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The Planets The Solar System in which we belong contains many varied worlds all with their different story to tell, in this document we will try and explore this worlds and bring some of there exotic features to you. The solar system has nine planets in, some might argue that the 9th – Pluto is not actually a planet but a Kuiper belt object, but we will assume that Pluto is a planet. The Solar System is 4.5 billion years old. It was initially a rotating gas cloud, as time passed gravity became the dominant force, hence began to contact and angular momentum was conserved. The cloud flattened and material drifted towards the centre forming a ‘protosun’. Temperature kept rising until fusion began. For the gas giants the most probable explanation to their formation is that gravitational instabilities lead to the collapse of gas left over form the creation of the Sun. The rocky planets probably formed by the planetisimal theory i.e. dust grains collide and merge together and gradually larger bodies associate together. The planets travel around the Sun in elliptical orbits, a fact first noticed by Johannes Kepler in 1609. An inferior planet is one which has an orbit that is inside that of the Earth and the others are sad to be superior. The inner solar system is defined as being: Mercury, Venus, Earth, Mars (asteroid belt) and the outer solar system is: Jupiter, Saturn, Uranus, Neptune and Pluto (which has a maximum distance from the sun of 7,375 million km. We shall start with the closest and work our way outwards, to the edge of the solar system and the Oort cloud. Mercury Orbit Diameter Mass Satellites Magnetic Field 57,910,000 km (0.38 AU) from Sun 4,880 km 3.30e23 kg None Approx 1% of the Earth’s Mercury is the closest planet to the Sun and also the eight largest. Mercury has been known of since at least the time of the Sumerians (about 3rd millennium BC). It was given two names by the Greeks: Apollo for its apparition as a morning star and Hermes as an evening star. Greek astronomers knew, however, that the two names referred to the same body. Some Greek astronomers even believed that Mercury and Venus orbited the Sun, not the Earth which is contrary to the popular belief at the time. In Greek mythology Hermes is the messenger of the Gods and the Roman counter part is Mercury; he god of commerce, travel and thievery. The planet probably received this name because it moves so quickly across the sky. Spacecraft: Mercury has been visited by only one spacecraft, Mariner 10. It flew by three times in 1974 and 1975. 45% of the surface was mapped. In more recent times it has been suggested that it should be mapped by the Hubble Space Telescope (HST), unfortunately, it is too close to the Sun to be safely imaged by HST. There are a few future missions to go back and map the rest of Mercury in the pipeline. The first is NASA’s Messenger (http://messenger.jhuapl.edu/index.html), which is due to be launched in 2004 and will start orbiting Mercury in 2004. The second is BepiColombo which is ESA’s first visit to the innermost planet, the objectives for this space craft are 1st dual Mercury orbiters, 1st Mercury lander, 1st European deep-space probe using electric propulsion. The point of Mercury's orbit closest to the Sun (perihelion) moves around the Sun faster than predicted by Newton's theory of gravity. The motion of Mercury remained a mystery until Albert Einstein overhauled the theory of gravity in 1915. BepiColombo will www.astrosoc.org.uk -2- The Planets measure Mercury's motion more accurately than ever before and thus provide one of the most rigorous tests ever of Einstein's theory. BepiColombo is named after Professor Giuseppe (Bepi) Colombo (1920-1984) from the University of Padua, Italy, a mathematician and engineer of astonishing imagination. He was the first to see that an unsuspected resonance is responsible for Mercury's habit of rotating on its axis three times for every two revolutions it makes around the Sun. Mercury's orbit is highly eccentric; at perihelion it is only 46 million km from the Sun but at aphelion it is 70 million. The perihelion of its orbit precesses around the Sun at a very slow rate. 19th century astronomers made very careful observations of Mercury's orbital parameters but could not adequately explain them using Newtonian mechanics. It was thought that another planet (sometimes called Vulcan) might exist in an orbit near Mercury's to account for the discrepancy. The real answer turned out that this discrepancy could only be accounted for when General Relativity is was applied to the system. Temperature variations on Mercury are the most extreme in the solar system ranging from 90 K to 700 K. The temperature on Venus is slightly hotter but very stable. Mercury is in many ways similar to the Moon: its surface is heavily cratered and very old; it has no plate tectonics. On the other hand, Mercury is much denser than the Moon (5.43 gm/cm3 vs 3.34). Mercury is the second densest major body in the solar system, after the Earth. Mercury's interior is dominated by a large iron core whose radius is 1800 to 1900 km. The silicate outer shell (analogous to Earth's mantle and crust) is only 500 to 600 km thick. At least some of the core is probably molten. Mercury actually has a very thin atmosphere consisting of atoms blasted off its surface by the solar wind. Because Mercury is so hot, these atoms quickly escape into space, so Mercury's atmosphere is constantly being replenished. One of the largest features on Mercury's surface is the Caloris Basin; it is about 1300 km in diameter. It is thought to be similar to the large basins (maria) on the Moon. Like the lunar basins, it was probably caused by a very large impact early in the history of the solar system. That impact was probably also responsible for the odd terrain on the exact opposite side of the planet. The plains of Mercury are relatively smooth, probably due to some ancient volcanic activity but possible due to the result of the deposition of ejecta from cratering impacts. There is even a suggestion of water ice in the protected shadows of some craters around the north pole of Mercury’s surface; this is from radar observations as this region was not mapped by Mariner 10. Venus Orbit Diameter Mass Satellites Magnetic Field 108,200,000 km (0.72 AU) from Sun 12,103.6 km 4.869e24 kg None Zero Venus is the second planet from the Sun and the sixth largest. Venus' orbit is the most nearly circular of that of any planet, with an eccentricity of less than 1%. Venus is the name of the Roman (Greek: Aphrodite; Babylonian: Ishtar) goddess of love and beauty The planet is so named probably because it is the brightest of all the planets known to the ancients. The majority of the surface features on Venus are named after female figures. Venus is usually visible with the unaided eye. Sometimes referred to as the ‘morning star’ or the ‘evening star’, it is by far the brightest ‘star’ in the sky. Venus has been known since prehistoric times. Except for the Sun and the Moon it is the brightest object in the sky. Like Mercury, it was popularly thought to be two separate bodies: Eosphorus as the morning star and Hesperus as the evening star, but the Greek astronomers of the time knew like they did with Mercury that the two bodies are the same object. www.astrosoc.org.uk -3- The Planets Venus is an inferior planet, which means when viewed from the perspective of the Earth it shows phases. This was first observed by Galileo and his observation of the phenomenon was important evidence in favour of Copernicus’s heliocentric theory of the solar system. Venus has a strange rotation, it is very slow (243 Earth days per Venus day, slightly longer than Venus' year) and retrograde. In addition, the periods of Venus' rotation and of its orbit are synchronized such that it always presents the same face toward Earth when the two planets are at their closest approach. Whether this is a resonance effect or merely a coincidence is not known. Spacecraft: In 1962 the first spacecraft visited Venus, this was Mariner 2. It has since been visited by more than 20, including Pioneer and the Soviet Venera 7 which was the first spacecraft tot land on another planet. Venera 9 was the first to return photographs of the surface (see right). To get a better picture of what is going on under the clouds of Venus the Magellan spacecraft mapped the surface of Venus using radar (see main image of Venus). Venus is sometimes regarded as Earth's sister planet. In some ways they are very similar. Venus is only slightly smaller than Earth (95% of Earth's diameter, 80% of Earth's mass). Both have few craters indicating relatively young surfaces. Their densities and chemical compositions are similar. Since Venus seems so similar to the Earth, it was thought that below its dense clouds Venus might be very Earthlike and even have life; however detailed study of Venus reveals that in many important ways it is quite drastically different from the Earth. The pressure of Venus' atmosphere at the surface is 90 atmospheres (about the same as the pressure at a depth of 1 km in Earth's oceans). It is composed mostly of carbon dioxide. There are several layers of clouds many kilometres thick composed of sulphuric acid. These clouds completely obscure our view of the surface. This dense atmosphere produces a run-away greenhouse effect that raises Venus' surface temperature by about 400 degrees to over 740 K (hot enough to melt lead). Venus' surface is actually hotter than Mercury's despite being nearly twice as far from the Sun. In the upper atmosphere there are strong winds (350kph) but at the surface they are very slow, no more than a few kilometres per hour. Venus' surface consists mostly of gently plains with little relief. There are also several broad depressions: Atalanta Planitia, Guinevere Planitia, Lavinia Planitia. There two large highland areas: Ishtar Terra in the northern hemisphere (about the size of Australia) and along the equator Aphrodite Terra (size of South America). The interior of Ishtar consists mainly of a high plateau, Lakshmi Planum, which is surrounded by the highest mountains on Venus including the enormous Maxwell Montes. Data from Magellan's imaging radar shows that much of the surface of Venus is covered by lava flows. Recently announced findings indicate that Venus is still volcanically active, but only in a few hot spots; it has been geologically rather quiet for the past few hundred million years. There are no small craters on Venus, the small meteoroids burn up in Venus' dense atmosphere. Craters on Venus seem to come in bunches indicating that large meteoroids that do reach the surface usually break up in the atmosphere. The interior of Venus is probably very similar to that of Earth: an iron core about 3000 km in radius, a molten rocky mantle comprising the majority of the planet. Like Earth, convection in the mantle produces stress on the surface which is relieved in many relatively small regions instead of being concentrated at plate boundaries as is the case on Earth. Earth Orbit Diameter Mass Satellites www.astrosoc.org.uk by definition, 1 AU, or 149.6 million km from Sun 12,756.3km 5.972^24 kg The Moon (Lunar) -4- The Planets Earth is the fifth-largest planet. Most of mass is in the layer called the mantle, and if you know any more geography than the author you’ll know what that is. Earth is the only planet on whose surface water can exist in liquid form. Obviously, it has just the one natural satellite, and all spacecraft have been there! The earth's magnetic field interacting with solar wind causes aurora borealis and australis, and also the magnetic field to move and occasionally reverse completely. The geomagnetic north pole is currently in northern Canada. Mars Orbit Diameter Mass Satellites Magnetic Field 227,940,000 km (1.52 AU) from Sun 6,794 km 6.4219e23 kg 2; Phobos and Diemos Weak This planet was not covered in the talk since this was covered in a specific talk already for more information please see the Mars document which currently can be found at: http://students.bugs.bham.ac.uk/astrosoc/educational/Mars.pdf Jupiter Orbit Diameter Mass Satellites Magnetic Field 778,330,000 km (5.20 AU) from Sun 142,984 km (equatorial) 1.900e27 kg about 40 Huge magnetic field Jupiter is the largest planet in our Solar system, being over 1000 times greater in volume and 300 times greater in mass than the Earth. It is the Earth’s saviour; asteroids that would be extinction level events (ELEs) if they impacted the Earth have instead been swallowed up by the giant planet. This is probably partly why life was able to develop as it is on Earth. It is composed mainly of Hydrogen and Helium. Through a good telescope it appears as yellowish dish crossed by dark streaks which are known as the ‘cloud belts’. The most stable of the bright bands have been named. Like all the other giant planets it spins very quickly causing an equatorial bulge producing a shape which is described as oblate. The most famous feature on its surface is the Great Red spot, which is know to have persisted for over 300 years. It is not stationary and drifts over time. It is roughly 3 times greater than the radius of the Earth. There are many theories as to its origin but one of the most promising is a ‘solitary wave’ which is an isolative permanent wave which can flow between tow layers of a fluid when there is a velocity difference between the layers. The wave takes its energy from the velocity gradient. The temperature of Jupiter is between 104 and 105 K. Spacecraft: Pioneer 10 1972, Pioneer 11 1974, Voyager 1 1977, Voyager 2 1977 Satellites: There are currently 40 known moons around Jupiter. The four most famous and the largest are the Galilean moons; Io, Europa, Ganymede and Callisto (in order of distance from Jupiter, can be memorised via ‘I Eat Green Cheese’). These moons are so large that they are comparable to the smaller www.astrosoc.org.uk -5- The Planets planets such as Mercury and are found on an almost circular orbit in Jupiter’s equatorial plane. They are called Galilean as they were first discovered by Galileo in 1610. Io It is the most dense of the Galilean satellites been about as dense as the moon (3.5×103 kgm-3). As the closest moon it is subject to a strong gravitational attraction from Jupiter on the one side and on the other that of the rest of the Galilean satellites. This causes its surface to flex and the resulting friction produces heat to cause a molten interior. Europa The smallest Galilean moon. Its very high albedo (reflectivity) suggests that it has an icy surface. There are very few craters on its surface which suggests that it may have remained in a slushy state until the main bombardment era was over. It suffers from similar gravitational force as Io (only 10% of the strength that Io receives) which may have lead to a water or slushy region beneath the surface which many people postulate that there may be life there. Ganymede It is the largest and brightest Galilean satellite. The overall density is less that that of water there it is inferred that if consists of around ½ rock and ½ ice. It is believed that there may be a convective mantle or water below the 100km thin crust. Callisto The least dense of the Galilean moons being one of the lowest satellite densities measured. Also has a low albedo and so appears much fainter than tits companions. It is thought to have a thin crust 200 to 300 km thick below which there is a convection layer or water or soft ice, similar to that of Ganymede. Its surface is saturated with craters and is thought to be approximately 4000 million years old, this makes it the oldest landscape surfaces in the whole solar system. Saturn Orbit Diameter Mass Satellites Magnetic Field 429,400,000 km (9.54 AU) from Sun 120,536 km (equatorial) 5.68e26 kg 30 named Significant Saturn is the sixth planet from the Sun and the second largest. In Roman mythology, Saturn is the god of agriculture. In Greek mythology Saturn was the god, Cronus, who was the son of Uranus and Gaia and the father of Zeus (Jupiter). Saturn is the root of the English word ‘Saturday’. Saturn has been known of since prehistoric times. In 1610 Galileo was the first to observe it with a telescope; he was confused by its rather odd. It seems that early observations of Saturn were complicated by the fact that the Earth passes through the plane of Saturn's rings every few years as Saturn moves in its orbit. This means that a low resolution image of Saturn will change drastically. It took another 50 years after Galileo first observed Saturn for Christian Huygens (in 1659) correctly inferred the geometry of the rings. Saturn was believed to be the only planet with rings until in 1977 when faint rings were discovered around Uranus and then shortly afterwards around Jupiter and Neptune. www.astrosoc.org.uk -6- The Planets Saturn was first visited by Pioneer 11 in 1979 and later by Voyager 1 and Voyager 2. Cassini, now on its way, will arrive in 2004. Saturn is visibly flattened (oblate) when viewed through a small telescope; its equatorial and polar diameters vary by almost 10% (120,536 km vs. 108,728 km). This is the result of its rapid rotation (differential rotation) and fluid state. The other gas planets are also oblate, but not so much so. Saturn is the least dense of the planets; its specific gravity (0.7) is less than that of water. Like Jupiter, Saturn is about 75% hydrogen and 25% helium with traces of water, methane, ammonia and "rock", similar to the composition of the primordial Solar Nebula from which the solar system was formed. Saturn's consists of a rocky core, a liquid metallic hydrogen layer and a molecular hydrogen layer; this is similar to that of Jupiter. Traces of various ices are also present. Saturn's interior is hot (12000 K at the core) and Saturn radiates more energy into space than it receives from the Sun. Most of the extra energy is generated by the Kelvin-Helmholtz mechanism, the slow gravitational compression of the planet, as in Jupiter. But this may not be sufficient to explain Saturn's luminosity; some additional mechanism may be at work, perhaps the ‘raining out’ of helium deep in Saturn's interior. Saturn has bands in the atmosphere, like Jupiter but in the case of Saturn they are much wider near the equator and far fainter. Most of the details are not visible from the Earth so it was not until the Voyages encounters that any detail of Saturn’s atmospheric circulation could be studied. Saturn also exhibits long-lived ovals (e.g. Red Spot on Jupiter). In 1990, the Hubble Space Telescope (HST) observed an enormous white cloud near Saturn's equator which was not present during the Voyager encounters. From the Earth two prominent rings (A and B) and one faint ring (C) can be seen. The gap between the A and B rings is known as the Cassini division. The fainter gap in the outer part of the A ring is known as the Encke Division (but this was very likely never seen by Encke). The Voyager pictures show four additional faint rings. Saturn's rings are extraordinarily thin, only about one kilometre thick. Voyager confirmed the existence of puzzling radial inhomogeneities in the rings called ‘spokes’ which were first reported by amateur astronomers. The nature of these ‘spokes’ remains a mystery, but may have something to do with Saturn's magnetic field. There are complex tidal resonances between some of Saturn's moons and the ring system. Some of the moons, such as the ‘shepherding satellites (e.g. Atlas, Prometheus and Pandora) are important in keeping the rings in place. Mimas seems to be responsible for the paucity of material in the Cassini division. Saturn's Satellites Saturn has 30 named satellites plus one discovered in 2003 and as yet unnamed. Of these Titan is the largest. Titan Titan is the fifteenth of Saturn's known satellites and the largest: In Greek mythology the Titans were a family of giants, the children of Uranus and Gaia, who sought to rule the heavens but were overthrown and supplanted by the family of Zeus. Titan was discovered by Huygens in 1655. It was long thought that Titan was the largest satellite in the solar system but recent observations have shown that Titan's atmosphere is so thick that its solid surface is slightly smaller than Ganymede's. Titan is nevertheless larger in diameter than Mercury and larger and more massive than Pluto. Alone of all the satellites in the solar system, Titan has a significant atmosphere. At the surface, its pressure is more than 1.5 bar. It is composed primarily of molecular nitrogen with 6% argon and a few percent methane. There are also trace amounts of other organic compounds (e.g. ethane, hydrogen www.astrosoc.org.uk -7- The Planets cyanide, carbon dioxide) and water. In many ways, this is similar to the conditions on Earth early in its history when life was first getting started. It seems likely that the ethane clouds would produce a rain of liquid ethane onto the surface perhaps producing an "ocean" of ethane (or an ethane/methane mixture) up to 1000 meters deep. Uranus Orbit 2,870,990,000 km (19.218 AU) from Sun Diameter Mass Satellites Magnetic Field 51,118 km 8.683^25 kg 27 named Unusual (see below) Uranus is the first planet whose discovery is recorded, i.e. the first planet discovered which, while visible with the naked eye, is too insignificant to have been noticed. Although the Hindus believed in nine planets, they thought one was the Sun and the two they could not see were "nodes" of the motion of the Moon, and there is no evidence that they knew of Uranus, Neptune or Pluto. Uranus was discovered by William Herschel, on March 13, 1781. It had been seen before but mistaken for a star. The earliest recorded sighting was by John Flamsteed, who called it 34 Tauri in 1690. Herschel named it “the Georgian planet” in honor of George III, others named it after the discoverer. Bode proposed the name Uranus, and it was in common use by 1850. Uranus was visited by Voyager 2 on January 24 1986. The axis of Uranus’ rotation is almost parallel to the plane of its rotation, oddly, so the polar regions receive more light. However, by an unknown mechanism, the equatorial regions remain hotter. The magnetic field unusual in that it is at 60 degrees to the axis of rotation. There is some disagreement as to which of Uranus’ poles is its north! Uranus is composed of rock and ices, and its atmosphere is about 83% hydrogen, 15% helium and 2% methane. The methane is concentrated in the upper atmosphere, giving the planet its blue colour. All of the named moons in the solar system are named after characters (e.g., assorted nymphs) or types of being (e.g. Neptune’s Nereid, named after a type of nymph, not an individual) from Greco-Roman mythology with the exception of the Earth’s and Uranus’ moons. The Earth’s moon is not named after anything, and Uranus’ moons, unusually, have been named from the writings of Shakespeare and Pope. You will be disappointed to learn that Uranus has as yet no moon named Bottom. Uranus has 11 rings, and 27 known satellites, as follows: Cordelia, Ophelia, Bianca, Cressida, Desdemona, Juliet, Portia, Rosalind, Belinda, Puck, Miranda, Ariel, Umbriel, Titania, Oberon, Caliban, Stephano, Trinculo, Sycorax, Prospero, and Setebos. www.astrosoc.org.uk -8- The Planets Neptune Orbit Diameter Mass Satellites Magnetic Field 4,504,000,000 km (30.06 au) from the Sun 49,532 km 1.0247^26 kg 13 Unusual (see below) Neptune is also visible with the naked eye, but insignificant. Pluto's eccentric orbit means that sometimes Neptune is the furthest from the sun. After discovery of Uranus, something was noticed to be disturbing its orbit. Adams and Le Verrier predicted its location and it was found very near there by Galle and D'Arrest on 24 September 1846. The English and the French squabbled over discovery rights and are now jointly credited. The original predicted orbit diverges quickly from actual orbit, so it was lucky that they observed the planet before it moved from near the predicted orbit. It was nearly discovered over 200 years earlier by Galileo in 1613, but he mistook it for a star. In fact, he did notice a small movement on two successive nights, but on following nights the weather was bad and he was prevented from following its motion. Had it not been cloudy he would probably have identified it as a planet. Neptune was visited by Voyager 2 on August 25 1989. A dark spot was observed, about twice the size of Earth and probably a storm like the spot on Jupiter. However subsequent HST observations have failed to locate it. The planet is similar in composition to Uranus. The blue colour is also from methane, but some other unknown chemical makes the clouds a particularly rich hue. Neptune has the fastest winds in the solar system at up to 2000 km/hour (no Uranus jokes please!). It radiates twice as much energy as it gets from the Sun. Like Uranus, it has rings and an oddly oriented magnetic field generated by motions of conductive material (probably water) in its middle layers One ring has a twisted structure. Neptune has 13 known satellites: Naiad, Thalassa, Despina, Galatea, Larissa, Proteus, Triton, and Nereid, plus 5 unnamed ones. Pluto Orbit Diameter Mass Satellites 5,913,520,000 km (39.5 AU) from the Sun (average) 2,274 km 1.27e22 kg 1; Charon After the discovery of Neptune in 1846 there were still slight perturbations in the movements of the outer planets. During 1930 Clyde Tombaugh used a blink-microscope and took photos on two different nights and compared them, the stars would remain in the same relative positions but a planet would shift during the interval and its motion would be revealed. The planet was named Pluto after the God of the underworld and Darkness, as suitable name for the most remote planets in the solar system. Pluto is smaller than the moon and has one satellite called Charon which is around half the size of Pluto, hence it is often said that they may be a double planet or even a double asteroid. Pluto has a very eccentric orbit which when Pluto is at perihelion it is closer to the Sun than Neptune. Pluto does have a tenuous atmosphere of methane, but this may be a cyclic phenomenon so that when Pluto moves towards aphelion the temperature may fall and the methane may condense onto the surface. It has an orbit of 124 years. www.astrosoc.org.uk -9- The Planets Mythology Here we examine what amounts to being the history of astronomy. In ancient times there was a lot that people didn’t understand, and most of it was attributed to the supernatural or the divine. While today we know that Venus is just a lump of rock with a sulphurous atmosphere, the Mayans thought it was a bringer of war that should be feared intensely, and the Greeks thought it was the celestial avatar of love itself. With the exception of Earth, all of our planets are named after Roman gods. Roman mythology, in fact, is almost exclusively Greek, although they took over some Celtic lore where they found it (here in Britain there are many ruined Roman buildings dedicated to indigenous deities whom the Romans had incorporated into their belief system). The Romans were fascinated by the Greeks and basically took up all of the ancient Greek religion. Where possible they assimilated the Greek gods to gods of their own invention, which is why many Roman divinities have two names: the original Greek name and the name of the Roman god whom the Romans felt best fitted the attributes of the Greek god they wanted to make their own. Where possible we will speak of old Roman mythology, but in many cases there is bugger-all information on Roman beliefs independent of ancient Greek religion. To further add to the confusion, Greek mythology drew influence itself from Mesopotamian mythology (the ancient region of Mesopotamia corresponds approximately to modern-day Iraq and Kuwait). Mercury Mercury (or Alipes) was the Roman god of commerce, and was originally the god of the corn trade. The Germans identified him with their god Wodan, and the Celts with Lugh. He was later equated with the Greeks’ Hermes, who was the messenger of the gods, and the god of travel and trade. The Greeks called the planet Apollo (after Hermes’ brother) in the morning but were aware that it was the same planet. In fact, Heraclitus even proposed that it and Venus orbited the sun. The planet was probably named Mercury because it moves rapidly across the sky, and messengers have to be quick. The Hindus associated the planet with the god Budha. Venus Venus was the Roman goddess of vegetation, who later became the goddess of love and beauty and was eventually assimilated with the Greek goddess of love Aphrodite. Aphrodite was born from the splash created when Cronus threw his father’s severed genitals into the sea. Baffled? We’ll get to that later. Aphrodite, in folkloric terms, was related to the Mesopotamian goddess Ishtar and the Etruscan goddess Turan. From Aphrodite we get the word ‘aphrodisiac’ and from Venus the term ‘venereal disease’ (i.e. a disease of love). When it appeared in the morning, the Romans named the planet Lucifer, meaning “light-bearer.” The Hindus associated the planet with a god called Sukra, who knew the secret to bringing the dead back to life. In pre-Islamic times in the Middle East God was believed to have daughters, one of whom, a goddess called Uzza, was associated with Venus. In Latvian mythology (yes, Latvian), the planet Venus was associated with a god called Auseklis, who may at some point have been a goddess. He was going to marry the Sun’s daughter, but she ran off with the Moon! Old German stories tell of a diminutive and kindly people called the Venusleute (people of Venus), who aided lost children. In Aztec mythology, a god called Tlahuizcalpantecuhti was associated with Venus when it appeared in the morning, and believed to be an incarnation of a feathered serpent called Quetzalcoatl. The Aztecs and Toltecs associated it with a god called Xolotl when it appeared in the evening. He was believed to be a dog-headed man or a skeleton. The Incas identified the planet with a virgin goddess Chasca. The Mayans called the planet Kukulcan, associated it with warfare and feared it to the point where they www.astrosoc.org.uk - 10 - The Planets blocked up their chimneys to prevent its light entering their houses! When Venus appeared above the crescent moon, the Sumu Indians said that it was the wife of Udo, the god of the Moon. In Polynesia Venus was called Malara in the morning. Malara was believed to be seeking wives. It is said that the Maori people sailed from Polynesia to their current home of New Zealand, guided by the planet Venus. Earth Earth is the only planet not named after a Roman god. Its name is Old English/Germanic. The Moon is also not named after a god, and being such an important object in the sky its mythology is so extensive that it deserves to be left for a different article. The Greeks associated the Earth with a goddess called Gaia (whom the Romans equated with their goddess Tellus). She came out of Chaos and created everything. The ancient Egyptians believed the Earth was a god called Geb, Keb or Seb, the provider of crops and healer of ailments. In a sadistic twist, his laughter caused earthquakes. He was a green- or blackskinned bearded man with a goose on his head! Another Egyptian Earth god was Tatenen, who represented the first sign of Earth appearing from the primordial waters. He also had green skin, as well as a crown of feathers and ram’s horns. The Aztecs associated the Earth with a goddess called Coatlicue, meaning "serpent skirt", who was the goddess of life and death, wore a skirt made of serpents (duh) and a necklace of hearts and wanted regular human sacrifices. The moon was the head of a daughter who tried to kill her, which Coatlicue bit off and spat out. There was also an earth and cave god, Tepeyollotl, associated with the jaguar, who caused earthquakes and echoes. The Inca Earth goddess was the generous Pachamama, wife of the Sun god. The Yuncas had an Earth god called Pachacamac, whose wife was Mama Pacha. The Incas adopted him, presumably explaining the origins of Pachamama. Another Inca Earth goddess, or perhaps another name for the aforementioned, was Mama Allpa, who had many breasts! In Norse mythology the Earth was called Midgard, and was the body of a giant called Ymir killed by the god Odin and his brothers Vili and Ve. The goddess of the Earth was Gerd. Slavic lore told of an Earth goddess called Mokos, who may have been an evolution of an older goddess called “Damp Mother Earth,” Mati Syra Zemlya. In what is now Eastern Europe many similar Earth goddesses were worshipped, probably derived from an old Indo-Iranian goddess called “Humid Mother of the Earth,” Ardvi Sura Anahita. In Russia, Mokos may live on unofficially in Orthodox Christianity in the form of Saint Paraskeva-Piatnitsa. In old Islamic folklore, the earth was said to be held in the horns of a giant bull, which stands on the head of a big fish called Labuna! Angels bring food for the fish every day, but the author has been unable to discover what the bull was supposed to eat. The Japanese had/have an Earth god called Kenro-Ji-Jin, meaning “Solid Earth Being.” There was also a god called Sarudahiko who had a red face, round eyes, and a long, phallic nose. Most Earth deities are associated with fertility in some way, for obvious reasons, and most seem to be female. At this point the author is going to resort to simply listing Earth deities about which there is little to say or little (interesting) information available: Zemepates and Zemyna – Lithuanian god and his goddess sister Hwanin – Korean god, also god of Heaven, sent his son to Earth to found a city near modern-day Pyongyang Armaiti – Persian goddess, also associated with the dead because they are buried underground Erda – ancient German goddess Chibirias – Mayan goddess Colel Cab – Mayan goddess Etugan – Mongol virgin goddess Audial – goddess from Caroline Islands www.astrosoc.org.uk - 11 - The Planets Zempat – Prussian god, also god of cattle Eseasar – African goddess Altan-Telgey – Mongol god Enlil – Sumerian, also god of the air Papa – Maori goddess, a.k.a. Fakahotu Awitelin Tsta – goddess of the native American Pueblo Zeni tribe Hou Ji – Chinese, also god of cereal crops Anatu – Mesopotamian goddess, also queen of the sky Jian Lao – Chinese god, also god of permanence Tanen – Egyptian, the god Ptah in his ‘Earth god’ aspect Onamuji – Japanese god Itchita – Yakut goddess who lives in a beech tree and prevents illness Atugan - Mongol Nokomis – Algonquin goddess, ‘grandmother’ Prisni – Hindu goddess, also goddess of darkness Humban – Elamite god Ninhursag – Sumerian goddess, ‘queen of the mountain’ Mars Mars, a.k.a. Ultor and Mavors, began as a Roman god of fertility and growth, later becoming a chthonic (meaning of, or in the earth) god. Some earth gods became associated with death because the dead are buried in the ground, and this happened to Mars. From here we can see how he finally became associated with warfare, and was then associated with the Greeks’ Ares. Ares was one of two wardeities in Greek mythology, the other being Athena. However Athena was interested solely in upholding justice, where as Ares simply enjoyed bloodshed. Ares was accompanied by his sister Eris (Roman: Discordia), goddess of strife, an older war goddess called Enyo, and his sons Phobos and Deimos, ‘panic’ and ‘fear’, after whom the planet’s two moons are named. Mars was also associated with Cariocienus, an old Hispanic god, and Camulus, Teutates and BelatuCadros, Celtic gods. Mars was the father of the legendary wolf-nursed founders of Rome, Romulus and Remus. From the god Mars we get the name of the month of March. Many cultures associate the planet Mars with war, because it is red, like blood. The Hindus named the planet Mangala, and associated it with the god Karttikeya. He was created from six babies born from six sparks from the eyes of the god Shiva. The babies were nursed by the Pleiades. Shiva’s wife Parvati hugged the babies so hard that they stuck together into a single god, Karttikeya, who had 12 arms and 6 heads, was the god of war and rode a peacock! The Babylonian god of Mars was Salbatanu. The Mayans depicted Mars as a serpent snaking across the sky, possibly referring to its motion throughout the year. Jupiter Jupiter (a.k.a. Jove, Stator, and about a million other things) may be no more than a Romanised name for Zeus, Greek king of the gods and god of lightening and light. The planet may be named after him because it's a very bright object in the sky. Jupiter was associated with Jessis, a Slavic god, Hadad, a Syrian god, Tinia, an Etruscan god, and Taranaich and Bussumarus, Celtic gods. His hobbies were cheating on his wife (in fact he ate his first wife!) and creating innovative ways to avoid getting caught (e.g., changing himself and his target into animals). Jupiter’s moons are named after nymphs (beautiful female semi-divine beings from whom we derive the term ‘nymphomania’) with whom he had sex. Gods associated with Jupiter: Jessis – Slavic Hadad – Syrian Tinia – Etruscan Taranaich – Celtic Bussumarus – Celtic Thor – Norse www.astrosoc.org.uk - 12 - The Planets Donar - Teutonic In Judaic lore, Zadkiel is the angel of the planet Jupiter. The planet was associated by the Sumerians with their fertility god Sulpa’e. The Hindus had a god of Jupiter called Devapurohita, or Brivaspati. The name of the Chinese god Tai-Sui-Xing, “Star of the Big Year,” refers to Jupiter, with its twelveyear orbit. From the god Jupiter’s other name, Jove, we get the term ‘jovial’, as Zeus was supposed to be a jolly fellow. From Thor we get the name of the day of the week Thursday. Saturn Saturn was the Roman god of agriculture and particularly corn. He was associated with the Phoenician fertility god Baal-Hammon. He was equated with the Greek Cronus, who was the bringer of old age and god of agriculture. Cronus was always shown carrying a sickle, the instrument with which he carried out the harvest but also castrated his father. As such he was perhaps very much a god of regeneration – only when the old has been disposed of can we bring in the new. After castrating his father Uranus, Cronus succeeded him as king of the gods. Unfortunately his own behavior left him with a paranoia that his children would depose him, and hence he would eat all of his children as soon as they were born. However in the case of Zeus his wife (who was also his sister) tricked him into swallowing a rock instead, and his paranoia turned out to be justified when Zeus did indeed stage a coup and seize power. If you are wondering how a rock could be mistaken for a newborn child, don’t ask us because we don’t know. From the god Saturn we get the name of the day Saturday. The Hindu god of the planet Saturn was Sani, known as 'the evil-eyed one' because his gaze could burn. The following three planets have no real history, as they are fairly modern discoveries. However we shall briefly discuss the mythology behind their names. Uranus Uranus is a purely Greek god – the Romans equated him with their god Coelus, but for some reason we still use the Greek term. Uranus was the god of the sky, created by the Earth Mother goddess Gaia as a husband after she appeared alone out of the primordial Chaos. Uranus impregnated his wife, and did not ‘withdraw’ himself for so long that his children grew adult inside their mother, unable to be born. In order to allow them exit, one of the children, Cronus, cut off his father’s penis with a sickle his mother had given him. Having been emasculated, Uranus the Sky separated from Gaia the Earth. Uranus is a sky-blue planet, and the author stipulates that the planet may have been named after the sky god for this reason. Neptune Neptune was the Roman god of the sea, who may have evolved from the Etruscan water-god Nethuns. He became assimilated with the Greek god Poseidon. Poseidon was the god of the sea and the bringer of earthquakes. He was bad-tempered, a womanizer and a rapist. He even had sex with the Gorgon Medusa, famous for her snake-hair and lethal gaze (Poseidon being immortal had no need to fear this), from which union was produced the flying horse Pegasus. Neptune’s moons are named after random mythological characters and beings. Neptune was probably suggested as a name for this planet because it is blue, like the sea. Pluto The Roman Pluto, the Etruscan Aita and the Greek Hades are essentially identical. Hades was the god of the underworld, where the dead reside. Even the other gods avoided him. The ancients didn’t like to speak of him for fear of attracting his attention. His pet dog Cerberus had three heads. Pluto’s moon, Charon, is named after the immortal who ferried the newly dead and occasional visitors such as Hercules/Heracles and Orpheus across the river Acheron which separated the kingdoms of life and www.astrosoc.org.uk - 13 - The Planets death. The planet may be named after Pluto not only because it is a horrible icy rock, but also because the first two letters are the initials of Percival Lowell, the namesake of the observatory at which the planet was discovered. Images Cover Image: http://codep.ucsc.edu/planets.gif Messenger Spacecraft: http://messenger.jhuapl.edu/the_mission/artistimpression/images/orbitwithplanet.jpg Mercury: http://www.jb.man.ac.uk/public/mercury.gif Caloris Basin: starchild.gsfc.nasa.gov/ .../mercury_know.html Venus: http://www.solarviews.com/browse/venus/venus1.jpg Saturn: http://www.solarviews.com/eng/saturn.htm Uranus: http://www.solarviews.com/browse/uranus/uranus.jpg Uranus Atmosphere: http://hubblesite.org/newscenter/newsdesk/archive/releases/1996/15/ Uranus Satellites: http://www.lpi.usra.edu/research/outerp/usat.gif Earth: http://seds.lpl.arizona.edu/nineplanets/nineplanets/gif/Earthbig.jpg Jupiter: http://www.star.le.ac.uk/edu/planets/jupiter.gif Europa: http://seds.lpl.arizona.edu/nineplanets/nineplanets/europa.html Ganymede: http://www.solarviews.com/raw/jup/ganymede.gif Callisto: http://pds.jpl.nasa.gov/planets/captions/jupiter/callval.htm Io: http://www.jpl.nasa.gov/galileo/ganymede/P47971_full.jpg Mars: http://oposite.stsci.edu/ftp/pubinfo/jpeg/Mars95.jpg Neptune: http://pds.jpl.nasa.gov/planets/images/full/neptune/fullnep.jpg Neptune Spot: http://pds.jpl.nasa.gov/planets/jpeg/nep/gdspot2.jpg Pluto: http://www.seds.org/nineplanets/nineplanets/pluto.html Contributors: Samuel George Scott Porter Alexandra Yannacopoulou www.astrosoc.org.uk - 14 - The Planets