The Outer Planets Introduction v Beyond the orbit

The Outer Planets

Introduction v Beyond the orbit of Mars, the low temperatures of the solar nebula allowed condensing bodies there to capture hydrogen and hydrogen-rich gases v This together with the vast amount of material in the outer Solar System lead to the creation of the four large Jovian planets – Jupiter, Saturn, Uranus, and Neptune v Composed mainly of gaseous and liquid hydrogen and its compounds, these planets lack solid surfaces and may have cores of molten rock v Pluto is an exception to these rules resembling the ice and rock makeup of the giant planets’ larger moons The Outer Planets 2

Jupiter v Jupiter’s appearance and physical properties l Jupiter is the largest planet both in diameter and mass l more than 10 x Earth’s diameter and 300 x the mass Dense, richly colored parallel cloud bands cloak the planet l Atmosphere is mainly H, He, CH 4, NH 3, and H 2 O l Clouds appear to be particles of water, ice, and ammonia compounds l Bright colors of clouds may come from complex organic molecules with composition still unknown l The Outer Planets 3

Jupiter v Jupiter’s interior l Interior becomes increasingly more dense as center is approached with its gaseous upper layers turning to liquid hydrogen about 10, 000 km below the surface l Deeper still, liquid hydrogen compresses into liquid metallic hydrogen, a material scientists only recently created in tiny high-pressure chambers l An iron rocky core, a few times bigger than the Earth, probably resides at the center The Outer Planets 4

Jupiter v Jupiter’s interior (continued) l Jupiter, with a core temperature of about 30, 000 K, emits more energy than it receives Possibly due to heat left over from its creation l Planet may still be shrinking in size converting gravitational energy into heat l v Jupiter’s atmosphere l General convection pattern: Heat within Jupiter carries gas to the top of the atmosphere l High altitude gas radiates into space, cools and sinks l The Outer Planets 5

Jupiter v Jupiter’s ring l Jupiter has a thin ring made of tiny particles of rock dust and held in orbit by Jupiter’s gravity v Jupiter’s moons l Jupiter currently has 63 natural satellites or moons l Most of the moons are too small to be seen from Earth and were discovered by examining pictures taken by the Voyager spacecraft The Outer Planets 6

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Jupiter v Jupiter’s moon (continued) l Galilean satellites Io, Europa, Ganymede, and Callisto Discovered by Galileo l Except for Europa, all are larger than the Moon l Ganymede is the largest Moon in the Solar System l The Outer Planets 8

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Jupiter v Jupiter’s moons (continued) l Other observations Galilean average densities indicate their interiors to be composed mainly of rocky material l Rest of Jupiter’s moons are much smaller than the Galilean satellites and they are cratered l Outermost moons have orbits with high inclinations suggesting that they are captured asteroids l The Outer Planets 10

Saturn v Saturn’s Appearance and Physical Properties Saturn is the second largest planet with a diameter and mass more than 10 x Earth’s diameter and 95 x the mass l It has a low density which suggests a composition mostly of hydrogen and its compounds l Internal structures similar to Jupiter l Saturn’s atmosphere looks different than Jupiter’s because Saturn is cold enough for ammonia gas to freeze into cloud particles that veil its atmosphere’s deeper layers l The Outer Planets 11

Saturn v Saturn’s Rings l Rings are wide but thin Main band extends from about 30, 000 km above its atmosphere to about twice Saturn’s radius (136, 000 km) l Faint rings can be seen closer to Saturn as well as farther away l Thickness of rings: a few hundred meters l l Rings not solid, but made of a swarm of individual bodies Sizes range from centimeters to meters l Composition mainly water, ice, and carbon compounds and is not uniform across rings l The Outer Planets 12

Saturn v Origin of Planetary Rings l Rings once thought to be left over remains from a planet’s formation l Ring lifetime is short, so for rings to persist they must be replenished The Outer Planets 13

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Saturn v Saturn’s Moons l Saturn has several large moons and many more smaller ones l Like Jupiter, most of the moons form a minisolar system, but unlike Jupiter, Saturn’s moons are of similar densities indicating that they were not heated by Saturn as they formed l Saturn’s moons have a smaller density than those of Jupiter indicating interiors must be mostly ice l Most moons are inundated with craters, many of which are surrounded by white markings of shattered ice The Outer Planets 15

Saturn v Saturn’s Moons (continued) l Titan The largest moon, is bigger than Mercury and second to Ganymede in Moon sizes l Distance from Sun allows Titan to have a nitrogen atmosphere l Clouds shroud surface, which is believed to have oceans of methane l Methane rain may fall from clouds l The Outer Planets 16

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Uranus v Introduction l Unknown to the ancients, even though visible to the naked eye, Uranus was not discovered until 1781 by Sir William Herschel l While small relative to Jupiter/Saturn, Uranus is 4 x larger in diameter than Earth and has 15 x the mass l At its far distance, Uranus is difficult to study from Earth, but even close up images from Voyager reveal a rather featureless object v Uranus’s Atmosphere l Atmosphere is rich in hydrogen and methane l Methane gas and ice are responsible for the blue color of Uranus’s atmosphere The Outer Planets 18

Uranus v Uranus’s Interior l Uranus’s interior probably contains water, methane, and ammonia v Uranus’ Rotation l Uranus spins on its side l It is believed that long ago a very large object smashed into this planet. l The crash was so powerful that it completely changed the direction of Uranus' spin The Outer Planets 19

Uranus v Uranus’s Rings and Moons l Rings Encircled by a set of narrow rings composed of meter-sized objects l These objects are very dark, implying they are rich in carbon particles or organic-like materials l l Moons Uranus has 5 large moons and several small ones l Moons probably composed of ice and rock and many show heavy cratering l Miranda is very unique in that it appears to have been torn apart and reassembled l The Outer Planets 20

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Neptune v Introduction l Neptune is the outermost of the Jovian giants and similar in size to Uranus l A deep blue world with cloud bands and vortex structures l Neptune was discovered from predictions made by John C. Adams and Urbain Leverrie, who calculated its orbit based on disturbances in Uranus’s orbit v Neptune’s Structure l Neptune’s interior is probably similar to Uranus’s – mostly ordinary water surrounded by a thin atmosphere rich in hydrogen and its compounds and probably has a rock/iron core The Outer Planets 22

Neptune v Neptune’s Atmosphere l Neptune’s blue, like Uranus, comes from methane in its atmosphere l Neptune has cloud belts l Neptune’s winds are extremely fast reaching speeds of 2200 km/hr and creating visible vortex structures The Outer Planets 23

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Neptune v Neptune’s Rings and Moons l Rings Neptune, like the other giant planets, has rings l They are probably the debris from small satellites or comets that have collided and broken up l The rings are not distributed uniformly around the ring indicating they are relatively new l The Outer Planets 25

Neptune v Neptune’s Rings and Moons (continued) l Moons Neptune has six small moons orbiting close to the planet and two moons farther out l One of the two is Triton l l Triton is large enough and far enough from the others to retain an atmosphere Triton has some craters with dark steaks extending from them – at least one of which originates from a geyser caught in eruption by the passing Voyager II The material in the geyser is thought to be a mixture of nitrogen, ice and carbon compounds heated beneath the surface by sunlight until it expands and bursts to the surface The Outer Planets 26

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Pluto v Survey l Discovered by Clyde Tombaugh in 1930 by scanning millions of star images over the course of a year l Pluto’s large distance and very small size makes it difficult to study, even in the largest telescopes l In 1978, James Christy discovered Charon, Pluto’s moon l The orbiting combination of Pluto and Charon allows an accurate measurement of their masses – Pluto is the least massive planet The Outer Planets 28

Pluto v Survey (continued) l Pluto is 1/5 the diameter of Earth l Charon is relatively large, being about ½ Pluto’s diameter l From these masses and diameters, Pluto is an object of water, ice, and rock l Very little is known of Pluto’s surface l Pluto was once thought to be a moon of Neptune that escaped; now it is thought Neptune captured Pluto, a remnant planetesimal The Outer Planets 29

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