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The Outer Planets Cosmic Abundance of Elements Hydrogen H 1 1,000,000 Helium He 2 80,000 Carbon C 6 363 Nitrogen N 7 112 Oxygen O 8 851 Neon Ne 10 117 Sodium Na 11 2 Magnesium Mg 12 32 Aluminum Al 13 3 Silicon Si 14 45 Sulfur S 16 16 Argon Ar 18 1 Calcium Ca 20 2 Iron Fe 26 36 Nickel Ni 28 2 Major Constituents Gas Formula Jupiter Saturn Hydrogen H2 86% 92% Helium He 14% 7% Methane CH4 0.2% 0.2% Ammonia NH3 0.02% 0.02% Water H2O ~0.2% (?) ~0.4% (?) Interiors: Big H2 Atmospheres Jupiter vs Saturn Jupiter’s Ammonia Clouds: Belts: Dark bands Zones: Bright bands Great Red Spot White Ovals The GRS has lived at least 300 yrs. Ovals have been seen to survive tens of years Jupiter’s clouds result from convection. 1) Hot air expands. 2) Lighter than the rest of the air, it rises. 3) As it rises, it cools and condenses forming clouds. 4) When it is cooler than the ambient air, it sinks. Great Red Spot Saturn’s Clouds Uranus Absorption of sunlight at red wavelengths by methane renders the planet blue. Neptune Neptune emits more energy from its interior than does Uranus. This energy drives weather. The colder temperatures cause methane to condense in the upper atmosphere – these are the clouds that we see. Moons Their densities tell us that they are ½ rock & ½ ice. A typical, heavily cratered, terrain. Saturn’s moon, Tethys Jupiter’s Moons Callisto Heavily cratered surface with small areas of spiky landscape. This is hypothesized to be caused by sublimation (vaporization) of ices on surface. Image from the Galileo Spacecraft Ganymede: 1km relief Largest moon ½ of the surface is dark and heavy cratered. The other ½ is younger, less cratered. It appears to be faulted and, at places, depressed. The low areas appear to be subsequently flooded. This grooved terrain indicates recent geological activity. Europa Few craters A terrain containing elements that were recently dislodged can be seen to neatly fit together if rotated and translated in position. Io Io • Images\iovol_vgr.gif What fuels Io? Each time Ganymede orbits once, Europa orbits twice, and Io orbits 4 times. Plumes fountain 500 km above the Surface Io’s surface is almost devoid of craters, for it is being repaved at a rapid rate. The glow of warm lava. A pool of lava (black) covered with sulfur deposits (orange). This is called Tupan Patera after the Brazilian thunder god. Images taken from the Galileo spacecraft. Io is hot Lava flows on Io exceed 1500 K in temperature. Lavas this hot are not sulfur (which would evaporate immediately). This is hotter than present lavas on Earth (1300-1450 K). Instead these lavas are likely ultramafic (rich in Mg and Fe), similar to the lavas that occurred on early Earth. Present hypothesis, a ~100 km thick crust floats on top of a worldwide ocean of magma 800 km deep. Titan: a moon with an atmosphere Home Work Ch.17 DQ: 1, 12 Problem 9 Ch. 21 DQ: 19, 20 Problem 3 Observações da alta atmosfera Composition of Titan’s stratosphere Molecule N2 CH4 H2 CO CH3D C2H6 C2H2 C3H8 C2H4 HCN HC3N CH3C2H C4H2 C2N2 CO2 Abundance 65-98% 2-10% 0.2-0.6% 6-150 ppm 5-180 ppm 13-20 ppm 2-5 ppm 0.5-4 ppm 0.09-3 ppm 0.2-2 ppm 80-250 ppb 4-60 ppb 1-40 ppb 5-16 ppb 1.5-14 ppb Derived from radiative transfer analyses of Voyager, ISO and ground-based data. Titan’s Surface HST images Peter Smith & Co U. of Arizona Oceans? hν H2 CH4 γ + CH4 -> other hydrocarbons Methane in atmosphere is depleted in107 years. Either methane is supplied or we are witnessing Titan at a particular moment in its history. haze Oceans containing methane explain the near saturated tropospheric conditions, provide a source for methane, and don’t require a penchant for being lucky. C2H2 C2H6 Ocean (CH4, C2H6, N2) Flasar et al. Science 221, 55 Lunine et al. Science 222, 1229 From the Cassini Huygen’s Website 15 15 October 1997 Cassini-Huygens spacecraft, on a Titan IV rocket, waiting for takeoff. A perfect takeoff that saved fuel. Testing Cassini (Jet Propulsion Laboratory, California) We can see the main antenna. All the instruments (e.g. the cameras) are covered. Huygens Probe, European Space Agency We can see the shield that protects the instruments against the heat of entry into the atmosphere. In 2005, the desent of Huygen’s into Titan’s atmosphere. At 170 km altitude, Huygens releases the shield and begins measurements. STAY TUNED IN ! Neptune’s Largest Moon: Triton Triton On Triton the main component of the atmosphere, nitrogen, exits in vapor pressure equilibrium. That is, it exists as an ice on the surface and as vapor in the atmosphere, in the same way that water exists as liquid and ice on Earth’s surface and as a gas in the atmosphere. The amount of gas depends on the temperature. Less exists at cooler temperatures. Atmosphere: This is seen on Earth with the condensation of water at dew point. 1.6x10-7 bar 38K Nitrogen Rings Ring particles are ice fragments, 1 cm to 10 m in size, that orbit Saturn. The rings span 70,000 km and are only 20 meters thick! There are many gaps in the rings as well. Jupiter’s Rings Silicate dust, 10,000 times more transparent than window glass. Uranus’ Rings Rings are made of dark material, unlike ice, and postulated to be carbonaceous. The rings are made up of a bunch of narrow rings, separated by larger gaps. Neptune’s Rings Narrow rings of varying density What causes Ring Structure? The interaction of ring particles with moonlets. Cordelia and Orphelia orbit 2000 km on either side of Uranus’ Epsilon Ring. Uranus’ rings and a couple of shepherds Gaps Embedded moonlets can sweep clear a lane much larger than its diameter, thus causing gaps like the Cassini Division. Roche Limit The distance between a planet and 2 particles (m1 and m2) such that: The difference in the gravitation attraction of the inner and outer mass to the planet exceeds the gravitational attraction between m1 and m2 Summary • Giant planets are large gas planets with nearly solar elemental abundances. • They have small ice-rock cores. • Their moons are ½ rock and ½ ice. • Most moons display heavily cratered terrains. Io, Europa, Triton and Titan are exceptions. • All jovian planets sport rings of differing thicknesses, compositions & character. • Titan supports an atmosphere second only to Venus’ (considering bodies with proper surfaces). It is rich with organics, and its origin is unknown. • The Cassini mission to the saturnian system is in route and functioning well.