17 Moons Giant Planets

Slide1 : Moons of the Giant Planets Neptune and Triton


Slide3 : This composite image features classic portraits of members of one of the Solar System's most prominent families - Jupiter and its four large Galilean moons. Starting from the top the moons are Io, Europa, Ganymede, and Callisto. Galilean Moons (First seen by Galileo in 1610)


Slide4 : In order from Jupiter they are: Io, a brightly-colored volcanic body; Europa, an ice-covered world; Ganymede, a rock and ice body with some old cratered areas and some younger terrains; and Callisto, an old, cratered body resembling Earth’s Moon. Galilean Moons


Slide5 : Io, Europa, Callisto, and Ganymede, clockwise from upper left. All except Callisto have metallic (iron/nickel) cores, shown in grey, surrounded by rock in brown. The rock shells in Europa and Ganymede are surrounded by liquid water (blue) and ice (white). Callisto is shown as partially differentiated mixture of ice and rock.


Slide6 : Densities Io 3.5 g/cc Europa 3.0 g/cc Ganymede 1.9 g/cc Callisto 1.8 g/cc Young Jupiter was probably very hot causing the inner Moons to be light element depleted, whereas the outer Moons retained more volatile material such as water ice.


Slide7 : Orbits of the Galilean Moons


Slide8 : Io Jupiter’s third largest; it is the innermost of the Galilean moons. Orbit: 422,000 km from Jupiter Io is slightly larger than Earth's Moon. Diameter: 3630 km Io may be somewhat similar in bulk composition to the terrestrial planets, primarily composed of molten silicate rock. Recent data from Galileo indicates that Io has a core of iron (perhaps mixed with iron sulfide) with a radius of at least 900 km.


Slide9 : Io Earth’s Moon


Slide10 : Io is hot! Io is probably the most volcanically active bodies in the solar system. Heat source for volcanism is tidal energy created by gravitational interactions with Jupiter. Heat Flow Io >2.5 Watts/m2 Earth 0.06 Watts/m2 Geothermal 1.7 Watts/m2 Moon 0.02 Watts/m2


Slide11 : Io Volcanism Io is covered with active volcanoes and lava flows. Early interpretation of Voyager images suggested lava flows of sulfur. Problem: sulfur is too weak to support tall volcanic structures. More recent, earth-based infrared telescopic observations indicated very high temperatures. Galilleo probe confirmed volcanic areas with temperatures from 400-1500°C. Consistent with silicate lavas similar to terrestrial planets. Pele Loki


Slide12 : Io Volcanism Io’s volcanism is characterized by calderas, lava lakes, lava flows, and plumes. Over 120 large calderas have been identified. The more we look, the more we find.


Slide13 : Europa Its surface is among the brightest in the solar system, a consequence of sunlight reflecting off a relatively young icy crust. Its surface is also among the smoothest, lacking the heavily cratered appearance characteristic of Callisto and Ganymede. Lines and cracks dominate Europa’s exterior. Europa may be internally active, and its crust may have, or had in the past, liquid water which can harbor life. About forty years ago, astronomer Gerard Kuiper and others showed that Europa's crust was composed of water and ice.


Slide14 : Europa's radius is 1565 km, a bit smaller than our Moon's radius (1738 km). Europa has a metallic (iron, nickel?) core. The core is surrounded by a rock shell (shown in brown). The rock layer of Europa is in turn surrounded by a shell of water in ice or liquid form. Europa’s Interior


Slide16 : Europa’s Surface This picture covers an area about 238 kilometers (150 miles) wide by 225 kilometers (140 miles).


Slide17 : Europa’s Surface 35 by 50 kilometers (20 by 30 miles) Ice rafts


Slide18 : Europa’s Surface Triple bands observed by Voyager were first thought to be formed by tectonic processes, however Galileo images, such the one here, suggest cryo-volcanism along linear fractures with a continuous line of geysers.


Slide20 : The 26-km Pwyll crater has a floor that is the same elevation as surrounding terrain suggesting that it filled immediately with slushy material. Europa’s Craters


Slide21 : Europa’s Craters The impact was followed by the formation of the reddish lines superposed on the crater. The red color designates areas that are probably a dirty water ice mixture. The fine blue-green lines crossing the region from west to east appear to be ridges which formed after the crater. 140- kilometer (86-mile) wide impact crater from a mountain-sized asteroid or comet


Slide22 : Early Solar System or in 7 billion years with Red Giant Sun?


Slide23 : The Europa Orbiter will use a radar sounder to study Europa's icy surface and attempt to determine the thickness of the ice and whether liquid water exists below the ice. Other instruments to study the surface and interior would include an imaging device with multiple filters to map the surface at a resolution of 100 meters and a laser altimeter to measure the topography and characterize the tidal response of the surface. Europa Orbiter From JPL webpage: “2002 April - The Europa Orbiter mission was eliminated from the Administration's FY2003 Budget proposal to Congress. Project activities specific to Europa Orbiter are to be phased out over the remainder of FY2002.”


Slide24 : Jupiter Icy Moons Orbiter (JIMO) Congress cut funding for JIMO in FY2006 -- CANCELLED


Slide25 : Cryobot deploys submarine rover


Slide27 : Ganymede Ganymede is the largest moon in the solar system. It is larger in diameter than Mercury but only about half its mass. Ganymede is much larger than Pluto. Ganymede is most likely composed of a rocky core with a water/ice mantle and a crust of rock and ice. Its low density of 1.94 gm/cm3, indicates that the core takes up about 50% of the satellite's diameter. Ganymede's mantle is most likely composed of ice and silicates, and its crust is probably a thick layer of water ice.


Slide28 : Ganymede has had a complex geological history. It has mountains, valleys, craters and lava flows. Ganymede is mottled by both light and dark regions. It is heavily cratered especially in the dark regions implying ancient origin. The bright regions show a different kind of terrain - one which is grooved with ridges and troughs. These features form complex patterns and have a vertical relief of a few hundred meters and run for thousands of kilometers. The grooved features were apparently formed more recently than the dark cratered area perhaps by tension from global tectonic processes. Ganymede


Slide29 : Ganymede’s “Grooved” Terrain


Slide30 : Callisto Callisto is the second largest moon of Jupiter, the third largest in the solar system, and is about the same size as Mercury. It orbits just beyond Jupiter's main radiation belt. Callisto is the most heavily cratered satellite in the solar system. Its crust is very ancient and dates back 4 billion years, just shortly after the solar system was formed. Callisto has the lowest density (1.86 gm/cm3) of the Galilean satellites. From recent observations made by the Galileo spacecraft, Callisto appears to be composed of a crust about 200 kilometers (124 miles) thick. Beneath the crust is a possible salty ocean more than 10 kilometers (6 miles) thick. Beneath the ocean, is possibly a mixture of rock and ice, with rock increasing downward.


Slide31 : Callisto lacks large mountains. This is probably due to the icy nature of its surface. Impact craters and associated concentric rings are about the only features to be found on Callisto. The largest craters have been erased by the flow of the icy crust over geologic time. Two enormous concentric ring, impact basins are found on Callisto. The largest impact basin is Valhalla (lower left). It has a bright central region that is 600 kilometers in diameter, and its rings extend to 3000 kilometers in diameter. The second impact basin is Asgard. It measures about 1600 kilometers in diameter. Callisto


Slide32 : Titan (Saturn’s largest moon) It has a planet-like atmosphere which is more dense than those of Mercury, Earth, Mars and Pluto. The atmospheric pressure near the surface is about 1.6 bars, 60 percent greater than Earth's. Titan's atmosphere is predominantly made up of nitrogen with other hydrocarbon elements which give Titan its orange hue. These hydrocarbon rich elements are the building blocks for amino acids necessary for the formation of life. It is believed that Titan's environment may be similar to that of the Earth's before life began putting oxygen into the atmosphere.


Slide33 : Titan is the largest moon of Saturn and the second largest moon in the solar system after Jupiter's moon Ganymede, and it is larger by diameter than the smallest planet, Mercury (although only half as massive). Titan's diameter is roughly 50% larger than Earth's moon and it is 80% more massive. Titan was the first known moon of Saturn, discovered in 1655 by the Dutch astronomer Christiaan Huygens Titan - Earth comparison


Slide34 : Along the rim of the lens the following inscriptions can be read: Admovere oculis distantia sidera nostris ("They brought the distant stars closer to our eyes"). The second text is a verse from the Roman poet Ovid and part of the anagram: Admovere oculis distantia sidera nostris vvvvvvv ccc rr h n b q x that Christiaan Huygens sent to some of his scholar friends in the summer of 1655. Huygens did not name the satellite he discovered. He referred to it as Luna Saturni (Saturn's moon). When more moons around Saturn were discovered by other astronomers he simply referred to it as 'my moon', others usually referred to it as 'Huygens' moon'. Christiaan Huygens 1629-1695 The name Titan was proposed in 1847 by the English astronomer John Frederick William Herschel, who supplied mythological names for all the Saturnian moons that were then known, but Herschel's names did not become popular until the end of the 19th century.


Slide35 : Cassini/Huygens is a ESA/NASA mission to the Saturnian System. The spacecraft consists of the NASA Saturn Orbiter and the detachable ESA Huygens Probe designed to explore the atmosphere of Titan, Saturn largest moon.


Slide36 : Huygens Probe landing on Titan (January 2005)


Slide37 : A scale replica of the probe, 1.3 meters across. Huygens probe


Slide38 : This side-by-side image shows a Cassini radar image (on the left) of what is the largest body of liquid ever found on Titan's north pole, compared to Lake Superior (on the right). This close-up is part of a larger image (see PIA09182) and offers strong evidence for seas on Titan. These seas are most likely liquid methane and ethane. Titan Sea This feature on Titan is at least 100,000 square kilometers (39,000 square miles), which is greater in extent than Lake Superior (82,000 square kilometers or 32,000 square miles), which is Earth's largest surface area lake.


Slide39 : Image of Titan taken during Huygens’ descent, showing hills and topographical features that resemble a shoreline and drainage channels. Shoreline?


Slide40 : After landing, Huygens photographed a dark plain covered in small rocks and pebbles, which are composed of water ice. The two rocks just below the middle of the image on the left are smaller than they may appear: the left-hand one is 15 centimeters (6 inches) across, and the one in the center is 4 centimeters (about 1.5 inches) across, at a distance of about 85 centimeters (about 33 inches) from Huygens.


Slide41 : Origin and Evolution of Titan’s Atmosphere Saturn, being considerably smaller than Jupiter, probably was not as hot during its formation and evolution. Thus Titan retained a significant amount of its volatile inventory and this explains this moon’s dense atmosphere. Early measurements from Earth-based instruments suggested that Titan’s atmosphere was dominated by methane (CH4), however Voyager 1 determined that the dominant gas is molecular nitrogen N2 (82-99%) just as on Earth. Titan has 10 times more N2 than Earth’s atmosphere. Methane is only a few percent of the Titan atmosphere.


Slide42 : The orbit of Titan, highlighted in red among the other large inner moons of Saturn. The outer moons are Iapetus and Hyperion; the inner moons are Rhea, Dione, Tethys, Enceladus and Mimas. Titan is tidally locked in synchronous orbit around Saturn


Slide43 : Titan Atmosphere


Slide44 : This natural color image shows Titan's upper atmosphere -- an active place where methane molecules are being broken apart by solar ultraviolet light and the byproducts combine to form compounds like ethane and acetylene.


Slide45 : The brighter region on the right side and equatorial region is named Xanadu Regio. The images hint at a young surface with, no obvious craters. The dark area at the center left of the image almost looks like a possible hydrocarbon "sea", complete with four large easily-identifiable "islands" and a "shoreline" running northeast to southwest. A mosaic of nine processed images acquired during Cassini's first very close flyby of Saturn's moon Titan on Oct. 26, 2004.


Slide46 : Titan's surface temperature is about 94 K (−179 °C, or −290 °F). At this temperature water ice does not sublimate from solid to gas, so the atmosphere is nearly free of water vapor. The haze in Titan's atmosphere contributes to the moon's anti-greenhouse effect by reflecting sunlight away from the satellite, making its surface significantly colder than its upper atmosphere. The clouds on Titan, probably composed of methane, ethane or other simple organics, are scattered and variable, punctuating the overall haze. The findings of the Huygens probe indicate that Titan's atmosphere periodically rains liquid methane and other organic compounds onto the moon's surface. In October, 2007, observers noted an increase in apparent opacity in the clouds above the equatorial Xanadu region, suggestive of "methane drizzle", though this was not direct evidence for rain. It is possible that areas of Titan's surface may be coated in a layer of tholins, but this has not been confirmed. Titan’s Surface


Slide48 : Titan’s Interior


Slide49 : Titan’s Interior


Slide50 : Triton is the largest moon of Neptune, with a diameter of 2,700 kilometers (1,680 miles). Triton is colder than any other measured object in the Solar System with a surface temperature of -235° C (-391° F). It has an extremely thin atmosphere. Nitrogen ice particles might form thin clouds a few kilometers above the surface. The atmospheric pressure at Triton's surface is about 15 microbars, 0.000015 times the sea-level surface pressure on Earth. Triton (Neptune’s largest moon) Near-IR spectroscopy shows that Triton's high-albedo surface is covered largely with N2 ice, with <1% CH4 and a small amount of CO dissolved in the N2. Solid CO2 and H2O are also seen in the spectrum.


Slide51 : Triton is the only large satellite in the solar system to circle a planet in a retrograde direction -- in a direction opposite to the rotation of the planet. It has a density of about 2.066 grams per cubic centimeter. This means Triton contains more rock in its interior than the icy satellites of Saturn and Uranus do. The relatively high density and the retrograde orbit has led some scientists to suggest that Triton may have been captured by Neptune as it traveled through space several billion years ago. If that is the case, tidal heating could have melted Triton in its originally eccentric orbit, and the satellite might even have been liquid for as long as one billion years after its capture by Neptune. Triton


Slide52 : Pluto Pluto was discovered in 1930 and remains the only planet that has not been visited by a spacecraft. Pluto is usually farther from the Sun than any of the nine planets; however, due to the eccentricity of its orbit, it is closer than Neptune for 20 years out of its 249 year orbit. Pluto crossed Neptune's orbit January 21, 1979, made its closest approach September 5, 1989, and remained within the orbit of Neptune until February 11, 1999. This will not occur again until September 2226. Surface of the Pluto is resolved in these NASA Hubble Space Telescope pictures, taken with the European Space Agency's (ESA) Faint Object Camera (FOC) aboard Hubble.


Slide53 : Pluto is about two-thirds the diameter of Earth’s Moon. Pluto's average density: 1.8-2.1 g/cc 50% to 75% rock mixed with ices Charon's average density: 1.2-1.3 g/cc (less rock) The differences in density suggest that Pluto and Charon formed independently. Pluto and Charon imaged by the Hubble Space Telescope Pluto and Charon


Slide54 : Pluto and Neptune Orbits No Collision Possible!


Slide55 : Pluto is mostly brownish-green. The above picture captures the true colors of Pluto as well as the highest surface resolution so far recovered. The above map was created by tracking brightness changes from Earth of Pluto during times when it was being partially eclipsed by its moon Charon. Pluto


Slide56 : Pluto – Earth Comparison


Slide57 : Possible structure of Pluto. 1. Frozen methane 2. Water ice 3. Silicate and water ice Pluto Interior


Slide59 : Pluto's icy surface is 98% nitrogen (N2). Methane (CH4) and traces of carbon monoxide (CO) and water (H2O) are also present, but no CO2. Charon has a surface covered with H2O ice, other ices and refractory materials may also exist. The solid methane indicates that Pluto is colder than 70 Kelvin. Pluto's temperature varies widely during the course of its orbit since Pluto can be as close to the sun as 30 AU and as far away as 50 AU. Surface Composition


Slide60 : Pluto has three known natural satellites: Charon, first identified in 1978 by astronomer James Christy; and two smaller moons, Nix and Hydra, both discovered in 2005.


Slide61 : Artist's concept of the surface of Hydra. Pluto with Charon (right) and Nix (bright dot on left).


Slide62 : Pluto-Kuiper Belt Mission Launched Jan. 19, 2006 arrival at Pluto July 2015 There is a thin atmosphere that freezes and falls to the surface as the planet moves away from the Sun. The Pluto-Kuiper Belt Mission will allow scientists to study the planet before its atmosphere freezes. aka New Horizons Mission


Slide64 : New Horizons: Mission Objectives Map surface composition of Pluto and Charon Characterize geology and morphology ("the look") of Pluto and Charon Characterize the neutral atmosphere of Pluto and its escape rate Search for an atmosphere around Charon Map surface temperatures on Pluto and Charon Search for rings and additional satellites around Pluto PLUS... conduct similar investigations of one or more Kuiper Belt Objects


Slide66 : Plot of all known Kuiper belt objects, set against the four outer planets. Gerard Peter Kuiper 1905-1973 Kuiper Belt Mauna Kea, first Kuiper Belt Object in 1992


Slide68 : Objects in resonance are plotted in red (Neptune trojans 1:1, plutinos 2:3, twotinos 1:2,…). Confirmed plutinos are in dark red. Classical objects are plotted in blue. Scattered disk objects (not members of the Kuiper Belt) are shown in grey for reference. Distribution of Kuiper Belt Object orbits


Slide69 : As of 2006, nine stars other than the Sun are known to be circled by Kuiper belt-like structures. They appear to fall into two categories: wide belts, with radii of over 50 AU, and narrow belts (like our own Kuiper belt) with diameters of between 20 and 30 AU and relatively sharp boundaries. Most debris discs around other stars are fairly young, but the two imaged at right, taken by the Hubble Space Telescope in January, 2006, are old enough (roughly 300 million years) to have settled into stable configurations. The left image is a "top view" of a wide belt, and the right image is an "edge view" of a narrow belt.


Slide70 : Oort Cloud Is a postulated spherical cloud of comets situated about 50,000 AU from the Sun. This is approximately 1000 times the distance from the Sun to Pluto or nearly a light year. The outer extent of the Oort cloud places the boundary of our Solar System at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun.


Slide71 : In 1950 the Oort Cloud hypothesis was put forward by Dutch astronomer Jan Hendrik Oort to explain an apparent contradiction: comets are destroyed by several passes through the inner solar system, yet if the comets we observe had really existed for billions of years (since the origin of the solar system), all would have been destroyed by now. According to the hypothesis, the Oort cloud contains trillions of comet nuclei, which are stable because the sun's radiation is very weak at their distance. The cloud provides a continual supply of new comets, replacing those that are destroyed. In order for it to supply the necessary volume of comets, the total mass of comets in the Oort cloud must be many times that of Earth. Jan Hendrik Oort (1900-1992)


Slide73 : Have we found an Oort Cloud object yet? Maybe the Scattered Disk Object “Sedna”.


Slide74 : Sedna (Inuit goddess Sedna, who rules over the seas) Artist's conception of the cold distant Sedna. The sun is a tiny point of light 8 billion miles away from the red planetoid. A hypothesized tiny moon appears nearby. 'extended scattered disc object'


Slide75 : Sedna is the most distant solar system object ever discovered. It is twice as far from the sun as any other solar system object and three times farther than Pluto or Neptune. Standing on the surface of Sedna, you could block the entire sun with the head of a pin held at arm's length.


Slide77 : Stellar Perturbations Stars in the disk of the Milky Way share a common motion around the center of the galaxy but also move relative to each other. At the outer edge of the Oort Cloud, the attraction to the sun is weak and passing stars have a big effect. Comets leave the Oort Cloud because they are perturbed by passing stars. Some of the comets fall into the inner solar system and come under the gravitational control of the planets. Other Perturbations The gravity of the Milky Way disk itself disturbs the orbits of comets in the Oort Cloud, with an effect comparable in size to that of passing stars. The sun may (on very rare occasions) pass through a Giant Molecular Cloud, and this may disturb the Oort Cloud causing a shower of comets to rain on the inner planetary system. Some people have conjectured that the sun has a companion star which could disturb the Oort cloud once per orbit. If so, periodic comet showers might result.


Slide78 : Nemesis is a hypothetical red dwarf or brown dwarf star, orbiting the Sun at a distance of about 50,000 to 100,000 AU, somewhat beyond the Oort cloud. The existence of this star was postulated in an attempt to explain an inferred periodicity in the rate of biological extinction in the geological record.


Slide79 : In 1999, U.K. and U.S. astronomers independently reported finding evidence that one or more large planets or brown dwarfs gravitationally bound to our Sun, may be perturbing the orbits of two different groups of long-period comets at the outer reaches of the Oort Cloud into the inner Solar System with the assistance of galactic tidal forces. The hypothesized object appears to have a mass smaller than one controversial definition for brown dwarfs specifying a minimum mass of at least 13 Jupiters The hypothesized object appears to have a mass smaller than one controversial definition for brown dwarfs specifying a minimum mass of at least 13 Jupiters