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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
9
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.
15
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.
16
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
19
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.
38
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
46
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.
48
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.
51
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