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The Solar System Part 2 Saturn through the Oort CloudIt suddenly struck me that that tiny pea, pretty and blue, was the Earth. I put up my thumb and shut one eye, and my thumb blotted out the planet Earth. I didn't feel like a giant. I felt very, very small.-Neil ArmstrongAs most people know our Solar System, for a long time, was considered the home of nine planets.

Saturn

Second largest planet.1/8th the density of Earth, but 95 times its mass.Core is iron and nickel surrounded by metallic and liquid hydrogen and liquid helium.Ammonia crystals give the atmosphere a yellow color.Magnetic field is slightly weaker than Earths.Ring system has 9 rings and 3 arcs, composed of ice and rock.Has many moons with Titan being the 2nd largest in the Solar system.Photo is from the Cassini probe taken in March of 2004.

Saturn is the sixth planet from the Sun and the second largest planet in the Solar System, after Jupiter. Named after the Roman god Saturn, its astronomical symbol () represents the god's sickle. Saturn is a gas giant with an average radius about nine times that of Earth.[12][13] While only one-eighth the average density of Earth, with its larger volume Saturn is just over 95 times more massive than Earth.[14][15][16]Saturn's interior is probably composed of a core of iron, nickel and rock (silicon and oxygen compounds), surrounded by a deep layer of metallic hydrogen, an intermediate layer of liquid hydrogen and liquid helium and an outer gaseous layer.[17] The planet exhibits a pale yellow hue due to ammonia crystals in its upper atmosphere. Electrical current within the metallic hydrogen layer is thought to give rise to Saturn's planetary magnetic field, which is slightly weaker than Earth's and around one-twentieth the strength of Jupiter's.[18] The outer atmosphere is generally bland and lacking in contrast, although long-lived features can appear. Wind speeds on Saturn can reach 1,800km/h (1,100mph), faster than on Jupiter, but not as fast as those on Neptune.[19]Saturn has a prominent ring system that consists of nine continuous main rings and three discontinuous arcs, composed mostly of ice particles with a smaller amount of rocky debris and dust. Sixty-two[20] known moons orbit the planet; fifty-three are officially named. This does not include the hundreds of "moonlets" within the rings. Titan, Saturn's largest and the Solar System's second largest moon, is larger than the planet Mercury and is the only moon in the Solar System to retain a substantial atmosphere.

3Saturn Characteristics

Takes 29.45 years to orbit the Sun.It takes 10 hours for Saturn to rotate once on its axis.It is the only planet that is less dense than water. (0.69 g/cm3).Together Jupiter and Saturn hold 92% of the Solar systems mass.Core is very hot 11, 7000 C. The planet radiates 2.5 times more energy than it receives from the Sun.The clouds are composed of Hydrogen (96.3%) and Helium (3.25%).Ammonia, acetylene, ethane and methane make up the rest of the atmosphere.The winds are second fastest in the Solar system (1800 km/h)The photo shows a great storm which encircled the planet in 2011.Saturns orbit compared to the other planets.

Hexagonal cloud pattern at north pole 2012

The rings extend from 6,630 km to 120,700 km above the equator.93% water ice 7% amorphous carbon.Particles range in size from dust to rocks 10 m in diameter.Rings may have formed from a destroyed moon or they may be left over from the original material that made the planet.Some material seems to come from the moon Enceladuss ice volcanoes.Some of Saturns moons act as shepherd moons. Their gravity helping to keep the rings in place.RingsSaturn is probably best known for the system of planetary rings that makes it visually unique.[31] The rings extend from 6,630km to 120,700km above Saturn's equator, average approximately 20meters in thickness and are composed of 93% water ice with traces of tholin impurities and 7% amorphous carbon.[71] The particles that make up the rings range in size from specks of dust up to 10m.[72] While the other gas giants also have ring systems, Saturn's is the largest and most visible. There are two main hypotheses regarding the origin of the rings. One hypothesis is that the rings are remnants of a destroyed moon of Saturn. The second hypothesis is that the rings are left over from the original nebular material from which Saturn formed. Some ice in the central rings comes from the moon Enceladus's ice volcanoes.[73] In the past, astronomers believed the rings formed alongside the planet when it formed billions of years ago.[74] Instead, the age of these planetary rings is probably some hundreds of millions of years.[75]Beyond the main rings at a distance of 12 million km from the planet is the sparse Phoebe ring, which is tilted at an angle of 27 to the other rings and, like Phoebe, orbits in retrograde fashion.[76] Some of the moons of Saturn, including Pan and Prometheus, act as shepherd moons to confine the rings and prevent them from spreading out.[77] Pan and Atlas cause weak, linear density waves in Saturn's rings that have yielded more reliable calculations of their masses.[78]

7Voyager 1 view of spokes on the Rings

It was expected that collisions between ring particles would tend to make the rings uniform, but Voyager I found changing structures in the radial direction that are termed "spokes". Some of this structure is shown in the adjacent animation. Presently, it is thought that gravitational forces alone cannot account for the spoke structure. Hence, it is possible that some sort of electrostatic repulsion between ring particles may play a role.8Ring Diagram

The rings have gaps caused, in part by Saturns many moons.Some gaps are cleared out areas by moonlets like Pan.Some gaps are maintained by the gravitational effects of shepherd moons.Mimas maintains the Cassini division.The rings possess their own Oxygen atmosphere.It seems that some of the ice comes from the ice volcanoes of Enceladus.While the largest gaps in the rings, such as the Cassini Division and Encke Gap, can be seen from Earth, both Voyager spacecraft discovered that the rings have an intricate structure of thousands of thin gaps and ringlets. This structure is thought to arise, in several different ways, from the gravitational pull of Saturn's many moons. Some gaps are cleared out by the passage of tiny moonlets such as Pan,[17] many more of which may yet be discovered, and some ringlets seem to be maintained by the gravitational effects of small shepherd satellites (similar to Prometheus and Pandora's maintenance of the F ring).[citation needed] Other gaps arise from resonances between the orbital period of particles in the gap and that of a more massive moon further out; Mimas maintains the Cassini division in this manner.[18] Still more structure in the rings consists of spiral waves raised by the inner moons' periodic gravitational perturbations at less disruptive resonances.[citation needed]Cassini space probe view of the unilluminated side of Saturn's rings (May 9, 2007).Data from the Cassini space probe indicate that the rings of Saturn possess their own atmosphere, independent of that of the planet itself. The atmosphere is composed of molecular oxygen gas (O2) produced when ultraviolet light from the Sun interacts with water ice in the rings. Chemical reactions between water molecule fragments and further ultraviolet stimulation create and eject, among other things, O2. According to models of this atmosphere, H2 is also present. The O2 and H2 atmospheres are so sparse that if the entire atmosphere were somehow condensed onto the rings, it would be about one atom thick.[19] The rings also have a similarly sparse OH (hydroxide) atmosphere. Like the O2, this atmosphere is produced by the disintegration of water molecules, though in this case the disintegration is done by energetic ions that bombard water molecules ejected by Saturn's moon Enceladus. This atmosphere, despite being extremely sparse, was detected from Earth by the Hubble Space Telescope

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There are at least 62 moons.The largest is Titan.Many of the moons are very small and some are not named.Some play a strong role in the ring system of this planet.This photo is a montage of pictures taken by the Voyager 1 spacecraft in November 1980. This view shows Dione in the forefront, Saturn rising behind, Tethys and Mimas fading in the distance to the right, Enceladus and Rhea off Saturn's rings to the left, and Titan in its distant orbit at the top.

MoonsSaturn has at least 62 moons, 53 of which have formal names.[79] Titan, the largest, comprises more than 90% of the mass in orbit around Saturn, including the rings.[80] Saturn's second largest moon, Rhea, may have a tenuous ring system of its own,[81] along with a tenuous atmosphere.[82][83][84][85] Many of the other moons are very small: 34 are less than 10km in diameter and another 14 less than 50km.[86] Traditionally, most of Saturn's moons have been named after Titans of Greek mythology. Titan is the only satellite in the Solar System with a major atmosphere[87][88] in which a complex organic chemistry occurs. It is the only satellite with hydrocarbon lakes.[89][90]Saturn's moon Enceladus has often been regarded as a potential base for microbial life.[91][92][93][94] Evidence of this life includes the satellite's salt-rich particles having an "ocean-like" composition that indicates most of Enceladus's expelled ice comes from the evaporation of liquid salt water

10

Its low density means it is mostly made up water ice.It has a very thin atmosphere of oxygen and carbon dioxide.There may be a small ring system orbiting this moon.This picture, taken by the Cassini probe in 2008, shows the ice cliffs and carters common on this moon. Rhea

6th largest moon of Saturn.Cryovolcanoes at the south pole shoot large jets of water ice particles into space.Some of this water falls back onto the moon as snow, some adds to Saturns rings and some reaches the planet itself.This water near the surface may allow Enceladus to support life.This Cassini picture from 2005 shows the cryovolcanoes in the southern hemisphere.EnceladusEnceladus seems to have liquid water under its icy surface. Cryovolcanoes at the south pole shoot large jets of water ice particles into space. Some of this water falls back onto the moon as "snow", some of it adds to Saturn's rings, and some of it reaches Saturn. The whole of Saturn's E ring is believed to have been made from these ice particles. Because of the apparent water at or near the surface, Enceladus may be one of the best places for humans to look for extraterrestrial life. By contrast, the water thought to be on Jupiter's moon Europa is locked under a very thick layer of surface ice12

Enceladus is the sixth-largest of the moons of Saturn.[12] It was discovered in 1789 by William Herschel.[13]Enceladus seems to have liquid water under its icy surface. Cryovolcanoes at the south pole shoot large jets of water ice particles into space. Some of this water falls back onto the moon as "snow", some of it adds to Saturn's rings, and some of it reaches Saturn. The whole of Saturn's E ring is believed to have been made from these ice particles. Because of the apparent water at or near the surface, Enceladus may be one of the best places for humans to look for extraterrestrial life. By contrast, the water thought to be on Jupiter's moon Europa is locked under a very thick layer of surface ice.

13

The mosaic of fractures, folds and ridges in the surface of Enceladus, captured by Nasa's Cassini spacecraft. Photograph: Nasa/JPL/Space Science InstituteEnceladus is 310 miles in diameter.14

This is the largest moon of Saturn and the 2nd largest moon in the Solar System.It is the only one with a dense atmosphere.It is the only other object, other than the Earth, with stable bodies of surface liquid.Titan is primarily composed of water ice and rocks. The surface liquid was discovered to by hydrocarbons.The atmosphere is primarily composed of nitrogen with methane, ethane and organic smog.It has wind, rain, and surface features like rivers, lakes, dunes and seas.TitanTitan (or Saturn VI) is the largest moon of Saturn. It is the only natural satellite known to have a dense atmosphere,[8] and the only object other than Earth for which clear evidence of stable bodies of surface liquid has been found.[9]Titan is the sixth ellipsoidal moon from Saturn. Frequently described as a planet-like moon, Titan has a diameter roughly 50% larger than Earth's moon and is 80% more massive. It is the second-largest moon in the Solar System, after Jupiter's moon Ganymede, and is larger by volume than the smallest planet, Mercury, although only about 41% as massive.

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The Cassini probe arrived at Saturn in 2004.The huygens part of this space probe detached from Cassini and soft-landed on the moon Titan in 2005.This was the first probe to land on a body outside of the inner solar system.Because of the heat loss from the probe it is suspected that Huygens landed in mud.This picture is part of a panorama that shows the surface of Titan as huygens was descending through the clouds.The lake is most likely composed of hydrocarbons. (gasoline)

Cassini-HuygensOn Jan. 14, 2005, the European Space Agency's Huygens probe will descend to the surface of Saturn's largest moon. Get ready for two of the strangest hours in the history of space exploration.Two hours. That's how long it will take the European Space Agency's Huygens probe to parachute to the surface of Titan on January 14th. Descending through thick orange clouds, Huygens will taste Titan's atmosphere, measure its wind and rain, listen for alien sounds and, when the clouds part, start taking pictures.CassiniHuygens is a Flagship-class NASA-ESA-ASI robotic spacecraft sent to the Saturn system.[3] It has studied the planet and its many natural satellites since arriving there in 2004, also observing Jupiter, the Heliosphere, and testing the theory of relativity. Launched in 1997 after nearly two decades of gestation, it includes a Saturn orbiter and an atmospheric probe/lander for the moon Titan called Huygens, which entered and landed on Titan in 2005. Cassini is the fourth space probe to visit Saturn and the first to enter orbit, and its mission is ongoing as of 2013.It launched on October 15, 1997 on a Titan IVB/Centaur and entered into orbit around Saturn on July 1, 2004, after an interplanetary voyage which included flybys of Earth, Venus, and Jupiter. On December 25, 2004, Huygens separated from the orbiter at approximately 02:00 UTC. It reached Saturn's moon Titan on January 14, 2005, when it entered Titan's atmosphere and descended to the surface. It successfully returned data to Earth, using the orbiter as a relay. This was the first landing ever accomplished in the outer Solar System.

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Many of the Rocks in this picture are water ice.There is a mineral/organic dirt or mud that the Huygens landed on.The atmosphere is colored with a hydrocarbon like smog.

Cassini radar image of Titan surface

This radar image, obtained by Cassini's radar instrument during a near-polar flyby on Feb. 22, 2007, shows a big island smack in the middle of one of the larger lakes imaged on Saturn's moon Titan. This image offers further evidence that the largest lakes are at the highest latitudes. The island is about 90 kilometers (62 miles) by 150 kilometers (93 miles) across, about the size of Kodiak Island in Alaska or the Big Island of Hawaii. The island may actually be a peninsula connected by a bridge to a larger stretch of land. As you go farther down the image, several very small lakes begin to appear, which may be controlled by local topography. This image was taken in synthetic aperture mode at 700 meter (2,300 feet) resolution. North is toward the left. The image is centered at about 79 north degrees north and 310 degrees west.

18Mimas

Surface area a bit less than Spain.Density = 1.15 g/cm3, so moslty water ice.Giant impact crater Herschel (81 miles in diameter) nearly split Mimas in two.The central peak in Mimas rises nearly 4 miles about the floor of the crater.

The surface area of Mimas is slightly less than the land area of Spain. The low density of Mimas, 1.15 g/cm, indicates that it is composed mostly of water ice with only a small amount of rock. Due to the tidal forces acting on it, the moon is not perfectly spherical; its longest axis is about 10% longer than the shortest. The ellipsoid shape of Mimas is especially noticeable in recent images from the Cassini probe.Mimas's most distinctive feature is a giant impact crater 130 kilometres (81mi) across, named Herschel after the moon's discoverer. Herschel's diameter is almost a third of the moon's own diameter; its walls are approximately 5 kilometres (3.1mi) high, parts of its floor measure 10 kilometres (6.2mi) deep, and its central peak rises 6 kilometres (3.7mi) above the crater floor. If there were a crater of an equivalent scale on Earth it would be over 4,000 kilometres (2,500mi) in diameter, wider than Australia. The impact that made this crater must have nearly shattered Mimas: fractures can be seen on the opposite side of Mimas that may have been created by shock waves from the impact travelling through the moon's body

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This raw, unprocessed image of Mimas was taken by Cassini on Feb. 13, 2010. The image was taken in visible light with the Cassini spacecraft narrow-angle camera on Feb. 13, 2010. The view was obtained at a distance of approximately 17,000 kilometers (11,000 miles) from Mimas. Image scale is 100 meters (329 feet) per pixel.

20Uranus has the 4th largest mass in the Solar System.Uranus and Neptune are considered ice giants.It has the coldest atmosphere in the Solar System (-2240 C)Uranus has a ring system, a magnetosphere and numerous moons.Its axial tilt is 970, so its poles are in line with the plane of the Solar SysteOrbital period is 84 years and a day is 17 hours. Its rotation is clockwise (retrograde).Wind speeds can reach 560 mph.This diagram shows the position of two new moons discovered by Hubble and the Ring structure.

UranusUranus is the seventh planet from the Sun. It has the third-largest planetary radius and fourth-largest planetary mass in the Solar System. Uranus is similar in composition to Neptune, and both are of different chemical composition than the larger gas giants Jupiter and Saturn. For this reason, astronomers sometimes place them in a separate category called "ice giants". Uranus's atmosphere, although similar to Jupiter's and Saturn's in its primary composition of hydrogen and helium, contains more "ices" such as water, ammonia, and methane, along with traces of hydrocarbons.[12] It is the coldest planetary atmosphere in the Solar System, with a minimum temperature of 49K (224C). It has a complex, layered cloud structure, with water thought to make up the lowest clouds, and methane thought to make up the uppermost layer of clouds.[12] In contrast, the interior of Uranus is mainly composed of ices and rock.[11]Like the other gas giants, Uranus has a ring system, a magnetosphere, and numerous moons. The Uranian system has a unique configuration among the planets because its axis of rotation is tilted sideways, nearly into the plane of its revolution about the Sun. Its north and south poles therefore lie where most other planets have their equators.[16] In 1986, images from Voyager 2 showed Uranus as a virtually featureless planet in visible light without the cloud bands or storms associated with the other giants.[16] Terrestrial observers have seen signs of seasonal change and increased weather activity in recent years as Uranus approached its equinox. The wind speeds on Uranus can reach 250 meters per second (900km/h, 560mph)

21Voyager approaching UranusUranus orbit compared with the other planets

A 1998 false-colour near-infrared image of Uranus showing cloud bands, rings, and moons obtained by the Hubble Space Telescope's NICMOS camera.

Uranus with cloud bands

Uranus in 2005. Rings, southern collar and a bright cloud in the northern hemisphere are visible. (HST ACS image).Uranus magnetic field. It does not originate from the center.It does not line up well with the geographic north and south poles.

Miranda

These photos are from Voyager 2, 1986Miranda is the most geologically active moon.It is 288 miles in diameter.The surface is mostly water ice with some silicate rock in the interior.It is suspected that its unusual terrain was the result of gravitational interactions with another moon umbriel.It is the closest large moon to Uranus.So far the only close-up images of Miranda are from the Voyager 2 probe, which made observations of the moon during its Uranus flyby in January 1986. During the flyby the southern hemisphere of the moon was pointed towards the Sun so only that part was studied. Miranda shows more evidence of past geologic activity than any of the other Uranian satellites.Miranda's surface may be mostly water ice, with the low-density body also probably containing silicate rock and organic compounds in its interior.Miranda's surface has patchwork regions of broken terrain indicating intense geological activity in the moon's past, and is criss-crossed by huge canyons. Large 'racetrack'-like grooved structures, called coronae, may have formed via extensional processes at the tops of diapirs, or upwellings of warm ice.[7][8] The ridges probably represent extensional tilt blocks. The canyons probably represent graben formed by extensional faulting. Other features may be due to cryovolcanic eruptions of icy magma. The diapirs may have changed the density distribution within the moon, which could have caused Miranda to reorient itself,[9] similar to a process believed to have occurred at Saturn's geologically active moon Enceladus.

30Titania

Titania is the largest of the moons of Uranus and the eighth largest moon in the Solar System at a diameter of 981mi.It consists of equal amounts of rock and ice.Infrared spectroscopy conducted from 2001 to 2005 revealed the presence of water ice as well as frozen carbon dioxide on the surface of Titania. This is a Voyager 2 image of Titania's southern hemisphere taken on January 24, 1986.The Voyager 2 flyby is the only time the Uranian system has been photographed.Titania consists of approximately equal amounts of ice and rock, and is probably differentiated into a rocky core and an icy mantle. A layer of liquid water may be present at the coremantle boundary. The surface of Titania, which is relatively dark and slightly red in color, appears to have been shaped by both impacts and endogenic processes. It is covered with numerous impact craters reaching up to 326 kilometres (203mi) in diameter, but is less heavily cratered than the surface of Uranus's outermost moon, Oberon.31Neptune

8th and farthest planet from the Sun.4th largest by diameter and 3rd largest by mass.The only pictures come from Voyager 2 in 1989.Orbital period is 165 years.Rotates once about every 18 hours.13 known moons.Very active, stormy atmosphere with the Great Dark Spot.Winds speed up to 1,300 mph.Has a faint fragmented ring system. Neptune is the eighth and farthest planet from the Sun in the Solar System. It is the fourth-largest planet by diameter and the third-largest by mass. Neptune is 17 times the mass of Earth and is somewhat more massive than its near-twin Uranus, which is 15 times the mass of Earth but not as dense.[12] On average, Neptune orbits the Sun at a distance of 30.1 AU, approximately 30 times the EarthSun distance.Neptune has been visited by only one spacecraft, Voyager 2, which flew by the planet on 25 August 1989.In contrast to the hazy, relatively featureless atmosphere of Uranus, Neptune's atmosphere is notable for its active and visible weather patterns. For example, at the time of the 1989 Voyager 2 flyby, the planet's southern hemisphere possessed a Great Dark Spot comparable to the Great Red Spot on Jupiter. These weather patterns are driven by the strongest sustained winds of any planet in the Solar System, with recorded wind speeds as high as 2,100 kilometres per hour (1,300mph).[17] Because of its great distance from the Sun, Neptune's outer atmosphere is one of the coldest places in the Solar System, with temperatures at its cloud tops approaching 218C (55K). Temperatures at the planet's centre are approximately 5,400 K (5,000C).[18][19] Neptune has a faint and fragmented ring system (labeled 'arcs'), which may have been detected during the 1960s but was only indisputably confirmed in 1989 by Voyager 32

5 principal rings.First imaged by Voyager 2 in 1989.System is similar to Uranus ring system.

The rings of Neptune consist primarily of five principal rings and were first discovered (as "arcs") in 1984 in Chile by Patrice Bouchet, Reinhold Hfner and Jean Manfroid at La Silla Observatory (ESO) during an observing program proposed by Andr Brahic and Bruno Sicardy from Paris-Meudon Observatory, and at Cerro Tololo Interamerican Observatory by F. Vilas and L.-R. Elicer for a program led by Williams Hubbard [1] [2]. They were eventually imaged in 1989 by the Voyager 2 spacecraft.[3] At their densest, they are comparable to the less dense portions of Saturn's main rings such as the C ring and the Cassini Division, but much of Neptune's ring system is quite tenuous, faint and dusty, more closely resembling the rings of Jupiter34Neptune orbit compared with the other planets.

Triton

1,688 miles in diameter. 7th largest moon.Retrograde orbit and icy composition cause people to believe it is a captured Kuiper Belt object.Surface is frozen nitrogen and water ice.It has a rocky core.This picture is from Voyager 2 1989.Triton has the coldest surface known anywhere in the Solar System, -3910F. Most of Triton's nitrogen is condensed as frost, making it the only satellite in the Solar System known to have a surface made mainly of nitrogen iceNeptune has thirteen known moons, by far the largest of which is Triton, discovered by William Lassell on October 10, 1846, just 17 days after the discovery of Neptune itself. Over a century passed before the discovery of the second natural satellite, called Nereid. Neptune's moons are named for minor water deities in Greek mythology.Unique among moons of planetary mass, Triton is an irregular satellite, as its orbit is retrograde to Neptune's rotation and inclined relative to the planet's equator. The next-largest irregular satellite in the Solar System, Saturn's moon Phoebe, is only 0.03% Triton's mass. Triton is massive enough to have achieved hydrostatic equilibrium and to retain a thin atmosphere capable of forming clouds and hazes. Both its atmosphere and its surface are composed mainly of nitrogen with small amounts of methane and carbon monoxide. Triton's surface appears relatively young, and was probably modified by internally driven processes within the last few million years. The temperature at its surface is about 38K (235.2C).Inward of Triton are six regular satellites, all of which have prograde orbits in planes that lie close to Neptune's equatorial plane. Some of these orbit among Neptune's rings. The largest of them is Proteus.Neptune also has six outer irregular satellites, including Nereid, whose orbits are much farther from Neptune, have high inclinations, and are mixed between prograde and retrograde. The two outermost ones, Psamathe and Neso, have the largest orbits of any natural satellites discovered in the Solar System to date.Triton is the largest moon of the planet Neptune, discovered on October 10, 1846, by English astronomer William Lassell. It is the only large moon in the Solar System with a retrograde orbit, which is an orbit in the opposite direction to its planet's rotation. At 2,700km in diameter, it is the seventh-largest moon in the Solar System. Because of its retrograde orbit and composition similar to Pluto's, Triton is thought to have been captured from the Kuiper belt.[10] Triton has a surface of mostly frozen nitrogen, a mostly water ice crust,[11] an icy mantle and a substantial core of rock and metal.

36Pluto2nd most massive dwarf planet after Eris.One of several comet-like bodies in the Kuiper Belt.Pluto is composed primarily of rock and ice. It is approximately one-sixth the mass of the Earth's Moon and one-third its volume.Pluto has five known moons, the largest being Charon, discovered in 1978.In 2015 the New Horizons will give us the first close look at Pluto and its moons. 246 years to orbit the Sun.It rotates once every 6.39 days.It is half ice and half rock.The picture is a Hubble view of Pluto and its rotation.

Pluto, formal designation 134340 Pluto, is the second-most-massive known dwarf planet in the Solar System (after Eris) and the tenth-most-massive body observed directly orbiting the Sun.[h] Originally classified as the ninth planet from the Sun, Pluto was recategorized as a dwarf planet and plutoid owing to the discovery that it is only one of several large bodies within the Kuiper belt.37Charon

Discovered in 1978.Diameter is 750 miles.Seems to be mostly nitrogen and methane ice.This is a Hubble view of Pluto and Charon taken in 1990.Some feel that Charon formed from an impact.

Charon was discovered by U.S. Naval Observatory astronomer James Christy, using the 1.55-meter telescope at NOFS,[8] and was formally announced to the world via the International Astronomical Union on July 7, 1978.[9] On June 22, 1978, he had been examining highly magnified images of Pluto on photographic plates taken at the 61-inch Flagstaff telescope two of months prior. Christy noticed that a slight elongation appeared periodically. Later, the bulge was confirmed on plates dating back to April 29, 1965.Subsequent observations of Pluto determined that the bulge was due to a smaller accompanying body. The periodicity of the bulge corresponded to Pluto's rotation period, which was previously known from Pluto's light curve. This indicated a synchronous orbit, which strongly suggested that the bulge effect was real and not spurious.All doubts were erased when Pluto and Charon entered a five-year period of mutual eclipses and transits between 1985 and 1990. This occurs when the PlutoCharon orbital plane is edge-on as seen from Earth, which only happens at two intervals in Pluto's 248-year orbital period. It was fortuitous that one of these intervals happened to occur so soon after Charon's discovery.Charon's diameter is about 1,207 kilometres (750mi), just over half that of Pluto, with a surface area of 4,580,000 square kilometres (1,770,000sqmi). Unlike Pluto, which is covered with nitrogen and methane ices, the Charonian surface appears to be dominated by less volatile water ice, and also appears to have no atmosphere. In 2007, observations by the Gemini Observatory of patches of ammonia hydrates and water crystals on the surface of Charon suggested the presence of active cryo-geysers.[10][11] (See also Cryovolcano.) Mutual eclipses of Pluto and Charon in the 1980s allowed astronomers to take spectra of Pluto and then the combined spectrum of the pair. By subtracting Pluto's spectrum from the total, astronomers were able to spectroscopically determine the surface composition of Charon.The two conflicting theories about Charon's internal structureCharon's volume and mass allow calculation of its density from which it can be determined that Charon is largely an icy body and contains less rock by proportion than its partner Pluto. This supports the idea that Charon was created by a giant impact into Pluto's icy mantle.

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Charon's Pluto-facing hemisphere (determined from brightness variations during PlutoCharon occultations), rendered by Celestia. Based on mapping work done by39Pluto and its moons

A pair of small moons orbiting Pluto, which were discovered by NASAs Hubble Space Telescope, have been named Nix and Hydra. Discovered in 2005, the two moons are roughly 5,000 times fainter than Pluto and are about two to three times farther from Pluto than its large moon, Charon, which was discovered in 1978. 40

This image, taken by NASA's Hubble Space Telescope, shows five moons orbiting the distant, icy dwarf planet Pluto. The newly discovered small moon, designated P5, is the innermost of the moons found by Hubble over the past seven years. The diagram shows that P5 is in a 58,000-mile-diameter circular orbit around Pluto that is assumed to be co-planar with the other satellites in the system. Though Charon (discovered in 1978) is an even closer moon to Pluto, some astronomers consider the Pluto-Charon pair a "double planet" because Charon's mass is 12 percent of Pluto's mass (by comparison, our Moon is .01 percent Earth's mass). This image was taken with Hubble's Wide Field Camera 3 on July 7. 41Kuiper Belt

Similar to the Asteroid belt only much larger. (30 to 50 AU).Consists mainly of small icy bodies.It is home to at least three dwarf planets: Pluto, Haumea and Makemake.It is felt that some of the outer planets moons (Triton, phoebe) are captured Kuiper bodies.First discovered in 1990, now over 1,000 KBO,s over 62 miles in diameter are known.Not the source of periodic comets as was originally thought.In the diagram objects in the belt are green, scattered are orange and are called centaurs.

The Kuiper belt /kjupr/ or /kapr/, sometimes called the EdgeworthKuiper belt, is a region of the Solar System beyond the planets, extending from the orbit of Neptune (at 30 AU) to approximately 50 AU from the Sun.[1] It is similar to the asteroid belt, but it is far larger20 times as wide and 20 to 200 times as massive.[2][3] Like the asteroid belt, it consists mainly of small bodies, or remnants from the Solar System's formation. While most asteroids are composed primarily of rock and metal, most Kuiper belt objects are composed largely of frozen volatiles (termed "ices"), such as methane, ammonia and water. The classical belt is home to at least three dwarf planets: Pluto, Haumea, and Makemake. Some of the Solar System's moons, such as Neptune's Triton and Saturn's Phoebe, are also believed to have originated in the region.Since the belt was discovered in 1992,[6] the number of known Kuiper belt objects (KBOs) has increased to over a thousand, and more than 100,000 KBOs over 100km (62mi) in diameter are believed to exist.[7] The Kuiper belt was initially thought to be the main repository for periodic comets, those with orbits lasting less than 200 years. However, studies since the mid-1990s have shown that the classical belt is dynamically stable, and that comets' true place of origin is the scattered disc, a dynamically active zone created by the outward motion of Neptune 4.5billion years ago;[8] scattered disc objects such as Eris have extremely eccentric orbits that take them as far as 100 AU from the Sun.Known objects in the Kuiper belt, derived from data from the Minor Planet Center. Objects in the main belt are colored green, while scattered objects are colored orange. The four outer planets are blue. Neptune's few known trojans are yellow, while Jupiter's are pink. The scattered objects between Jupiter's orbit and the Kuiper belt are known as centaurs.42

Quaoar ("Kwawar") is a rocky trans-Neptunian object in the Kuiper belt with one known moon.Has a diameter of 731 miles.Orbits the Sun every 286 years. The picture is an artists impression of the dwarf planet and its moon Weywot.QuaoarQuaoar was the first trans-Neptunian object to be measured directly from Hubble Space Telescope (HST) images, using a new, sophisticated method (see Browns pages for a non-technical description and his paper[18] for details). Given its distance Quaoar is on the limit of the HST resolution (40 milliarcseconds) and its image is consequently "smeared" on a few adjacent pixels. By comparing carefully this image with the images of stars in the background and using a sophisticated model of HST optics (point spread function (PSF)), Brown and Trujillo were able to find the best-fit disk size which would give a similar blurred image. This method was recently applied by the same authors to measure the size of Eris.45

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Most massive dwarf planet. 2,326 km (1,454 mi.) in diameter.Discovered 2005Three times farther away than Pluto.Eris was discovered in January 2005 by a Palomar Observatory-based team. It is a trans-Neptunian object (TNO). It is a member of a high-eccentricity population known as the scattered disc. It has one known moon, Dysnomia.

ErisEris, minor-planet designation 136199 Eris, is the most massive known dwarf planet[c] in the Solar System and the ninth most massive body known to orbit the Sun directly.[c][d] It is estimated to be 2326 (12)km in diameter,[9] and 27% more massive than Pluto, or about 0.27% of the Earth's mass.[10][16]Eris was discovered in January 2005 by a Palomar Observatory-based team led by Mike Brown, and its identity was verified later that year. It is a trans-Neptunian object (TNO) and a member of a high-eccentricity population known as the scattered disc. It has one known moon, Dysnomia. As of 2011, its distance from the Sun is 96.6AU,[13] roughly three times that of Pluto. With the exception of some comets, Eris and Dysnomia are currently the most distant known natural objects in the Solar System.[2][e]Because Eris appeared to be larger than Pluto, its discoverers[19] and NASA initially described it as the Solar System's tenth planet. This, along with the prospect of other similarly sized objects being discovered in the future, motivated the International Astronomical Union (IAU) to define the term planet for the first time. Under the IAU definition approved on August24, 2006, Eris is a "dwarf planet", along with objects such as Pluto, Ceres, Haumea and Makemake.This discovery forced people to precisely define a planet.According to the IAU (International Astronomical Union); a planet is a body that orbits the Sun, is massive enough for its own gravity to make it round, and has "cleared its neighbourhood" of smaller objects around its orbit. This discovery forced people to precisely define a planet.According to the IAU (International Astronomical Union); a planet is a body that orbits the Sun, is massive enough for its own gravity to make it round, and has "cleared its neighbourhood" of smaller objects around its orbit.

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The scattered disk contains far distant (30 to 100 AU) objects with extremely elliptical orbits.These objects have been affected by the gravity of Neptune and their orbits have been changed. It is felt that most periodic comets and some of the moons of Neptune, Uranus and Saturn came from these bodies.This is a Hubble photo of Eris and its moon Dysnomia.Scattered Disk

Discovered in 2004 at Palomar.Egg shape is caused by rapid rotation.Haumea is a plutoid, a dwarf planet beyond Neptune.It orbits the Sun every 283 Earth years.It is about 720 miles long.The surface is most likely composed of water ice.The two moons are named Rudolph and Blitzen

HaumeaHaumea, minor-planet designation 136108 Haumea, is a dwarf planet[19] located beyond Neptune's orbit. Just one-third the mass of Pluto,[20] it was discovered in 2004 by a team headed by Mike Brown of Caltech at the Palomar Observatory in the United States and, in 2005, by a team headed by J. L. Ortiz at the Sierra Nevada Observatory in Spain, though the latter claim has been contested and neither is official. On September 17, 2008, it was recognized as a dwarf planet by the International Astronomical Union (IAU) and named after Haumea, the Hawaiian goddess of childbirth.Haumea's extreme elongation makes it unique among known dwarf planets. Although its shape has not been directly observed, calculations from its light curve suggest it is an ellipsoid, with its major axis twice as long as its minor. Nonetheless, its gravity is believed sufficient for it to have relaxed into hydrostatic equilibrium, making it a dwarf planet. This elongation, along with its unusually rapid rotation, high density, and high albedo (from a surface of crystalline water ice), are thought to be the results of a giant collision, which left Haumea the largest member of a collisional family that includes several large trans-Neptunian objects (TNOs) and its two known moons.Haumea is a plutoid,[21] a dwarf planet residing beyond Neptune's orbit. Its status as a dwarf planet means it is presumed to be massive enough to have been rounded by its own gravity but not to have cleared its neighbourhood of similar objects.

50MakemakeDiameter about 2/3 that of Pluto.Covered with methane, ethane and nitrogen ices.Very reflective and bright for its size.Not discovered until 2005 because of its severe inclination from the solar system disk.With its stable orbit it is now considered the largest body yet found in the Kuiper Belt.

Makemake, minor-planet designation 136472Makemake, is a dwarf planet and perhaps the largest Kuiper belt object (KBO) in the classical population,[nb 5] with a diameter that is about 2/3 the size of Pluto.[9][17] Makemake has no known satellites, which makes it unique among the largest KBOs and means that its mass can only be estimated. Its extremely low average temperature, about 30K (243.2C), means its surface is covered with methane, ethane, and possibly nitrogen ices.[14]Initially known as 2005 FY9 and later given the minor-planet number 136472, it was discovered on March 31, 2005, by a team led by Michael Brown, and announced on July 29, 2005. Makemake was recognized as a dwarf planet by the International Astronomical Union (IAU) in July 2008.[18][17][19][20] Its name derives from Makemake in the mythology of the Rapanui people of Easter Island.

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Named after Jan Oort.Lies from 2,000 to as far as 50,000 AU out.Inner section is doughnut shaped (2,000 to 20,000 AU).Outer section is spherical and weakly bound to the Sun.Defines the boundary of the Solar System.Made up of icy planestismals.It may be the source of some cometsSedna and three other bodies are the only known Oort cloud members.The Oort cloud /rt/[1] (named after Jan Oort), or pikOort cloud,[2] is a hypothesized spherical cloud of predominantly icy planetesimals that may lie roughly 50,000 AU, or nearly a light-year, from the Sun.[3] This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun. The Kuiper belt and the scattered disc, the other two reservoirs of trans-Neptunian objects, are less than one thousandth of the Oort cloud's distance. The outer limit of the Oort cloud defines the cosmographical boundary of the Solar System and the region of the Sun's gravitational dominance52Thought to be a remnant of the early solar system.Thought to be the source of long period comets like Hale-Bopp.The Scattered disc is thought to be the origin of short period comets.

The Oort cloud is thought to be a remnant of the original protoplanetary disc that formed around the Sun approximately 4.6billion years ago.[3] The most widely accepted hypothesis is that the Oort cloud's objects initially coalesced much closer to the Sun as part of the same process that formed the planets and asteroids, but that gravitational interaction with young gas giant planets such as Jupiter ejected the objects into extremely long elliptic or parabolic orbits.[3][26] Recent research has been cited by NASA hypothesizing that a large number of Oort cloud objects are the product of an exchange of materials between the Sun and its sibling stars as they formed and drifted apart, and it is suggested that many possibly the majority of Oort cloud objects were not formed in close proximity to the Sun.[5] Simulations of the evolution of the Oort cloud from the beginnings of the Solar System to the present suggest that the cloud's mass peaked around 800million years after formation, as the pace of accretion and collision slowed and depletion began to overtake supply53

Short-period (200 years or less) comets come from the Kuiper belt or the scattered disks.This would include comets like Halley.Comet Halley returns every 76 years.This is a photo from its last visit in 1985.

CometsComets are believed to have two separate points of origin in the Solar System. Short-period comets (those with orbits of up to 200years) are generally accepted to have emerged from the Kuiper belt or scattered disc, two linked flat discs of icy debris beyond Neptune's orbit at 30AU and jointly extending out beyond 100AU from the Sun. Long-period comets, such as comet HaleBopp, whose orbits last for thousands of years, are thought to originate in the Oort cloud. The orbits within the Kuiper belt are relatively stable, and so very few comets are believed to originate there. The scattered disc, however, is dynamically active, and is far more likely to be the place of origin for comets.[12] Comets pass from the scattered disc into the realm of the outer planets, becoming what are known as centaurs.[32] These centaurs are then sent farther inward to become the short-period comets.54

Nucleus of Comet Halley seen from space probe Giotto.Every time Halley returns it loses about 6 meters of its surface.This debris forms the Orionids Meteor shower

Here is what a comet nucleus really looks like. For all active comets except Halley, it was only possible to see the surrounding opaque gas cloud called the coma. During Comet Halley's most recent pass through the inner Solar System in 1986, however, spacecraft Giotto was able to go right up to the comet and photograph its nucleus. The above image is a composite of hundreds of these photographs. Although the most famous comet, Halley achieved in 1986 only 1/10th the brightness that Comet Hyakutake did last year, and a similar comparison is likely with next year's pass of Comet Hale-Bopp. Every 76 years Comet Halley comes around again, and each time the nucleus sheds about 6 meters of ice and rock into space. This debris composes Halley's tails and leaves an orbiting trail that, when falling to Earth, are called the Orionids Meteor Shower. 56Note the gas (blue) and dust (white) tails. This picture is from 1997, Will not return until 4385.Its orbit carries it 520 AU from the Sun. Thought to come from the Oort cloud.Was visible for a record 18 months. Was called the great comet of 1997

was perhaps the most widely observed comet of the 20th century and one of the brightest seen for many decades. It was visible to the naked eye for a record 18months57

The Oort cloud is thought to occupy a vast space from somewhere between 2,000 and 5,000 AU (0.03 and 0.08 ly)[12] to as far as 50,000AU (0.79ly)[3] from the Sun. Some estimates place the outer edge at between 100,000 and 200,000 AU (1.58 and 3.16 ly).[12] The region can be subdivided into a spherical outer Oort cloud of 20,00050,000AU (0.320.79ly), and a doughnut-shaped inner Oort cloud of 2,00020,000AU (0.030.32ly). The outer cloud is only weakly bound to the Sun and supplies the long-period (and possibly Halley-type) comets to inside the orbit of Neptune.[3] The inner Oort cloud is also known as the Hills cloud, named after J. G. Hills, who proposed its existence in 1981.[13] Models predict that the inner cloud should have tens or hundreds of times as many cometary nuclei as the outer halo;[13][14][15] it is seen as a possible source of new comets to resupply the relatively tenuous outer cloud as the latter's numbers are gradually depleted. The Hills cloud explains the continued existence of the Oort cloud after billions of years.58

3 times as far away as Neptune.Surface is icy.Orbits the Sun once every 11,400 years.Orbit varies from 76 AU to 937 AU.Considered the first known object of the Oort cloud.Diameter of 625 miles.One of the reddest objects in the sky.

Sedna90377 Sedna is a large trans-Neptunian object, which as of 2012 was about three times as far from the Sun as Neptune. Spectroscopy has revealed that Sedna's surface composition is similar to that of some other trans-Neptunian objects, being largely a mixture of water, methane and nitrogen ices with tholins. Its surface is one of the reddest in the Solar System. It is believed to be a dwarf planet by several astronomers,[11][12][13][14][15] and is large enough to be considered one under the 2006 draft proposal of the IAU,[16] though the IAU has not formally recognized it as such.[17][18]For most of its orbit it is even farther from the Sun than at present, with its aphelion estimated at 937 astronomical units[3] (31 times Neptune's distance), making it one of the most distant known objects in the Solar System other than long-period comets.[c][d] Sedna's exceptionally long and elongated orbit, taking approximately 11,400 years to complete, and distant point of closest approach to the Sun, at 76AU, have led to much speculation as to its origin. The Minor Planet Center currently places Sedna in the scattered disc, a group of objects sent into highly elongated orbits by the gravitational influence of Neptune. However, this classification has been contested, as Sedna never comes close enough to Neptune to have been scattered by it, leading some astronomers to conclude that it is in fact the first known member of the inner Oort cloud.

59How the solar system looks from Sedna. As seen from Sedna, the Sun would form somewhat of an isosceles triangle with Spica to the lower right and Antares to the lower left.

Largest body in Solar System without a name.551 years to orbit the Sun.Currently 86.5 AU from the Sun.Another very red object, possibly due to methane frost.Has no moons.

2007 OR10(225088) 2007 OR10 is a very large trans-Neptunian object. It is the largest body in the Solar System without a name,[8] estimated to be between Haumea and Sedna in size. It appears to be a dwarf planet,[9][10][11] and is easily large enough to be considered one under the 2006 draft proposal of the IAU.2007 OR10 is currently the largest known object in the Solar System without an official name. In 2011 Brown decided he finally had enough information to justify giving it one, because the discovery of water ice and the possibility of methane makes it noteworthy enough to warrant further study.2007 OR10 came to perihelion around 1856.[4] It is currently 86.5 AU from the Sun.[7][16] This makes it the 3rd-farthest known large body in the Solar System, after Eris (97 AU) and Sedna (87 AU).[8] It will be farther from the Sun than Sedna in 2013.[16] 2007 OR10 will be farther than both Sedna and Eris by 2045,[17] and it will reach aphelion (farthest distance from the Sun) in 2130

61Artist impression of 2007 OR10

IAU definition A planet is round, has cleared its orbit of debris and orbits the Sun. This is an artists impression of the view of the Sun from 2007 OR10

According to the vote, a planet is a celestial body that orbits the Sun, has a nearly round shape, and has cleared its orbit of extraneous debris. Another classification was added to the terms used by astronomers: dwarf planet. A dwarf planet is essentially something that looks like a planet but is not a planet. Pluto is now considered a dwarf planet, as is the asteroid Ceres. Along with the aforementioned Eris and Snow White, Haumea, Makemake, Sedna, Quaoar, and Orcus are also likely to be dwarf planets. Plutos moon Charon would also fit if it were not a moon. There are dozens more that await further investigation.63