1. The Solar System - Its Origin and Early Development
Sun and eddy

2. Solar System
The Solar System consists of the Sun and the other celestial objects gravitationally bound to it: the eight planets, three dwarf planets and their 165 known moons.
4 terrestrial planets or inner planets
The Asteroid Belt
4 gas giants or outer planets
The Kuiper Belt
The Oort Cloud
Three dwarf planets scattered thru the solar system

3. General Characteristics of the Solar System
Planetary orbits and rotation
Planet and satellite orbits are in a common plane
Nearly all planet and satellite orbital and spin motions are in the same direction
Rotation axes of nearly all planets and satellites are roughly perpendicular to the plane of the ecliptic

4. General Characteristics of the Solar System
Chemical and physical properties of the planets
The terrestrial planets are small, have a high density, and are composed of rock and metallic elements
The Jovian planets are large, have a low density, and are composed of gases and frozen compounds

5. General Characteristics of the Solar System
The three dwarf planets are Pluto, the largest known Kuiper belt object; Ceres, the largest object in the asteroid belt; and Eris, which lies in the scattered disc.

6. Planetary Distances: In order of their distances from the Sun
Mercury AU
Venus AU
Earth AU
Mars AU
Jupiter AU
Saturn AU
Uranus AU
Neptune AU
Pluto (dwarf planet) AU
Light travels through space at 300,000-km/s.
So it takes about 8 minutes for light from the sun to travel 1 AU and reach us.
How long would it take light from the sun to reach Pluto?
39 x 8 = 312 minutes, or 5.2 hours!

7. Mass of the Solar System
Almost all the mass in our solar system is in the sun.
Mass of the Solar System
Sun 99.80%
Jupiter 0.10%
Comets 0.05%
Other 7 planets 0.04%
Total of Sun + Planets + Comets = 99.99%

8. Planets A planet is any body in orbit around the Sun that
has enough mass to form itself into a spherical shape and
has cleared its immediate neighborhood of all smaller objects.
There are eight known planets that meets this qualification: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune.

9. Dwarf Planets
On August 24, 2006 the International Astronomical Union defined the term "planet" for the first time, excluding Pluto and reclassifying it under the new category of dwarf planet along with Eris and Ceres.
Images of the Asteroid Ceres As It Rotates One Quarter

10. Dwarf Planets
A dwarf planet is not required to clear its neighborhood of other celestial bodies. Other objects that may become classified as dwarf planets are Sedna, Orcus, and Quaoar.

12. Small Solar System Bodies
Natural satellites, or moons, are those objects in orbit around planets, dwarf planets and SSSBs, rather than the Sun itself.

13. The Solar System
The eight bodies officially categorized as planets are often further classified in several ways:
Chemical Composition
Size
Position Relative to the Sun
Position Relative to the Earth
By History

14. Chemical Composition
Terrestrial or rocky planets: Mercury, Venus, Earth, and Mars:
The terrestrial planets are composed primarily of rock and metal and have relatively high densities, slow rotation, solid surfaces, no rings and few satellites.
Jovian or gas planets: Jupiter, Saturn, Uranus, and Neptune:
The gas planets are composed primarily of hydrogen and helium and generally have low densities, rapid rotation, deep atmospheres, rings and lots of satellites.

15. Size Small planets: Mercury, Venus, Earth, Mars.
The small planets have diameters less than km.
Giant planets: Jupiter, Saturn, Uranus and Neptune.
The giant planets have diameters greater than km.
The giant planets are sometimes also referred to as gas giants.

16. Relative the the Sun Inner planets: Mercury, Venus, Earth and Mars.
Outer planets: Jupiter, Saturn, Uranus, Neptune.
The asteroid belt between Mars and Jupiter forms the boundary between the inner solar system and the outer solar system.

17. Relative the the Earth Inferior planets: Mercury and Venus.
closer to the Sun than Earth.
The inferior planets show phases like the Moon's when viewed from Earth.
Earth.
superior planets: Mars thru Neptune.
farther from the Sun than Earth.
The superior planets always appear full or nearly so.

18. History
Classical planets: Mercury, Venus, Mars, Jupiter, and Saturn. Known since prehistorical times. Visible to the unaided eye
Modern planets: Uranus, Neptune. Discovered in modern times. Visible only with optical aid (telescopes)
The IAU has recently decided that "classical" should refer to all eight planets (Mercury thru Neptune, including Earth but not Pluto). This is contrary to historical usage but makes some sense from a 21st century perspective.

19. Origin of the Solar System
The Solar System is believed to have formed according to the nebular hypothesis, first proposed in 1755 by Immanuel Kant and independently formulated by Pierre-Simon Laplace.

20. Origin of the Solar System
This theory holds that 4.6 billion years ago the Solar System formed from the gravitational collapse of a giant molecular cloud. This initial cloud was likely several light-years across and probably birthed several stars.

21. Origin of the Solar System
About 4.5 billion years ago it is believed that the Solar System consisted of a large cloud of gas and dust, called a nebula.
This cloud started rotating, and the dust particles combined to form planetesimals. As the cloud rotated faster, it flattened, and the planetesimals formed.
The Sun is at the center, and secondly, the planets in orbit around the Sun. This model explains qualitatively many features of the Solar System, including the fact that the planets essentially all revolve around the Sun in the same plane.

22. Nebular Hypothesis of Solar System Formation.
To view this animation, click “View” and then “Slide Show” on the top navigation bar.

23. The Solar System – the Relative Sizes of the Planets

24. The Terrestrial Planets
Terrestrial planets seem to have experienced a similar early history, with extensive volcanism, cratering, and internal differentiation
Each has a metallic core and a silicate mantle crust, and shows evidence of continuing lava flows and meteorite impact
Outgassing produced an atmosphere as light gases from the interior rose to the surface during volcanism

25. MERCURY
Mercury, the planet nearest the Sun, is the second smallest planet in our solar system. It is only slightly larger than the Earth's moon. The surface is covered with craters. This tiny planet does not have any rings or moons.
Evidence of
craters
Average distance from Sun AU (57,909,175 km)
Rotation period (length of day in Earth days) Revolution period (length of year in Earth days) 87.97
Mercury's orbit is so close to the Sun that it is difficult to see. This explains why some early astronomers didn’t see it. Viewed from Earth, Mercury is never far from the Sun in the sky. Because the Sun is so bright, Mercury can only be seen in twilight.
Timocharis made the first recorded observation of Mercury in 265 BC
Atmospheric components trace amounts of hydrogen and helium
Surface materials are basaltic and anorthositic rocks and regolith

26. MERCURY Diameter: one third the size of Earth Distance: 0.4 AU
Atmosphere: no atmosphere
Features: Craters with smooth plains and most extreme temperature range
No life because of atmosphere
No moons or satellites

27. Mercury Closest to the sun.
Temperature ranges from 427°C in daylight to -173°C at night.
Revolves slowly, in two Mercury years three Mercury days will have passed.
One third the size of the Earth.
Period of Rotation = 88 days
Period of Revolution = 59 days

28. Mercury Missions
Environment, Geochemistry, and Ranging (MESSENGER) is the first mission sent to orbit the planet closest to the sun.
On Oct. 6, 2008, the probe flew by Mercury for the second time this year, using the planet’s gravity for a critical assist needed to keep the spacecraft on track for its orbit insertion around the planet three years from now.

29. VENUS
lava flows
impact craters
Venus is one of the brightest objects in our sky, so it is clearly visible to the naked eye. It can be tricky to spot because it is always near the Sun.
It rises and sets with the Sun each day.
Ancient civilizations believed Venus was actually two different objects, so they called the one that rose the Morning Star, and the one that set the Evening Star.
Average distance from Sun AU (108,208,930 km)
Rotation period (length of day in Earth days) (retrograde)
Revolution period (length of year in Earth days) 224.7
Atmospheric components 96% carbon dioxide, 3% nitrogen, 0.1% water vapor
Surface materials- basaltic rock and altered materials
Since Venus can be seen with the naked eye, no one really knows who discovered Venus. Venus’ beautiful color made it easy for ancient astronomers to find it in the night sky long before the invention of the telescope.
Interesting Facts About Venus
In the 1950's astronomers noticed that Venus rotates in the opposite direction of Earth. On Venus, the Sun rises in the west and sets in the east. Hottest planet in our solar system.
A canyon on Venus is four times as big and twice as deep as the Grand Canyon.
Venus probably once had oceans, but they all boiled away into the atmosphere.

30. VENUS Period of Rotation = 108.2 days Period of Revolution = 243 days
Almost same size as the Earth.
Hottest surface in our solar system. The average daytime surface temperature is 464°C, compared to the Earth’s 15°C.
This is hot enough to melt lead.
Named for the Roman goddess of love and beauty. Originally the Greek goddess Aphrodite.

31. VENUS Missions
Venus is covered by a thick layer of clouds that extends between 45 and 70 km above the surface. These rapidly-moving clouds are mainly composed of micron-sized droplets of sulphuric acid and other aerosols (fine solid or liquid droplets suspended in a gas), the origin of which is unknown.
Venus Express is ESA’s first mission to Venus. Launched in November 2005, the spacecraft arrived at the planet on 11 April 2006 and began science observations within a month. Since then, it has continuously been making new discoveries and revising our knowledge of Venus.

32. EARTH and MOON What similarities and differences do you notice
between the Earth and the
Moon?
Why do they have such
different surface features?
Average distance from Sun 1 AU (149,597,890 km) Rotation period (length of day in Earth days) 1 (23.93 hours) Revolution period (length of year in Earth days)
Atmospheric components 78% nitrogen, 21% oxygen, 1% argon Surface materials basaltic and granitic rock and altered materials

33. MARS
Mars is very bright, which makes it easy to spot in the night sky. It was named after
the Roman god of war because its reddish color reminded the people of blood.
Olympus Mons is the largest volcano in our solar system!
Although people have
never landed on Mars,
we have sent robotic
explorers there.
Average distance from Sun AU (227,936,640 km)
Rotation period (length of day in Earth days) 1.026
Revolution period (length of year in Earth days)
Atmospheric components 95% carbon dioxide, 3% nitrogen, 1.6% argon
Surface materials- basaltic rock and altered materials
Discovery
Since Mars is so bright and easy to see with the naked eye, we don't know who exactly discovered Mars. Ancient astronomers could see it long before the invention of telescopes.
Missions to Mars
Mariner 4, 6, 7, & 9 Viking I & II Mars Observer Mars Pathfinder Mars Global Surveyor Mars Polar Lander
Interesting Facts About Mars
Mars has the tallest mountain (Olympus Mons) in the solar system, three times the size of Mt. Everest. Mars’s moons, which are shaped like potatoes, probably used to be asteroids.
Martian crater

34. Mars Mars is the Latin name for Ares, the Greek god of war.
Mars has an atmosphere that is mainly carbon dioxide.
It is very thin, only 0.01 atmosphere’s at the surface.
Mars even has clouds, but they are thin also.
The winds can create dust storms that cover much of the planet and last for months.

35. A surprising find made by Mariner 9 was the existence of several canyons that are much larger than Earth’s Grand Canyon. The largest, Valles Marineris, is thought to have formed by slippage of material along huge faults in the crustal layer. In this respect, it would be comparable to the rift valleys of Africa.

36. Mars Mars has two very small moons, Phobos and Diemos.
They are named after the horses that pulled Mars’s chariot.
The larger Deimos is only 23-km in diameter.
Mars is about half the size of the Earth.
A 100 pound sixth grader would weigh 39 pounds on Mars.
It is very cold on Mars, with the average temperature ranging from -140° C to 20° C.

37. Mars Period of Rotation = 108.2 days Period of Revolution = 243 days
Mars surface has a wide variety of landscapes.
Olympus Mons is the largest volcano in our solar system. Its base would cover the state of Colorado.
It is three times taller than Mt. Everest.
There are many other volcanoes on Mars, but none seem to be active at this time.

38. Mars Missions
There have been many missions to Mars, starting with the Viking craft in 1976.
There are currently two orbiters and two rovers collecting data on Mars.
Manned missions are also currently being planned, around 2025 or so.

39. Mars Missions
Next NASA Mars Mission Rescheduled For NASA's Mars Science Laboratory will launch two years later than previously planned, in the fall of The mission will send a next-generation rover with unprecedented research tools to study the early environmental history of Mars.
The composition and markings of some Martian rocks indicate that liquid water was once present on Mars’s surface. The marking shown in the center of the rock, however, was created by a NASA rover during chemical analysis.

40. ASTEROID BELT
Most asteroids can be found in the Asteroid Belt, which is located between
Mars and Jupiter. Asteroids are rocky and metallic objects that orbit the Sun,
but are too small to be considered planets. They are known as minor planets.
Asteroids range in size from Ceres, which has a diameter of about 1000 km,
down to the size of pebbles.
Asteroids are sometimes called Minor planets. They are small rocky bodies.
They are made up of leftover material from our solar system.
Largest asteroid 1 Ceres Total discovered to date Over 250,000 designations have been assigned by the Minor Planet Center; over 100,000 have been observed more than once. Total numbered asteroids to date.Over 30,000. Near-Earth asteroids Around 1.0 AU from earth, with perihelia less than or equal to 1.3 AU.

41. The main asteroid belt occupies the orbit between Mars and Jupiter, between 2.3 and 3.3 AU from the Sun.

42. Asteroid Belt: Ceres
Ceres (2.77 AU) is the largest body in the asteroid belt and its only dwarf planet. It has a diameter of slightly under 1000 km, large enough for its own gravity to pull it into a spherical shape. Ceres was considered a planet when it was discovered in the 19th century, but was reclassified as an asteroid in the 1850s as further observation revealed additional asteroids. It was again reclassified in 2006 as a dwarf planet.

43. Gas Giants
Separated from the 1st zone by the asteroid belt, the 2nd Zone contains the gas giants.
Made of the lightweight elements Hydrogen, Helium, Carbon, Oxygen, and Nitrogen.
All are much larger than the Earth, with times the mass, and 4-11 times the diameter.
Not believed to have solid surfaces.
Have rings and many satellites.

44. JUPITER
Jupiter, the fifth planet from the Sun, is the largest planet in our solar system.
Jupiter is so big that over 1,000 planets the size of Earth could fit into it.
It has over 60 moons and 2 rings.  Can life exist on Jupiter's moon, Europa?
The “Great Red Spot”
Is actually a huge
Storm system!
average distance from Sun AU (778,412,020 km)
Rotation period (length of day in Earth days) 0.41 (9.8 Earth hours)
Revolution period (length of year in Earth years) 11.86
Discovery
Jupiter is the largest planet in our solar system, and it is one of the brighter objects in the night sky. No one knows for sure who discovered Jupiter, but we know the ancient Greeks named it after the god, Zeus.
Missions to Jupiter
Pioneer 11 (USA) April 6, 1973
Pictures of Jupiter and its Great Red Spot
Voyager 1 (USA) September 5, 1977
Photographs and information on Jupiter's many moons.
Voyager 2 (USA) August 20, 1977
Found that Jupiter's Great Red Spot is really a complex storm.
Found that Io, one of Jupiter's moons, has active volcanoes.
Galileo (USA and Europe) October 18, 1989
Entered Jupiter's atmosphere.
Interesting Facts About Jupiter
Largest planet in our solar system
Has the largest moon in our solar system
Shortest day
Largest storm (Great Red Spot) three times the size of Earth
Pressure on Jupiter is so great it would crush a spaceship
Here are a few of Jupiter’s moons

45. Jupiter Named for Jove, the King of the Roman Gods.
Roman name for the Greek god Zeus.
Often the term Jovian is used to describe things pertaining to Jupiter. Example: the Jovian moons.

46. Jupiter
Believed to be a failed star, lacking the mass to become a small star.
Most massive planet in solar system.
Has over 60 satellites.
Density is 1.33g/cm3.
Rotates every 10 hours.
Takes 12 years to orbit the sun.
Gravity almost 2.5 times that of the Earth.

47. Jupiter
The red spot is a huge storm that has been continuously going on Jupiter for over 400 years.  Winds inside this storm reach speeds of about 270 mph.  With a diameter of 15,400 miles, this storm is almost twice the size of the entire Earth.
Period of Rotation = days
Period of Revolution = years

48. Moons of Jupiter
The New Horizons Long Range Reconnaissance Imager (LORRI) captured these two images of Jupiter's outermost large moon, Callisto, as the spacecraft flew past Jupiter in late February. New Horizons' closest approach distance to Jupiter was 2.3 million kilometers (1.4 million miles), not far outside Callisto's orbit, which has a radius of 1.9 million kilometers (1.2 million miles).
However, Callisto happened to be on the opposite side of Jupiter during the spacecraft's pass through the Jupiter system, so these images, taken from 4.7 million kilometers (3.0 million miles) and 4.2 million kilometers (2.6 million miles) away, are the closest of Callisto that New Horizons obtained.

50. SATURN
Saturn, the sixth planet from the Sun, is the second largest planet in our solar system.
It is often called the ringed planet because many rings of dust and rocks surround it.
Saturn also has over 31 moons.
Saturn with some of
its moons
Some of Saturn’s rings
Average distance from Sun AU (1,426,725,400 km)
Rotation period (length of day in Earth days) 0.44 (10.2 Earth hours)
Revolution period (length of year in Earth years) 29.46
Discovery Saturn is clearly visible in the night sky. The ancient Greeks named the planet after the god of agriculture and time. It wasn't until 1655, however, that we knew Saturn had rings. Galileo saw them, but he didn't know what they were. Another astronomer, Christian Huygens, later discovered they were rings.
Missions to Saturn:
Pioneer 11 (USA) April 6, 1973
Took pictures of Saturn. Discovered new rings and moons.
Voyager 1 (USA) September 5, 1977
Took pictures of Saturn's moons. Discovered how complex Saturn’s rings were.
Voyager 2 (USA) August 20, 1977
Took pictures of Saturn's moons.
Cassini (USA, European Space Agency, Italy) October 13, 1997
Experiments will help scientists understand Saturn's moons, rings, and atmosphere. Will send a probe into Titan's atmosphere.
Interesting Facts About Saturn
Has the most moons Has thousands of rings made of ice, dust, and rocks The farthest planet you can see without a telescope The planet would float if you put it in water
Atmospheric components 97% hydrogen, 3% helium, .05% methane Rings Rings are 270,000 km in diameter, but only a few hundred meters thick. Particles are centimeters to decameters in size and are ice (some may be covered with ice); there are traces of silicate and carbon minerals. There are four main ring groups and three more faint, narrow ring groups separated by gaps called divisions.
Titan is a moon of Saturn that may have some
Conditions necessary for life! The picture on
the right shows an artist’s drawing of how Titan
might have looked when the Cassini-Huygen’s
probe dropped into its atmosphere in Dec., 2004.

51. Saturn Saturn was the Roman God of the Harvest and of Time.
Father of Jupiter, Neptune, and Pluto.
The Roman name for the Greek god Cronos.
Saturnalia was the mid-winter festival in Saturns honor. It lasted seven days, and there was much merrymaking. Public business was suspended and schools were closed. Parents gave presents to their children.

52. Saturn 2nd largest planet in solar system.
A “day” on Saturn is a little over 10 hours long!
It takes 29 years to orbit the sun.
Almost 10 times larger than Earth.
Most visible rings of any planet.
Density is 0.69 g/cm3.
If a large enough ocean could be found, Saturn would float in it!
Period of Rotation = 1,427 days
Period of Revolution = years

53. URANUS
Uranus is a very unusual planet because it sits on its side with north and south
poles sticking out the sides. It rotates around this axis, making it look like a ball
rolling around in a circle around the Sun.
Average distance from Sun AU (2,870,972,200 km)
Rotation period (length of day in Earth days) 0.72 (17.9 Earth hours)(retrograde)
Revolution period (length of year in Earth days) 30,685 (84 Earth years)
Atmospheric components 83% hydrogen, 15% helium, 2% methane (at depth)
Rings Uranus has a system of narrow, faint rings. Ring particles are dark, and could consist of rocky or carbonaceous material.
Discovery
Astronomer William Herschel discovered Uranus in Using a telescope, he spotted a dim object. He watched it for years and decided it had to be a planet given its orbit.
Herschel also discovered two of Uranus’ moons in Voyager II spotted many of its other moons in 1986.
In 1977, scientists saw Uranus blink several times. They later discovered that rings surrounding the planet caused the blinking. These rings are very dark and narrow, unlike Saturn's, which are bright and colorful. Voyager II sent back many pictures that clearly show these rings.
Missions to Uranus
Voyager 2 (USA) August 20, 1977
Took thousands of pictures of Uranus, its rings, and its moons.
Interesting Facts About Uranus
Herschel argued with other astronomers over the new planet's name. He wanted to name it after King George III of Great Britain. Other astronomers wanted him to name it after himself. Uranus was named after Ouranos, one of the first gods in Greek mythology. Uranus’ moons have names from Shakespearean plays. Since Uranus lies nearly on its side, its North Pole gets 42 years of daylight while the South Pole gets 42 years of darkness. Uranus’ rings might have formed from broken moons.
some of Uranus’s moons
Black rings

54. Uranus
URANUS: Great primeval God of the Sky. Born of GAIA, the Earth, he covered the world in the form of a vast bronze dome and ruled over everything.

55. Uranus Diameter is like 4 Earth’s. Mass is 14.5 Earth’s.
Takes 84 years to revolve around the sun.
Day is a little over 17 hours long.
Has more than 20 moons.

56. Uranus Axis
Uranus is considered unusual because the planet is tipped on its side. The poles actually point towards the Sun. This is due to the fact that its magnetic field is tilted 60 degrees from the axis of rotation.
It is believed that Uranus was struck by a large object that knocked Uranus on its side.

57. NEPTUNE
Neptune, usually the eighth planet from the Sun, is a very cold place.
Occasionally, Pluto crosses Neptune’s orbit and becomes the eight planet.
Its bluish color comes from its atmosphere of methane gas.
average distance from Sun AU (4,498,252,900 km)
Rotation period (length of day in Earth days) 0.67 (19.1 hours)
Revolution period (length of year in Earth days) 60,190 (164.8 Earth years)
Atmospheric components 74% hydrogen, 25% helium, 1% methane (at depth)
Rings are narrow, and contain concentrations of particles called ring arcs.
Discovery
Neptune wasn't discovered the way all the other planets in our solar system were found. Astronomers didn't scan the sky with their powerful telescopes to find Neptune. They used math instead!
After the discovery of Uranus, astronomers were having trouble figuring out Uranus’ orbit. They realized that there must be another planet farther out than Uranus because this unknown planet’s gravitational pull slightly changes Uranus' orbit. They were right! French astronomer Leverrier and English astronomer John Couch Adams made the mathematical calculations of where Neptune should be in 1843, and German astronomer Johann Galle found it in 1846.
Missions to Neptune
Voyager 2 (USA) August 20, 1977
Took thousands of pictures of Neptune, its rings, and its moons.
Interesting Facts About Neptune
Neptune was actually the farthest planet from the Sun from February 7, 1979 until February 11, 1999 (the order was Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Pluto, and Neptune). Neptune will be the 8th farthest planet from the Sun until the 23rd century. Neptune’s Great Dark Spot is a huge storm the size of Earth.
Tiny Dark Moon

58. Neptune Neptune is the Roman god of the sea.
The Romans modeled him after the Greek god Poseidon.

59. Neptune Neptune revolves on its axis every 18 hours.
It takes 165 years to revolve around the sun once.
Has the mass of 17 Earths.
Has 13 moons.
Diameter is almost 4 times larger than Earths.
Blue-green color is from the methane in the atmosphere.
At times it is the furthest planet from the sun.

60. Neptune Diameter: 4 times the size of Earth Distance: 30 Au
Atmosphere: 80% Hydrogen 19% Helium 1.5% Methane
Features: At times it is the furthest planet from the sun. Icy clouds and enormous storms
Life:possible life on one of its moons called Triton

61. PLUTO
Pluto, usually the ninth planet from the Sun, is the smallest planet in our solar system.
Some scientists believe that Pluto once was one of Neptune’s moons, and that it
pulled out away from Neptune and made its own orbit.
Average distance from Sun AU (5,906,376,200 km)
Rotation period (length of day in Earth days) 6.39 (retrograde)
Revolution period (length of year in Earth years)  247.92
Atmospheric components perhaps methane and nitrogen
Surface materials perhaps methane ice
Discovery: After the discovery of Neptune in 1846, scientists believed that there still might be a ninth planet, and they set out to find it. Finding Pluto was difficult. Pluto is very small, it is a long way from the Sun, and it is very dim in the sky. The planet moves very slowly, taking 248 years to complete its orbit around the Sun, so it took many years before Pluto’s motion could help identify it. An amateur American astronomer, Clyde Tombaugh, finally found Pluto in 1930.
Missions to Pluto
Pluto is the only planet that has not been visited by a spacecraft from Earth. The Pluto Express probe has been delayed.
Interesting Facts About Pluto
Pluto was not the farthest planet from the Sun from February 7, 1979 until February 11, 1999 (the order was Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Pluto, and Neptune). Pluto will be the farthest planet from the Sun until the 23rd century. Pluto’s moon, Charon, is very close to Pluto and about the same size.
Clearest view to date
Of Pluto and Charon

62. Pluto Usually the furthest planet from the sun.
2/3rds the size of our moon.
Has one moon, Charon.
So cold that oxygen and nitrogen in its atmosphere is frozen solid.
Only planet not visited by a spacecraft.
Pluto takes 248 years to make one orbit around the sun!

63. Pluto
When Pluto comes close enough to the sun, the surface of solid Nitrogen sublimates to produce a substantial atmosphere with winds and clouds.
Because the planet is so small, however, it does not have enough gravity to bind an atmosphere for very long. Thus Pluto's atmosphere is being rapidly produced and rapidly lost at the same time.
This means that the atmosphere is not in equilibrium.

64. Pluto
Pluto (39 AU average), a dwarf planet, is the largest known object in the Kuiper belt.
When discovered in 1930 it was considered to be the ninth planet; this changed in 2006 with the adoption of a formal definition of planet.

65. New Horizons Pluto Kuiper Belt Flyby
Pluto has a relatively eccentric orbit inclined 17 degrees to the ecliptic plane and ranging from 29.7 AU from the Sun at perihelion (within the orbit of Neptune) to 49.5 AU at aphelion.
The mission is expected to arrive
at Pluto sometime in 2015.

66. COMETS Comets are sometimes called dirty snowballs or "icy mudballs".
They are a mixture of ices (both water and frozen gases) and dust that for
some reason didn't get incorporated into planets when the solar system was formed.
This makes them very interesting as samples of the early history of the solar system.
Comets have
elliptical orbits.
Comets are icy planetesimals formed in the outer solar system.
They are composed mainly ice and dust
They have highly elliptical orbits which take them very close to the Sun and back out into deep space, often far beyond the orbit of Pluto. Their orbit duration can be from less than 200 years to more than several millions of years.
Composition of comets:
Nucleus- Main body of the comet: composed of dust particles trapped in a mixture of ices of water, carbon monoxide, carbon dioxide, methane, and ammonia. Typically only a few kilometers in diameter
Coma- A halo of evaporated gas and dust which forms when the comet approaches the inner solar system. The coma grows larger as the comet gets closer to the sun.
When we see a comet, we
are seeing the tail of the comet
as comes close to the Sun.
Comet Halley in 1910

67. Kuiper belt
The Kuiper belt, the region's first formation, is a great ring of debris similar to the asteroid belt, but composed mainly of ice. It extends between 30 and 50 AU from the Sun. This region is thought to be the source of short-period comets, such as Halley's Comet.
It is composed mainly of small solar system bodies, but many of the largest Kuiper belt objects, such as Quaoar, Varuna, and Orcus, may be reclassified as dwarf planets.