The Outer Worlds… • Beyond the orbit of Mars, the low temperatures of the solar nebula allowed condensing bodies there to capture hydrogen and hydrogen-rich gases • This, together with the vast amount of material in the outer Solar System, lead to the creation of the four large Jovian planets – Chapter 10 Jupiter, Saturn, Uranus, and Neptune • Composed mainly of gaseous and liquid hydrogen and its compounds, these planets lack solid surfaces and may have cores The Outer Planets of molten rock • The dwarf planets Pluto and Eris are exceptions to these rules resembling the ice and rock makeup of the giant planets’ larger moons • The moons of the outer planets form families of miniature solar systems, although individually each moon presents a unique combination of size, structure, and appearance 1 2 Jupiter Jupiter • Jupiter is the largest • Clouds appear to be planet both in diameter particles of water, ice, and and mass: more than10× ammonia compounds Earth’s diameter and • Bright colors of clouds may 300× the mass! come from complex • Dense, richly colored organic molecules or parallel cloud bands compounds of sulfur or cloak the planet phosphorous • Atmosphere is mainly • Jupiter rotates once about H, He, CH , NH , and every 10 hours with this 4 3 fast rotation leading to a H2O 3 significant equatorial bulge 4 Jupiter’s Interior Jupiter’s Interior • Jupiter, with a core temperature of about 30,000 K, emits more energy than it receives – Possibly due to heat left • Jupiter’s average density is 1.3 • Deeper still, liquid hydrogen over from its creation g/cm 3 – indicates an interior compresses into liquid metallic – Planet may still be composed of very light hydrogen, a material scientists elements only recently created in tiny shrinking in size converting gravitational • Interior becomes increasingly high-pressure chambers dense with depth, gas turning • An iron rocky core, a few energy into heat to liquid hydrogen about times bigger than the Earth, 10,000 km down probably resides5 at the center 6 Jupiter’s Atmosphere Jupiter’s Atmosphere • General convection pattern: – Heat within Jupiter carries gas to the top of the atmosphere – High altitude gas radiates into space, • cools and sinks Coriolis effect turns rising and sinking gases into powerful jet streams (about 300 7 km/hr) that are seen as cloud belts 8 Jupiter’s Atmosphere The Great Red Spot • Adjacent belts, with different relative speeds, create vortices of various colors, the largest being the Great Red Spot, which has persisted for over 300 years 9 10 Jupiter’s Magnetic Field Jupiter’s Magnetic Field • Convection in the deep metallic liquid hydrogen • Magnetic field also layer coupled with Jupiter’s rapid rotation traps charged particles creates a powerful far above the planet magnetic field in regions resembling – 20,000× stronger than the Earth’s field, it is the the Earth’s Van Allen largest planetary magnetic radiation belts field – Jupiter’s auroral activity • Lightning in clouds and intense radio has been observed emissions are indicative of its magnetic field 11 12 Jupiter’s Ring The Moons of Jupiter • Solar radiation and collisions with charged particles trapped in Jupiter’s magnetic field exert a friction on the ring dust that will eventually cause the dust to drift into the atmosphere • Jupiter currently has 63 natural • To maintain the ring, satellites or moons Jupiter has a thin ring made new dust must be of tiny particles of rock • Number changes frequently as more dust and held in orbit by provided – possibly from Jupiter’s gravity collision fragments are discovered ejected from the Jovian • Four innermost moons are called the moons Galilean Moons 13 14 The Moons of Jupiter Io • Except for Europa, all are larger than the Moon • Gravitational tidal forces • Ganymede is the largest Moon in the Solar System, induced from Jupiter and and has an intrinsic magnetic field! Europa keeps Io’s interior hot • Formed in a process similar to the formation of the Solar System – the density of these satellites • Volcanic plumes and lava decreases with distance from Jupiter flows are the result 15 16 Europa Liquid Water Ocean on Europa? • Very few craters indicate interior heating by Jupiter and some radioactive decay • Surface looks like a cracked egg indicating a “flow” similar to glaciers on Earth • Heating may be enough to keep a layer of water melted below the crust 17 18 Ganymede and Callisto Other Observations • Look like Moon with • Callisto may have • Galilean average densities • Rest of Jupiter’s moons are grayish brown color and subsurface liquid water indicate their interiors to much smaller than the covered with craters be composed mainly of Galilean satellites and they • Ganymede is less cratered are cratered rocky material • However, their surfaces than Callisto indicating • Outermost moons have orbits are mostly ice – whitish maria-type formations • Differentiation may have that have high inclinations craters a very good although tectonic allowed iron to sink to suggesting that they are indication of this movement cannot be core captured asteroids ruled out 19 20 Saturn Interior of Saturn • Saturn is the second largest planet, 10× Earth’s diameter and 95 × Earth’s mass • Its average density of 0.7 g/cm 3 is less than than of water • Low density, like Jupiter, suggests a Saturn looks different from Jupiter – • Saturn radiates more energy conversion of gravitational composition mostly temperature is low enough for than it receives, but unlike energy from falling helium ammonia gas to freeze into cloud of hydrogen and its particles that veil its atmosphere’s Jupiter, this energy probably droplets as they condense in compounds deeper layers comes from the Saturn’s interior 21 22 The Rings of Saturn Ring Structure • Rings are wide but thin – Main band extends from • Rings not solid, but about 30,000 km above its made of a swarm of atmosphere to about twice individual bodies Saturn’s radius (136,000 km) – Sizes range from – Faint rings can be seen centimeters to meters closer to Saturn as well as – Composition mainly farther away water, ice, and – Thickness of rings: a few carbon compounds hundred meters and is not uniform – Visible A, B and C rings, across rings from outside in 23 24 Ring Structure The Roche Limit • Any object held together solely by gravity will break • Large gaps due to apart by tidal forces if it gets too close to the planet. resonances with • Distance of breakup is called the Roche limit and is Saturn’s moons 2.44 planetary radii if object and planet have the same located beyond the density rings • All planetary rings lie near their planet’s Roche limit • Narrow gaps due to • Existence of side-by-side ringlets of different complex interaction compositions indicates rings supplied by varied between ring particles comets and asteroids and tiny moons in the • Objects bonded together chemically will survive rings Roche limit 25 26 The Roche Limit Saturn’s Moons • Saturn has several large moons and many more smaller ones • Like Jupiter, most of the moons form a mini-solar system, but unlike Jupiter, Saturn’s moons are of similar densities indicating that they were not heated by Saturn as they formed • Saturn’s moons have a smaller density than those of Jupiter indicating interiors must be mostly ice • Most moons are inundated with craters, many of which are surrounded by white markings of shattered ice • The moons also have several surface features that have yet to be explained 27 28 Saturn’s Moons Titan • Saturn’s largest moon • Larger than Mercury • Mostly nitrogen atmosphere • Solid surface with liquid oceans of methane • The Huygens Probe landed on the surface 29 30 Images from Titan’s Surface Uranus • Uranus was not discovered until 1781 by Sir William Herschel • While small relative to Jupiter/Saturn, Uranus is 4× larger in diameter than Earth and has 15× the mass • At 19 AU, Uranus is difficult to study from Earth, but even close up images from Voyager reveal a rather featureless object 31 32 Atmosphere of Uranus Interior of Uranus • With a density of 1.2 g/cm 3 and smaller size, Uranus must contain proportionally fewer light elements than Jupiter/Saturn • Density is too low for it to contain much rock or iron • Uranus’s interior probably contains water, methane, and ammonia • Size of equatorial bulge supports the idea that the interior is mostly water and other hydrogen-rich molecules and that it may have a rock/iron core • Atmosphere is rich in • Methane gas and ice are • hydrogen and methane responsible for the blue It is currently not known if the core formed first and attracted lighter gases that condensed on it, or the core color of Uranus’s formed by differentiation after the planet formed. atmosphere 33 34 Interior of Uranus Uranus’s Odd Tilt • Uranus’s spin axis is tipped so • Uranus may have been struck that it nearly lies in its orbital during its formation and plane splashed out material to form • The orbits of Uranus’s moons the moons, or gravitational 35 are similarly tilted forces may have36 tipped it Rings of Uranus Moons of Uranus • Uranus is encircled by a • Uranus has 5 large set of narrow rings moons and several small composed of meter-sized ones that form a regular objects system • These objects are very • Moons probably dark, implying they are composed of ice and rich in carbon particles or rock and many show organic-like materials heavy cratering • The extremely narrow • Miranda is very unique rings may be held in place in that it appears to have by shepherding satellites been torn apart and 37 reassembled 38 Neptune Interior of Neptune • Neptune is similar in size to • Neptune’s interior is Uranus probably similar to • Deep blue world with cloud bands and vortex structures Uranus’s – mostly – the Great “Dark” Spot ordinary water being, at one time, the most surrounded by a thin prominent feature atmosphere rich in • Neptune was discovered from predictions made by hydrogen and its John C.