The Jupiter System. Rings, Moons, and Pluto. The Orbits of Jupiter s s Moons. The Saturn System. Jupiter has 16 satellites

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1 Rings, Moons, and Pluto All the giant planets have moons that orbit them like planets in a miniature solar system There are 60 satellites known in the outer solar system Several of the moons are larger than Pluto and have atmospheres of their own Pluto resembles these satellites more that it resembles the other 8 planets All the giant planets have rings Rings consist of billions of small particles or moonlets The Jupiter System Jupiter has 16 satellites 4 large moons discovered by Galileo Callisto, Ganymede, Europa, Io Europa and Io are about the size of the Moon Ganymede and Callisto are bigger than Mercury Remaining 12 moons are much smaller The inner 4 orbit inside the orbit of Io Of the remaining 8 small moons 4 have highly inclined orbits 4 have retrograde orbits May be captured objects 1 2 The Orbits of Jupiter s s Moons Simulation The Saturn System Saturn has 19 known satellites The largest is Titan, which is almost as big as Juptier s Ganymede Titan is the only moon with a substantial atmosphere (more later) 6 other moons have regular orbits Several moons orbit near the rings 2 distant, irregular moons, one retrograde The rings of Saturn are spectacular Broad, flat, few gaps Rings are a collection of icy fragments with sizes ranging from a ping pong ball to a basketball 3 4

2 The Orbits of Saturn s s Moons Simulation The Uranus System The ring and satellite system of Uranus is tilted 98 degrees just like the planet itself 11 rings Only discovered in 1977 Narrow ribbons with broad gaps Composed of icy, dark material 18 moons The 5 largest satellites are similar to the 6 regular satellites of Saturn The 13 smaller moons are very dark Simulation 5 6 The Neptune System Neptune has 8 satellites 6 regular satellites close to the planet and two irregular satellites farther out Triton is a relatively large moon in a retrograde orbit Triton has an atmosphere and active volcanoes Neptune has rings Narrow and faint Composed of dark, icy material Simulation Name Moon Callisto Ganymede Europa Io Titan The Largest Satellites Diameter (km) Mass (Moon=1) Density (g/cm 3 ) Reflectivity (%)

3 Callisto, an Ancient and Primitive World Callisto orbits Jupiter at a distance of 2 million km and circles Jupiter in 17 days Callisto has the same rotational period as orbital period like the Moon The surface temperature of Callisto is -140 degrees centigrade Callisto is about the same size as Mercury but with only 1/3 the mass of Mercury Callisto has much less rocky materiel than Mercury Callisto is undifferentiated Callisto was frozen solid before differentiation was completed The Ice of Callisto The surface of Callisto is composed of water ice This ice is much colder than ice on Earth and does not flow like Earth s glaciers The surface of Callisto is covered with impact craters There is no geological activity on Callisto Generally the craters on Callisto resemble the crater on the Moon When one looks in detail at the crater, they show erosion Results from sublimation of water leaving behind a dusty material 9 10 Portrait of Callisto Callisto was a nymph, beloved of Zeus and hated by Hera. Hera changed her into a bear and Zeus then placed her in the sky as the constellation Ursa Major. 11 Ganymede, the Largest Satellite About 1/4 of the surface of Ganymede is cratered The remaining surface area was formed more recently Sparse, fresh craters About 1 billion years old Younger than the lunar maria or martial plains Ganymede is differentiated Has a rocky core about the size of the Moon Has a magnetic field The young surface is the result of tectonic and volcanic forces Some features formed when the crust cracked and water flooded craters Mountain ranges were formed from compression of the crust Impact craters were split and pulled apart May have been caused by tidal forces from Jupiter 12

4 Portrait of Ganymede Ganymede was a Trojan boy of great beauty whom Zeus carried away to be cup bearer to the gods. Europa, the Satellite with an Ocean Europa is similar to the Moon Predominantly rock Heat from the forming Jupiter combined with continuous heating from tidal forces evaporated most of the water on Europa However, Europa retains an ice-covered surface There are very few impact craters on Europa Surface is younger than a few million years Europa is better able to erase impact craters than Earth Cracks and long ridges on the icy surface suggest that there is liquid water under the surface Heat is derived from tidal forces May be sufficient for primitive life Portrait of Europa Europa was a Phoenician princess abducted to Crete by Zeus, who had assumed the form of a white bull, and by him the mother of Minos. Io, a Volcanic Satellite Io, a Volcanic Satellite Io is the inner most satellite of Jupiter Similar to the Moon in size and density Io has the highest level of volcanism in the solar system Volcanic eruptions are visible on the surface of Io The lava is similar to lava on Earth Sometimes the lava comes in contact with frozen layers of sulfur and sulfur dioxide and produces huge plumes The surface of Io is constantly changing Tidal heating keeps Io active 15 16

5 Portrait of Io Io was a maiden who was loved by Zeus (Jupiter) and transformed into a heifer in a vain attempt to hide her from the jealous Hera. Titan, a Satellite with an Atmosphere Titan, the largest satellite of Saturn, was discovered in 1655 by the Dutch Astronomer Christian Huygens, the first moon to be found after Galileo saw the four large moons of Jupiter Titan is roughly the same size as Callisto and Ganymede but its composition is unknown Titan has a substantial atmosphere Has a pressure 1.6 times Earth Mostly nitrogen Contains other gases Carbon dioxide, methane, ethane, propane Hydrogen cyanide, cyanogen, cyanoacetylene Active chemistry thought to be the progenitor of life on Earth The Structure of Titan s s Atmosphere Titan has multiple layers of clouds These clouds completely obscure the surface of Titan The surface temperature is about 90 K Methane can exist as solid, liquid, gas at these temperatures Organic compounds are stable in Titan s atmosphere May hold chemical history dating back billions of years Cassini and Huygens will try to find some answers in 2004 Portrait of Titan In Greek mythology the Titans were a family of giants, the children of Uranus and Gaia, who sought to rule the heavens but were overthrown and supplanted by the family of Zeus

6 Triton and its Volcanoes Triton is the largest satellite of Neptune Triton has a diameter of 2720 km and a density of 2.1 g/cm 3 Suggests 75% rock and 25% water ice The surface of Triton is very cold 35 to 40 K The surface of Triton is made of frozen water, nitrogen, methane, and carbon monoxide Impact craters on Triton are erased by lava flows Melted ices The southern pole of Triton is covered with a polar ice cap In summer, the ice cap is heated and geysers are created 10 km high Discovery of Pluto Pluto was discovered through a careful systematic search rather than having a good prediction of where to look as was the case for Neptune Percival Lowell spent the last 10 years of his life (he died in 1916) searching unsuccessfully for the ninth planet In 1930, Clyde Tombaugh found the ninth planet after an exhaustive search using photographic plates and the blinker method Tombaugh worked at the Lowell Observatory Used a camera donated by Lowell s brother Recent measurements show there are no more planets IRAS, Voyager, Pioneer Portrait of Triton In Greek mythology, Triton is a god of the sea, the son of Poseidon (Neptune); usually portrayed as having the head and trunk of a man and the tail of a fish. Pluto s s Motion and Satellite Pluto s orbit has a large inclination to the ecliptic (17 ) Pluto s orbit takes it closer to the Sun than Neptune but there is no chance of collision because of the angle of inclination Pluto requires years to circle the Sun Pluto s rotational axis is tilted 90 degrees similar to Uranus Pluto has a moon, Charon Retrograde orbit in the ecliptic (not along Pluto s equator) About half the size of Pluto Orbital period and rotational period are the same as Pluto s rotational period When Pluto is close to the Sun, it s atmosphere gets thicker 22 24

7 The Origin of Pluto Pluto is different from the other planets Pluto s orbit and composition is very different from the other outer planets Pluto resembles the moons rather than the planets The presence of Charon is puzzling Some astronomers speculate that the strange orbits of Pluto, Charon, Nereid, and Triton are the result of violent collisions during the early history of the outer solar system Planetary Rings All four of the giant planets have rings The rings are made of billions of individual fragments each orbiting the planet There are two formation possibilities Breakup The tidal force of the large planet destroyed existing moons Prevention The tidal forces of the large planet prevented material from coalescing into moons 25 Portrait of Pluto and Charon In Roman mythology, Pluto (Greek: Hades) is the god of the underworld. Charon is named for the mythological figure who ferried the dead across the River Styx into Hades (the underworld). Photo taken by the Hubble Space Telescope The Rings of the Giant Planets

8 The Rings of Saturn The rings of Saturn are very broad and extraordinarily thin 70,000 km wide 20 m thick Ring particles are composed of water ice with sizes ranging from sand to house-size boulders Saturn has three main rings, A, B, C Saturn has narrow rings also that resemble those of Uranus and Neptune 29 Portrait of Saturn and its Rings Photo of Saturn and its rings taken by Voyager 2 In Roman mythology, Saturn is the god of agriculture. The associated Greek god, Cronus, was the son of Uranus and Gaia and the father of Zeus (Jupiter). Rhea Dione 30 The Rings of Uranus and Neptune The rings of Uranus are narrow and black making them almost invisible from Earth The 9 main rings were discovered by watching a star pass behind Uranus Two more rings were discovered by Voyager in 1986 The outermost ring is the Epsilon Ring Contains more mass than the other rings combined Rings are made of black material May be carbon or some hydrocarbon Similar to its ten smaller inner moons Satellite Ring Interactions Gravitational resonances with small inner moons cause structure in rings and may be responsible for the existence of the rings The narrow F ring of Saturn shows strands with bends and kinks Must be under the influence of two shepherd moons, Pandora and Prometheus Narrow gaps in Saturn s rings are associated with small moons that clear lanes in the ring material 31 32