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Download The Jovian Planets Sizes of Jovian planets compared to the Earth
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The Jovian Planets Jupiter Saturn Outline Uranus Neptune • Low Density • Small “Core”/Atmosphere Ratio • Rings • Many Natural Satellites Spacecraft Missions to the Jovian Planets Four Major Missions • Pioneers 10 & 11 (launched 1972) • Voyagers 1 & 2 (launched 1977) • Galileo (launched 1989) • Cassini-Huygens (launched 1997) Difficulties/Issues with sending probes to Jovian planets • Energy source: solar panels + internal radioactive generators needed • Distance from Earth: autonomous • Destruction of spacecraft by debris: asteroids, rocks, etc. • Trajectory: gravity assisted • • • • • • • • • • Spacecraft Missions to Jovian Planets General Properties of Jovian Planets Properties of Jupiter & Saturn Equatorial bulges Internal heat sources Galileo Probe & Jovian atmospheric structure Belts & Zones The Great Red Spot Rings Voyagers Sizes of Jovian planets compared to the Earth Properties of Jupiter • Composition: 75% hydrogen, 24% helium + methane, ammonia, water ice… • Average Distance from the Sun: 0.7 light hours = 5.2 AU • Rotation Rate 9h55m30s – Magnetic Field 9h50m30s – Equatorial Clouds 9h55m41s – High Latitude Clouds Note: Hydrogen and Helium • Orbital Period: 11.9 Earth are colorless. years • Axis Tilt: 3.1° • Number of Moons: ~ 61 The Jovian planets have equatorial bulges • Rotation Rates ~ 10-17 hours • Gravity makes planets spherical • Rotation makes planets bulge at the equator (Note: This keeps rings/satellites aligned with equator) Properties of Saturn • Average Distance from the Sun: 1.3 light hours = 9.5 AU • Rotation Rate 10h39m24s – Magnetic Field 10h14m – Equatorial Clouds 10h40m – High Latitude Clouds • Orbital Period: 29.5 Earth years • Axis Tilt: 27° (i.e., Seasons: Note: tan “smog” that overlies UV + Methane → Ethane in clouds below gives Saturn its the Summer color. • Number of Moons: ~ 31 • Equator is 10% wider than pole-to-pole Jupiter & Saturn are about as large as planets can be Internal Heat Sources Jupiter & Saturn radiate twice as much heat as they receive from the Sun • Earth radiates 0.005% as much energy as it receives from the Sun Source of heat from Jupiter is the slow contraction of the planet • Gravitational potential energy → kinetic energy → thermal energy Jupiter A brown dwarf is an object greater than about 13 Jupiter masses, but less than 80. So it is bigger than Jupiter, but smaller than a star. It does not fuse hydrogen, but it can fuse deuterium (proton+neutron nucleus). Source of heat from Saturn is Helium rain • At lower temperature & pressure of Saturn, liquid helium does not dissolve with liquid hydrogen • Deficit of Helium relative to Hydrogen has been measured in the outer atmosphere of Saturn 1995: Galileo probe dropped into Jupiter’s atmosphere Probing Jupiter’s Atmosphere – The Galileo Probe (video) (UV) Troposphere: turbulent clouds due to the Greenhouse effect Jovian Atmosphere Comparison cold enough for water to condense, etc… Internal structure of Jupiter • Note: The behavior of Hydrogen & Helium at high temperatures & pressures is not well understood Belts & Zones • Strong Coriolis forces divide circulation cells into bands • Convection results in bands of different color - Zones: rising, cooling air out of which ammonia condenses into clouds - Belts: falling air depleted in clouds; allows clouds below to be seen The Great Red Spot • Storm that has persisted for at least 300 years • Size: twice as wide as the Earth • Why are such storms so long-lived? → No solid surface to sap away energy (as happens on the Earth) Rings • Composition: mixture of rocks of varying sizes comprised mostly of water ice (high albedo) • Dimensions of Saturn’s rings: 270,000 km x 10s of meters • Roche zone: tidal forces ~ binding gravitational forces • Note: smaller rocks are held together by gravitational & electrostatic forces, & thus can survive Jupiter’s Rings • Jupiter’s rings are less prominent than Saturn’s • Why? Smaller particles Features in Rings • Gaps are present in the rings. They are created by Gap Moons that nudge particles out of particular orbits • Spokes: particles levitated out of ring plane by forces associated with the magnetic fields Origin of Rings • Roche zone: within 2 to 3 planetary radii of any planet, the tidal forces on an object are comparable to the force of gravity holding it together • Tidal forces could, in principle, rip a moon apart, or keep a moon from forming Origin of Rings • Theory 1: a large moon strayed too close to its planet as a result of an impact. Problem: such an unlikely event would have to have happened to all of the Jovian planets • Theory 2: they formed from leftover chunks of rocks and ice that condensed into a disk of gas around the planet. Problem: these chunks would been ground down in size by impacts with small dust particles that orbit the Sun. The ground up remains would have lost angular momentum from pressure from sunlight, and they gradually would have spiraled into the planet Origin of Rings Enceladus Juno • Theory 3: the ring particles originate from small moonlets which are being ground up by impacts with dust sized particles, or through occasional impacts with larger objects. • The majority of the ring particles are young and reflective • Continuous replenishment from moonlets • Consequence: the ring may look very different in the future • Arrival date: 4 July 2016 • Goal: Reveal the story of the formation and evolution of Jupiter • … through magnetic fields, atmospheric dynamics and composition. • Stay tuned. http://solarsystem.nasa.gov/missions/juno/indepth Where are the Voyager Spacecraft? Deep Space Network – Antenna locations http://voyager.jpl.nasa.gov • Voyager 1 (137 AU from Sun) & 2 (112 AU) continue to transmit signals back to Earth. • Voyager 1 entered interstellar space in August 2012 • They are continuously monitored by the Deep Space Network • Present Voyager mission – Find the edge of the Solar System (Video) The Golden Record The Golden Record • A Gold-plated phonograph record was placed in each Voyager • Intent: to show the story of Earth to extraterrestrials through sounds and images portraying the diversity of life and cultures of Earth • Record, cartridge and needle are encased in aluminum jacket. Symbolic instructions on origin of spacecraft and directions on how to place the record included • Time till closest approach to another planetary system = 40,000 yrs http://voyager.jpl.nasa.gov/spacecraft/goldenrec.html The Golden Record • Example of included photographs: Solar system parameters (Frank Drake) http://voyager.jpl.nasa.gov/spacecraft/scenes.html http://voyager.jpl.nasa.gov/spacecraft/goldenrec_more.html