Chapter 12 Rings, Moons, and Pluto PDF

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Chapter 12 Rings, Moons, and Pluto...

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Chapter 12: Rings, Moons, and Pluto Rings All four giant planets have rings. ● Saturn: ice particles spread out into several vast, flat rings ● Uranus & Neptune: composed of dark particles confined to a few narrow rings ● Jupiter: composed of dust particles Moons of Jupiter ● 61+ moons and a faint ring ● Galilean satellites ○ "Ganymede" and "Callisto" are larger than Mercury ○ "Io" and "Europe" are about the size of our Moon ● many other Moons may be captured asteroids Callisto is the outermost of the Galilean moons, at a distance of 1.2 million mi. ● it is in synchronous revolution around Jupiter, every 17 days ● the moon has a heavily cratered surface that has seen little change over the last 4.4 billion years ● froze solid before the process of differentiation occurred. It is geologically dead. Ganymede the largest moon in the Solar System ● parts of its surface are very old, like Callisto, but others are relatively young, perhaps a billion years old ● may have a rocky, metallic core ● tidal forces may occasionally heat the interior and cause water to erupt and resurface portions of the moon Europa a predominantly rocky world, with an ice-covered surface that is crisscrossed with cracks and low ridges. ● few craters are evident ● ice appears to be the frozen surface of a great water ocean that has broken up and refrozen many times ● tidal forces may generate enough heat to keep water in the liquid state not too far beneath the surface layer of ice Io is a close twin to our moon, with about the same size and density. ● has active volcanoes on its surface ○ volcanoes emit hot, rocky, lava, sulfur, and sulfur oxide ○ the sulfur and sulfur dioxide recondenses in the cold, and snows down upon Io's surface ● is constantly resurfacing itself Moons of Saturn 19 moons and a massive ring system ● "Titan" is the most significant satellit moon and the only one with a significant atmosphere ● ring material is the size of ping-pong, tennis, and basketballs Titan is about the size of Jupiter's Ganymede, and about half ice/half rock

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it is the only moon to have a substantial atmosphere the atmospheric surface pressure is 1.6 times that of Earth atmosphere is composed mother of methane. N2 and hydrocarbon compounds are also present ● methane composed clouds shroud the surface. It is probably covered with methane ice and perhaps methane oceans. Tethys its icy surface is heavily cratered and contains cracks caused by faults in the ice. ● there is one enormous trench about 65km wide, extending from above the center to the extreme left. It covers 3/4ths of Tethys' circumference. ● the fissure is about the size scientists would predict if Tethys' was once fluid, and its crust hardened before the interior ● the canyon has been named Ithica Chasma Enceladus is one of the innermost moons on Saturn. ● reflects almost 100% of sunlight that strikes it ● the uncratered regions are geologically young, and suggest that Enceladus has experienced a period of relatively recent internal melting ● the rims of several craters near the lower center of the picture have been flooded by the smooth terrain Dione was discovered in 1684. ● is an icy body with a density of 1.43 gm/cm3, which makes it the second densest moon of Saturn (next to Titan) ● probably composed of a rocky core making up 1/3 of the moon's mass, with the rest being water-ice ● its icy surface includes heavily cratered terrain, moderately cratered plains, lightly cratered plains, and wispy material ○ Mimas and Herschel is surprisingly large in comparison to the size of the moon. ■ Herschel is 130km wide, and 1/3 the diameter of Mimas ● it is 10km deep, with a central mountain almost as high as Mt. Everest on Earth ● this central mountain rises 6km above the crater floor ● its impact probably came close to disintegrating the moon Moons of Uranus 26+ moons and 11 dark rings Miranda a moon that may have broken up and then reassembled ● its surface is unlike anything in the Solar System with features that are jumbled together in a haphazard fashion ● consists of huge fault canyons as deep as 20km, terraced layers, and a mixture of old/young surfaces ● may have been shattered as many as 5 times during its evolution ○ after each shattering, the moon would have reassembled from the remains of its former self with portions of the core exposed and portions of the surface buried ● across the ridges and valleys are many faults ○ the largest fault scarp, or cliff, may be 5km (3mi) high, or higher than the walls of

the Grand Canyon on Earth Moons of Neptune 13+ moons Triton is the largest moon of Neptune; has a large satellite in retrograde orbit ● has the coldest temperature of any object unmanned spacecrafts have visited, about -35 to 40 degrees above absolute zero. ● is so cold that N2 and CH4 are frozen on its surface ● is 75% rock and 25% ice water The Discovery of Pluto Percival Lowell ● known for promoting the "canals" on Mars, was intrigued by possible irregularities in Neptune's motion ● predicted that "Planet X" was affecting Neptune ● launched a decades-long search for Planet X at his private observatory in Arizona ● hired Clyde Tombaugh. This 24-year old farm boy with a passion for astronomy was hired by Lowell Observatory Flagstaff, Arizona in 1929 ○ his task was to continue the search for Planet X using a wide-field camera ○ in Feb. 1930, he spotted a moving object that turned out to be Pluto ○ Planet X was announced to the world on March 14th, 1930 Recent Discoveries About Pluto (since 1930 - 1976) Size Composition ● NASA's Spitzer Space Telescope measures the heat from Pluto... even at -360o F Atmosphere ● Nitrogen (N2), Methane (CH4), Carbon Monoxide (CO), and various hydrocarbons Moons ● two more moons are found in 2005 by Hal Weaver, Alan Stern, and the Pluto Companion Search Team ● "Nix" and "Hydra" are about 60-120km in diameter ○ orbits Pluto in 24.9 and 32.2 days What's it like being on Pluto? ● cold, beyond cold ○ temp. is about 55K (absolute) = -218o C or -360o F ○ at this temp., N2 is solid ice ● dimly lit by a distant Sun and appears the same size as Jupiter appears from Earth ○ the light from the Sun is 1,000 times faster than it is on Earth ● profoundly lonely ○ none of the other planets can be seen with the naked eye ○ no comets come to visit

More specifically... ● the surface is glassy ice, with reddish brown stains and no rocks anywhere ● toxic hydrocarbons slowly drift downward from high in the atmosphere ● has a thin atmosphere with a foggy layer ● Charon is always in the sky, or never in the sky. 31/2 degrees across and 7x's the size of our moon ● other little moons come and go (Nix, Hydra). They're fairly bright. ● each year is 248 Earth-years long ● the distant Sun moves ever so slowly among the stars (everyone was born under the same astrological sign based off age) ● Nix and Hydra are visible to the naked eye ● the stars wobble slightly ● each day is 77 hours long ● geysers may erupt from the surface, just as on Triton A new wave of discoveries beyond Pluto began in 1992, enabled by new technology... ● about 1,000 of these objects have been found in the last 14 years ● they're cold, like Pluto, and some are similar in composition ● they've been called the "ice dwarfs," in contrast to the gas giant planets and the terrestrial planets ○ three of the four largest ice dwarfs have moons.... ■ is this a coincidence? About 10% of all Kuiper Belt objects have moons The Discovery of Charon (1978) ● was discovered by accident in July, 1987 by Jim Christy and Bob Harrington of the US Naval Observatory ● is in synchronous orbit about 19,600km from Pluto (17 Rpl) and tidally spin-spin-orbit locked with a 6.4 day period ● is grey and covered in H2O(s) and perhaps ammonium hydrates ● radius is 50% of Pluto's ○ mass is about 10% ○ the mutual barycenter is between the two the IAU speaks... ● a planet is a celestial body that is 1. in orbit around the sun 2. has sufficient mass to be spherical 3. has cleared the neighborhood around its orbit ---> this includes Mercury through Neptune = 8 classical planets ● a "dwarf planet" is a celestial body that is 1. in orbit around the Sun 2. has sufficient mass to be spherical 3. has not cleared its neighborhood 4. is not a satellite

---> this includes Pluto, Eris, Sedna, and a few other large Kuiper Belt Objects The "New Horizons" Mission to Pluto ● map the surfaces (craters, ice flows, other geological structures) of Pluto and its moons ● study the atmosphere, search for an atmosphere of the largest moon (Charon) ● study the surface compositions of Pluto and its moons ● continue on into the Kuiper Belt to study one or more Kuiper Belt objects beyond Pluto...