant Planet or Failed Star?!Calculations suggest that Jupiter is about 100 times less massive than needed to initiate hydrogen fusion reactions in its core and become a star. !Since factors of 100 are not so large in astronomy, it is legitimate at some level to view Jupiter as either a very large planet, or as a small failed star.Astro 202 17Jupiter's Magnetic Field!The largest planetary structure in the solar system (apparent size > the full Moon)• Jupiter's magnetic field is about 20,000 times stronger than Earth's• The solar wind is deflected in a huge zone around the planet• Evidence for the magnetic field can be seen in telescope and spacecraft images of auroraeAstro 202 18Satellites &Rings!Galileo discovered the 4 large moons of Jupiter in 1610–We call them the Galilean satellites!12 other smaller moon found: 1872-1979!Dozens more even smaller found since ‘99–Total is now 63! (http://www.dtm.ciw.edu/sheppard/satellites/)!Jupiter also has a faint, thin ring systemAstro 202 19SaturnAstro 202 20The Jovian PlanetsAstro 202 21Basic Properties of Saturn•Average Distance from Sun: 1.43 billion km (a=9.54 AU)•Orbital period: 29.46 years; eccentricity: 0.056•Period of Spin around axis: ~10 hours (varies with lat.)•Tilt of Saturn's spin axis: 26.7° (seasons and tilted rings)•Mass: 5.7x1026 kg = 94 ME ; Radius: 60,270 km = 9.4 RE•Density = 0.7 g/cm3 (mostly gaseous, small "rocky" core?)•No "surface" like the terrestrial planets: only clouds visible•Gravity = 10.5 m/sec2 (1.07 times Earth's)•Cloud-top temperature: 95 K (-178°C)•Atmosphere: Mostly H, He (plus CH4, NH3, H2O, NH4HS, ...)•Moons: 60 presently known•Rings! Billions of icy moonlets all orbiting togetherAstro 202 22Observations!Saturn is the most distant planet that can be (easily) seen without a telescope !Through a small telescope, Saturn's yellow clouds and spectacular rings can be seen!Features in Saturn's atmosphere are much more subtle than in Jupiter'sAstro 202 23Space Missions!3 robotic spacecraft have flown past Saturn!Cassini has been orbiting Saturn since 2004Mission ! Dates! Goals and Results Pioneer 11! 1979! First Saturn flyby; studied magnetic field, cloudsVoyager 1! 1980! Flyby; high resolution imaging and other studiesVoyager 2! 1981! Flyby; high resolution imaging and other studiesCassini! 2004-! Orbiter; imaging, spectroscopy, magnetic fields,! !