PLANETIA
INTRO
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The solar system has been a popular subject for school children ever since it was first taught. Learning about the planets brings up images of far away worlds with exotic landscapes, alien skies, and horrific weather patterns. California State Polytechnic University has created a monument to these great worlds. The sun and all nine planets have been immotalized in bronze and placed throughout the campus. Starting at the Student Union, where the center of the solar system resides, the sun, you take a tour of all nine planets. Each planet is situated an appropriate distance from the sun to show the tru scale of our small part of the universe. have fun, take you time, and explore the solar system and Cal Poly's beautiful campus.
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SUN T
he sun in the center of our planetary system. It is the source of our heat, our light, and our life. Without it we wouldn't be here. This is the starting point for life and for this tour. The sun contains over 98% of the mass in the solar system. You could fit 109 Earths across the face of the sun. It's simply huge. Solar energy is created in the center of this ball of hydrogen. The enegry in created by nuclear fusion of four Hydrogen nucleii. This happens in immense pressure. The ebergy release is heat and light.
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MERCURY M
Facts: Diameter: 3032 mi. 21 Mass: 0.364x10 kg Gravity: 12.1 ft/s 2 Distance from Sun: 36,000,000 mi. Length of Day: 4222.6 hrs Length of Year: 88 days Mean Temp: 333o F Tilt of Axis: 0.01o Atm. Pressure: 0 atm. 42% Atmosphere: He Na 42% O2 15% Other 1%
ercury was named by the Romans after the fleet-footed messenger of the gods because it seemed to move more quickly than any other planet. It is the closest planet to the Sun, and second smallest planet in the solar system. Its diameter is 40% smaller than Earth and 40% larger than the Moon. It is even smaller than Jupiter's moon Ganymede and Saturn's moon Titan. If an explorer were to step onto the surface of Mercury, he would discover a world resembling lunar terrain. Mercury's rolling, dust-covered hills have been eroded from the constant bombardment of meteorites. Fault-cliffs rise for several kilometers in height and extend for hundreds of kilometers. Craters dot the surface. The explorer would notice that the Sun appears two and a half times larger than on Earth; however, the sky is always black because Mercury has virtually no atmosphere to cause scattering of light. As the explorer gazes out into space, he might see two bright stars in the distance. One appearing as cream colored Venus and the other as blue colored Earth.
Mythology: Mercury was the son of Jupiter, the king of the gods, and Maia, a minor goddess. Mercury was the messenger of the gods and the god of roads and travel in Roman mythology. The Romans considered Mercury rather crafty and deceptive, even a trickster or thief. Criminals considered him their protector. Mercury resembled the Greek god Hermes. He delivered his messages with a miraculous speed because he wore winged sandals.
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Until Mariner 10, little was known about Mercury because of the difficulty in observing it from Earth telescopes. At maximum elongation it is only 28 degrees from the Sun as seen from Earth. Because of this, it can only be viewed during daylight hours or just prior to sunrise or after sunset. When observed at dawn or dusk, Mercury is so low on the horizon that the light must pass through 10 times the amount of Earth's atmosphere than it would if Mercury was directly overhead. During the 1880's, Giovanni Schiaparelli drew a sketch showing faint features on Mercury lie determined
Mercury lie determined that Mercury must be tidally locked to the Sun, just as the Moon is tidally locked to Earth. In 1962, radio astro-nomers looked at radio emissions from Mercury and determined that the dark side was too warm to be tidally locked. It was expected to be much colder if it always faced away from the Sun. In 1965, Pettengill and Dyce determined Mercury's period of rotation to be 59 +/- 5 days based upon numerous radar observations.
VENUS V
enus, the jewel of the sky, was once know by ancient astronomers as the morning star and evening star. Early astronomers once thought Venus to be two separate bodies. Venus, which is named after the Roman goddess of love and beauty, is veiled by thick swirling cloud cover. Astronomers refer to Venus as Earth's sister planet. Both are similar in size, mass, density and volume. Both formed about the same time and condensed out of the same nebula. However, during the last few years scientists have found that the kinship ends here. Venus is very different from the Earth. It has no oceans and is surrounded by a heavy atmosphere composed mainly of carbon dioxide with virtually no water vapor. Its clouds are composed of sulfuric acid droplets. At the surface, the atmospheric
surface, the atmospheric pressure is 92 times that of the Earth's at sea-level. Venus is scorched with a surface temperature of about 4820 C (9000 F). This high temperature is primarily due to a runaway greenhouse effect caused by the heavy atmosphere of carbon dioxide. Sunlight passes through the atmosphere to heat the surface of the planet. Heat is radiated out, but is trapped by the dense atmosphere and not allowed to escape into space. This makes Venus hotter than Mercury. A Venusian day is 243 Earth days and is longer than its year of 225 days. Oddly, Venus rotates from east to west. This means that the Sun rises in the west and sets in the east. Until just recently,
Until just recently, Venus' dense cloud cover has prevented scientists from uncovering the geological nature of the surface. Developments in radar telescopes and radar imaging systems orbiting the planet have made it possible to see through the cloud deck to the surface below. Four of the most successful missions in revealing the Venusian surface are NASA's Pioneer Venus mission (1978), the Soviet Union's Venera 15 and 16 missions (1983-1984), and NASA's Magellan radar mapping mission (IQYO-l994). As these spacecraft began mapping the planet a new picture of Venus emerged. Venus' surface is relatively young geologically speaking. It appears to have been completely resurfaced 300 to 500 million years ago. Scientists debate how and ' k this occurred. The Venusian topography consists of vast plains covered by lava t1os and mountain or highland regions deformed by geological activity. Maxwell Montes is the highest peak on Venus. The Aphrodite Terra highlands extend almost half ay around the equator. Magellan images of highland regions above 2.5 kilometers (1.5 miles) are unusually bright, characteristic of moist soil. However, liquid water does not exist on the surface and cannot account for the bright highlands. One theory suggests that the bright material might he composed of metallic compounds. shown the material might be iron pyrite (also know
Facts: Diameter: 7521 mi. 21 Mass: 5.37 x10 kg Gravity: 29.1 ft/s 2 Distance from Sun: 67,200,000 mi. Length of Day: 2802 hrs Length of Year: 224.7 days Mean Temp: 867o F Tilt of Axis: 177.4o Atm. Pressure: 91 atm. Atmosphere: CO2 97% N2 3%
Mythology: Venus was originally was the goddess of love and beauty, but later also symbolized the creative force that sustains all life. Venus was the mother of Aeneas, an ancestor of the founders of Rome. Venus was born full-grown from the foam of the Mediterranean Sea. In spite of her beauty, she married the lame blacksmith god Vulcan, but later fell in love with the god of war, Mars. Their child, Cupid, was the god of love.
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EARTH F
Facts: Diameter: 7926 mi. Mass: 6.58x10 kg Gravity: 32.1 ft/s 2 Distance from Sun: 93,000,000 mi. Length of Day: 24 hrs Length of Year: 365.24 days Mean Temp: 59o F Tilt of Axis: 23.5o Atm. Pressure: 1 atm. 77% Atmosphere: N 2 O2 21% Other 2%
rom the perspective we get on Earth, our planet appears to be big and sturdy with and endless ocean of air. From space, astronauts often get the impression that the Earth is small with a thin, fragile layer of atmosphere. For a space traveler, the distinguishing features of Earth are the blue oceans of water, the brown and green landmasses, and white clouds set against a black background. Many dream of traveling in space and viewing the wonders of the universe. In reality all of us are space travelers. Our spaceship is the planet Earth, traveling at he speed of 67,000 miles per hour. Earth is the 3rd planet from the sun at a distance of 93 million miles. It takes 365.24 days for the Earth to travel around the sun, and 24 hours to make a complete revolution. Earth is 7926 mils wide, only slightly larger than Venus. Our atmosphere is mainly Nitrogen and Oxygen, with trace amounts of other gases. Earth is the only planet known to harbor life. The planet's rapid spin and molten core give rse to an extensive magnetic field, which, along with the
Mythology: Earth is considered the body of Gaea, the goddess wife of Uranus. She is associated with the mother role. She bore the Titans, the first mythological race of beings, but Uranus feared them and confined them within Gaea. To get revenge, Gaea planned an attack on Uranus. Cronus attacked him with a sickle and wounded him, making him unable to father more children. Because of this wound he became forever separated from Gaea.
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atmosphere, shields us from nearly all harmful radiation coming from the sun and other stars. Earth's atmosphere also prtects us from meteors, most of which burn up before they strike the planet's surface. From our journeys into space, we have learned much about our home planet. The first American satellite, Explorer 1, discovered an intense radiation zone, now called the Van Allen radiation belts. This layer is formed from rapidly moving charged particals that are trapped by the Earth's magnetic field in a doughnut-shaped region surrounding the equator. Other findings frm satellites show that our
satellites show that our planet's magnetic field is distorted into a tear-drop shape by the solar wind. We also now know that our wispy upper atmosphere, once believed calm and uneventful, seethes with activity - swelling by day and contracting by night. Affected by changes in solar activity, the upper atmosphere contributes to weather and climate on Earth. Besides affecting Earth's weather, solar activity gives rise to a visual phenomenon, the Aurora.
MARS M
ars is the fourth planet from the Sun arid is commonly referred to as the Red Planet. The rocks, soil and sky have a red or pink hue. The distinct red color was observed by stargazers throughout history. It was given its name by the Romans in honor of the god of war. Other civilizations have had similar names. The ancient Egyptians named the planet Her Descher meaning the red one. Before space exploration. Mars was considered the best candidate for harboring extraterrestrial life. Astronomers thought they saw straight lines crisscrossing its surface. This led to the popular belief that irrigation canals on the planet had been constructed by intelligent beings. In 1938, when Orson Welles broadcasted a radio
broadcasted a radio drama based on the science fiction classic War of the Worlds by H.G. Wells, enough people believed in the tale of invading Martians to cause a near panic. Another reason for scientists to expect life on Mars had to do with the apparent seasonal color changes on the planet's surface. This phenomenon led to speculation that conditions might support a bloom of Martian vegetation during the warmer months arid cause plant life to become dormant during colder periods. In July of 1965, Mariner 4, transmitted 22 close-up pictures of Mars. All that was revealed was as a surface containing many craters and naturally occurring channels but no
channels but no evidence of artificial canals or flowing water. Finally, in July and September 1976, Viking Landers 1 and 2 touched down on the surface of Mars. The three biology experiments aboard the landers discovered unexpected and enigmatic chemical activity it m the Martian soil, but provided no clear evidence for the presence of living microorganisms in the soil near the landing sites. According to mission biologists. Mars is self-sterilizing. They believe the combination of solar ultraviolet radiation that saturates the surface, the extreme dryness of the soil and the oxidizing nature of the soil chemistry prevent the formation of living organisms in the Martian soil. The question of life on Mars at some time in the distant past remains open. Other instruments found no sign of organic chemistry at either landing site, but they did provide a precise and definitive analysis of the composition of the Martian atmosphere and found previously undetected trace elements in both the soil and the gases in the atmosphere. The atmosphere of Mars is quite different from that of Earth. It is composed primarily of carbon dioxide with small amounts of other gases. Martian air contains only about 1/1,000 as much water as our air, but even this small amount can condense out, forming clouds that ride high in the atmosphere or swirl around the slopes of huge towering volcanoes.
Facts: Diameter: 4222 mi. 21 Mass: 0.708x10 kg Gravity: 12.1 ft/s 2 Distance from Sun: 141,600,000 mi. Length of Day: 24.7 hrs Length of Year: 687 days Mean Temp: -85o F Tilt of Axis: 25.2o Atm. Pressure: 0.01 atm. Atmosphere: CO2 95.3% N2 2.7% Ar 1.6% Other 0.4%
Mythology: Mars was the god of war in Roman mythology. He was given special importance because he was considered the father of Romulus and Remus, the legendary founders of Rome. Originally Mars was the god of farmland and fertility, but after the Romans came into contact with the Greeks he was likened to Aries, the Greek god of war. The Romans would pray to Mars before going into battle, and if the were the victors, would give Mars some of the spoils.
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JUPITER J
Facts: Diameter: 88,846 mi. 21 Mass: 2093x10 kg Gravity: 75.9 ft/s2 Distance from Sun: 483,800,000 mi. Length of Day: 9.9 hrs Length of Year: 4331 days Mean Temp: -166o F Tilt of Axis: 3.1o Atm. Pressure: 0.01 atm. 90% Atmosphere: H2 He 10%
upiter is the fifth planet from the Sun and is the largest one in the solar system. If Jupiter were hollow, more than one thousand Earths could fit inside. It also contains more matter than all of the other planets combined. It has a mass of 1.9 x 10 27 kg and is 142.800 kilometers (88,736 miles) across the equator. Jupiter possesses 28 know satellites, four of which Callisto, Europa, Ganymede and to - were observed by Galileo as long ago as 1610. Another 12 satellites have been recently discovered and given provisional designators until they are officially confirmed and named. There is a ring system, but it is very faint and is totally invisible from the Earth. (The rings were discovered in 1979 by Voyager I.) The atmosphere is very deep, perhaps comprising the whole planet, and is somewhat like the Sun. It is composed mainly of hydrogen and helium, with small amounts of methane, ammonia, water vapor and other compounds. At great depths within Jupiter, the pressure is so great that the hydrogen atoms are broken up and the electrons are freed so that the resulting atoms consist of bare protons. This produces a state in which the hydrogen
Mythology: Jupiter was the king of the gods and the ruler of the univers in Roman mythology. Jupiter had the same powers as the Greek god Zeus. Jupiter was the son of Saturn, the ruler of the universe. Jupiter and the other sons of Saturn overthrew him and Jupiter took Saturn's place. Jupiter's bothers were Neptune and Pluto. His sisters were Ceres, Juno and Vesta. Jupiter married Juno. He was originally associated with thunder and lightning.
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protons. This produces a state in which the hydrogen element becomes metallic. Colorful latitudinal bands, atmospheric clouds and storms illustrate Jupiter's dynamic weather systems. The cloud patterns change within hours or days. The Great Red Spot is a complex storm moving in a counter-clockwise direction. At the outer edge, material appears to rotate in four to six days; near the center, motions are small and nearly random in direction. An array of other smaller storms and eddies can be found throughout the colorful banded clouds. Auroral emissions,
Auroral emissions, similar to Earth's northern lights, were observed in the polar regions of Jupiter. The auroral emissions appear to be related to material from to that spirals along magnetic field lines to fall into Jupiter's atmosphere. Cloud-top lightning bolts, similar to superbolts in Earth's high atmosphere, were also observed. Unlike Saturn's intricate and complex ring patterns, Jupiter has a simple ring system that is composed of three parts.
SATURN S
aturn is the sixth planet from the Sun and is the second largest in the solar system with an equatorial diameter of 119,300 kilometers (74.130 miles). Much of what is known about the planet is due to the Voyager explorations in 1980. Saturn is visibly flattened at the poles, a result of the very fast rotation of the planet on its axis. Its day is 10 hours, 39 minutes long, and it takes 29.5 Earth years to revolve about the Sun. The atmosphere is primarily composed of hydrogen with small amounts of helium and methane. Saturn is the only planet less dense than water (about 30 percent less). In the unlikely event that a large enough ocean could be found. Saturn would float in it. Saturn's hazy yellow hue is marked by broad atmospheric handing
atmospheric handing similar to, but fainter than that found on nearby Jupiter. The wind blows at high speeds on Saturn. Near the equator, it reaches velocities of 500 meters a second (1.100 miles an hour). The wind blows mostly in an easterly direction. The strongest winds are found near the equator and velocity falIs off uniformly at higher latitudes. At latitudes greater than 35 degrees., winds alternate east and west as latitude increases. Saturn's ring system makes the planet one of the most beautiful objects in the solar system. The rings are split into a number of different parts which include the bright A and B rings and a fainter C ring. The ring system has various gaps. The most
various gaps. The most notable gap is the Cassini Division, which separates the A and B rings. Giovanni Cassini discovered this division in 1675. The Encke Division, ss hich splits the A Ring, is named after Johann Encke, who discovered it in 1837. Space probes have shown that the main rings are really made up of a large number of narrow ringlets. The origin of the rings is obscure. It is thought that the rings may have been formed from larger moons that were shattered by impacts of comets and meteoroids. The ring composition is not known for certain, but the rings do show a significant amount of water. They may he composed of icebergs and or snowballs from a few centimeters to a few meters in size. Much of the elaborate structure of some of the rings is due to the gravitational effects of nearby satellites. This phenomenon is demonstrated by the relationship between the F-ring and two small moons that shepherd the ring material and keep the close. Radial, spoke-like features in the broad B-ring were also found by the Voyagers. The features are believed to be composed of fine, dust-size particles. The spokes were observed to to rill and dissipate in the time-lapse images taken by the Voyagers. While electrostatic charging may create spokes by levitating dust particles above the ring, the exact cause of the formation of the spokes is not well understood.
Facts: Diameter: 74,897 mi. 21 Mass: 627x10 kg Gravity: 29.4 ft/s 2 Distance from Sun: 890,800,000 mi. Length of Day: 10.7 hrs Length of Year: 10,747 days Mean Temp: -220o F Tilt of Axis: 26.7o 97% Atmosphere: H2 He 3%
Mythology: Saturn was an early god in Roman mythology. He was considered the god of fertility of planting. Each year the Romans honored Saturn with a week-long festival called Saturnalia. During this period schools and businesses remained closed, slaves and masters were equals, no wars could be started, no criminals could be punished, and most rules of public conduct were suspended. Modern traditions of feasts and gift giving during Christmas may have started here.
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URANUS U
Facts: Diameter: 31,763 mi. 21 Mass: 95.7x10 kg Gravity: 28.5 ft/s2 Distance from Sun: 1,784,800,000 mi. Length of Day: 17.2 hrs Length of Year: 30,589 days Mean Temp: -320o F Tilt of Axis: 97.8o 83% Atmosphere: H 2 He 15% NH4 2%
ranus is the seventh planet from the Sun and is the third largest in the solar system. It was dis-covered by WiIliam llerschel in 1781. It has an equatorial diameter of 5l,800 kilometers (32,190 miles) and orbits the Sun once every 84.01 Earth years. It has a mean distance from the Sun of 2.87 billion kilometers (1.78 billion miles). The length of a day on Uranus is 17 hours and 4 minutes. Uranus has at east 22 moons. The two largest moons, Titan a and Oheron, were discovered by William IIerschel in 1787. The atmosphere of Uranus is composed of 83% hydrogen, 15% helium, 2% methane and small amounts of acetylene and other hydrocarbons. Methane in the upper atmosphere absorbs red light, giving Uranus its blue-green color. The atmosphere is arranged into clouds running at constant latitudes, similar to the orientation of the more vivid latitudinal bands seen on Jupiter and Saturn. Winds at mid-latitudes on Uranus blow in the direction of the planet's rotation. These winds blow at velocities of 40 to 160 meters per second (90 to 360 miles per hour). Radio science experiments found winds of about 100
Mythology: Uranus was the earliest god of the sky in both Roman and Greek mythology. He was the husband of Gaea, the earth. They were the parents of the Titans. Uranus feared his children and confined them deep within their mother, the earth, immediately after their birth. Gaea, with the help of Cronus, her youngest son, wounded Uranus, making him unable to father any more children. He was then separated forever from Gaea.
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Recent radio science experiments found winds of about 100 meters per second blowing in the opposite direction at the equator. Uranus is distin-guished by the fact that it is tipped on its side. Its unusual position is thought to be the result of a collision with a planet-sized body early in the solar system's history. Voyager 2 found that one of the most striking influences of this side-ways position is its effect on the tail of the magnetic field, which is itself tilted 60 degrees from the planet's axis of rotation. The magnet-otail was shown to be twisted by the planet's rotation into a long corkscrew shape
corkscrew shape behind the planet. The magnetic field source is unknown; the electrically conductive super-pressurized ocean of water and ammonia once thought to lie between the core and the atmosphere now appears to be nonexistent. The magnetic fields of Earth and other planets are believed to arise from electrical currents produced in their molten cores. In 1977, the first nine rings of Uranus were discovered. During the Voyager encounters,
NEPTUNE N
eptune is the outermost planet of the gas giants. It has an equa-torial diameter of 49,500 kilometers (30,760 miles). If Neptune were hollow, it could contain nearly 60 Earths. Neptune orbits the Sun every 165 years. It has eight moons, six of which were found by Voyager. A day on Neptune is 16 hours and 6.7 minutes. Neptune was discovered on September 23, 1846 by Johann Gottfried Galle, of the Berlin Observatory, and Louis d'Arrest, an astronomy student, through mathematical pre-dictions made by Urbain Jean Joseph Le Verrier. The first two thirds of Neptune is composed of a mixture of molten rock, water, liquid ammonia and methane. The outer third is
a mixture of heated gases comprised of hydrogen, helium, water and methane. Methane gives Neptune its beautiful blue cloud color. Neptune is a dy-namic planet with several large, dark spots reminiscent of Jupiter's hurricane-like storms. The largest spot, known as the Great Dark Spot, is about the size of the earth and is similar to the Great Red Spot on Jupiter. Voyager revealed a small, irregularly shaped, eastwardmoving cloud scooting around Neptune every 16 hours or so. This scooter as it has been dubbed could be a plume rising above a deeper cloud deck. Long bright clouds, similar to cirrus clouds on Earth, were seen high in Neptune's atmo-sphere. At low
sphere. At low northern latitudes, Voyager captured images of cloud streaks casting their dark shadows on cloud decks below. The strongest winds on any planet were measured on Neptune. Most of the winds there blow westward, opposite to the rotation of the planet. Near the Great Dark Spot, winds blow up to 2,000 kilometers (1,200 miles) an hour. Neptune has a set of four rings which are narrow and very faint. The rings are made up of dust particles thought :0 have been made by tiny meteorites smashing into Neptune's moons. From ground based telescopes the rings appear to be arcs but from Voyager 2 the arcs turned out to be bright spots or clumps in the ring system. The exact cause of the bright clumps is unknown. The magnetic field of Neptune, like that of Uranus is highly tilted at 47 degrees from the rotation axis and offset at least 0,55 radii (about 13,500 kilometers or 8,500 miles) from the physical center. Comparing the magnetic fields of the two planets, scientists think the extreme orientation may be characteristic of flows in the interior of the planet and not the result of that planet's sideways orientation or of any possible field reversals at either of the planets.
Facts: Diameter: 30,760 mi. 21 Mass: 1024x10 kg Gravity: 33 ft/s 2 Distance from Sun: 4,504,000,000 mi. Length of Day: 16.11 hrs Length of Year: 164.8 years Mean Temp: -170o F Tilt of Axis: 28.31o Atm. Pressure: 1.4 atm. 85% Atmosphere: H2 He 13% NH4 2%
Mythology: Neptune was the Roman god of the sea. He had power over the sea and seafaring, causing or preventing ocean storms at will. Neptune resembled the Greek god Poseidon. Like Poseidon, Neptune was also the god of horses and earthquakes. Because of the importance of sea travel and trade in the Roman culture, Neptune was an important god. Romans prayed to Neptune for safe travel over the sea. Neptune was the son of Saturn and Ops.
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PLUTO A
Facts: Diameter: 1413 mi. 21 Mass: 12.7x10 kg 2 Gravity: 8 ft/s Distance from Sun: 5,913,000,000 mi. Length of Day: 6.4 days Length of Year: 248.54 years Mean Temp: -400o F Tilt of Axis: 122.5o Atm. Pressure: 0 atm. 98% Atmosphere: N 2 Other 2%
lthough Pluto was discovered in 1930, limited information on the distant planet delayed a realistic understanding of its characteristics. Today Pluto remains the only planet that has not been visited by a spacecraft, yet an increasing amount of information is unfolding about this peculiar planet. The uniqueness of Pluto's orbit, rotational relationship with its satellite, spin axis, and light variations all give the planet a certain appeal. Pluto is usually farther from the Sun than any of the mile planets', however, due to the eccentricity of its orbit, it is closer than Nopitinc for 20 years out of its 249 year orbit. Pluto crossed Neptune's orbit January 21. 1979. made its closest approach September 5, I 989. and will remain within the orbit ol Neptune until February II. 1999. This will not occur again until September 2226. As Pluto approaches perihelion it reaches its maximum distance from the eliptic due to its 17-degree inclination. Thus, it is far above or below the plane of Neptune's orbit. Under these conditions. Pluto and Neptune ill not collide and do not
Mythology: Pluto was the god of the dead in Roman mythology and was almost identical to Hades, the Greek god of the dead. The Roman people borrowed and preserved without change almost all the myths about Hades and his underworld kingdom, the unseen world. Some scholars believe the Romans had no god of the dead before they came into contact with the Greek culture in the 700's B.C. Pluto represents evolution and transformation.
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Pluto and Neptune will not collide and do not approach closer than 18 A.U. to one another. Pluto's rotation period is 6.387 days, the same as its satellite Charon. Although it is common for a satellite to travel in a snchronous orbit with its planet, Pluto is the only planet to rotate synchronously with the orbit of its satellite. Thus being tidally locked. Pluto and Charon continuously face each other as they travel through space. Unlike most planets, but similar to Uranus, Pluto rotates with its poles almost in its orbital plane. Pluto's rotational axis is tipped 122 degrees. When Pluto was first discovered, its
was first discovered, its relatively bright south polar region was the view seen from the Earth. Pluto appeared to grow dim as our viewpoint gradually shifted from nearly pole-on in 1951 to nearly equator-on in 1973. Pluto's equator is now the view seen front Earth. For five years, Earth was aligned with the orbit of Charon around Pluto such that an eclipse of Charon ni front of Pluto could be observed once every Pluto day.