Guide to the Solar System

GUIDE TO THE SOLAR SYSTEM Solar System The Sun and Inner Planets The Sun makes up about 99.8% of the mass in the solar system. This means that almost the entire mass of the solar system is in the Sun. S UN F ACTS Diameter: 864,000 miles across (109 times the Earth’s diameter) Surface Temperature: 9980° Fahrenheit (F) Core Temperature: 27,000,000° F Duration of Rotation (Solar day): 27 to 31 days Composition: Made up mostly of hydrogen (70%) and helium (28%) and other (2%) Important spacecrafts: Solar Dynamics Observatory (SDO), Solar and Heliospheric Observatory, Solar Terrestrial Relations Observatory (STEREO), and many others. Also known as: Sol The Sun 2 The Sun is a Yellow Dwarf Star The Sun is the center of our solar system; all the planets in our system orbit around the Sun near the Earth’s orbital plane. 1,200,000 Earths can fit into the Sun. The Sun outshines about 80% of the stars in the Milky Way. However, there are many stars that are much bigger and brighter than our Sun. Our Sun is a mere runt compared to the biggest of these. The Sun is a G type star and takes about 225 million years to make one orbit around the Milky Way. It is known as a yellow dwarf, although its color is actually more white than yellow. It generates energy through nuclear fusion in its core. The Sun is located in the Orion arm of the Milky Way. Sunspots are areas of strong magnetic activity and lower temperature on the surface of the Sun. Some Sunspots are larger than the Earth, but Sunspots are not always present on the Sun. A solar wind is ejected from the Sun. It is made up of plasma – high energy protons and electrons that can escape the great gravity of the Sun. The solar wind is responsible for the northern and southern lights. We depend on the Sun for life. It is our source for life’s key ingredients: warmth and light. The dark marks on the surface are sunspots. Giant flares and prominences often erupt from the surface. The Snow Solar Telescope on Mt. Wilson in Pasadena, California, was one of the first telescopes designed to seriously study and understand the Sun. The telescope was moved from Wisconsin to Pasadena in 1904 and is still in operation today. 3 M ERCURY C LOSEST TO THE S UN Moons: None. Distance from Sun: 36 million miles (35,983,035 miles) or 0.39 AU (see page 8 to learn more about AUs) Diameter: 3031 miles (0.38 Earth’s diameter) Temperature range: 300 below 0° F (side facing away from Sun) to 700 above 0° F (side facing Sun) Duration of orbit around Sun (Mercurian year): 88 days Duration of Rotation (Mercurian day): 58.65 Earth days Important spacecraft: Mariner 10, Messenger Also known as: Hermes and Apollo (Greek), Chen Xing (⾠辰星) the Hour Star (ancient Chinese), Nabu (Babylonian) Mercury 4 Mercury is the smallest planet. The Greeks believed Mercury was two different planets. They called Mercury Apollo when it appeared in the morning and Hermes when it appeared at night. Mercury is a Roman name. Mercury moves very quickly around the Sun, so it was named after a fast moving Roman god. Ice was discovered in a crater at its north pole by the Messenger spacecraft. Mercury is a rocky planet composed mostly of silica and an iron core. Silica is the material that is found in sand, cement, crystals and quartz. Mercury has no atmosphere. It once had volcanic activity and its plains deformed as the planet cooled. It is the smallest planet in the solar system— smaller than Jupiter’s moon Ganymede and Saturn’s moon Titan. The Messenger spacecraft discovered that Mercury has shrunk about 8 miles over the centuries. This image uses false color to bring out Mercury’s features; it’s actual color is dark gray. 5 V ENUS THE M YSTERIOUS Moons: None. Distance from Sun: 67 million miles (67,237,981 miles) or 0.72 AU Diameter: 7521 miles (just slightly smaller than Earth) Temperature: constant 800° F Duration of orbit around Sun (Venusian year): 224 Earth days Duration of Rotation (Venusian day): 243 Earth days Significant spacecrafts: Venera (Russia), Pioneer, Mariner and Magellan (USA), Venus Express (ESA) Also known as: The morning star, the evening star. Greeks called it Phosphorus when it was visible in the morning and Hesperus when it was visible in the evening. Romans called it Lucifer (morning) and Vesper (evening). Venus 6 Venus is just slightly smaller than the Earth. The Greeks and Romans believed Venus to be two different planets. They called Venus Phosphorus or Lucifer when it appeared in the morning and Hesperus or Vesper when it appeared at night. Venus is rocky planet covered with lava from ancient volcanic eruptions (and possibly more recent eruptions, too) and has has flattened volcanos called farra. The atmosphere is primarily made of carbon dioxide and has thick clouds in the atmosphere made up of sulphuric acid. The clouds create a “greenhouse effect” – a blanketing effect that holds onto heat. Venus has a temperature of 800° F and is even hotter than Mercury. Lightning has been detected on Venus. Russia’s Venera 9 took the first photos of the planet’s surface. Several spacecraft that entered Venusian atmosphere were crushed by its extreme pressure. The Magellan probe mapped the surface of Venus with radar as optical photos are difficult, if not impossible, due to the dense clouds. Venus passing in front of the Sun (known as a transit). As Venus has a size similar to Earth’s, this image gives an idea of how small the Earth might look next to the Sun. Tr a n s i t s o f M e r c u r y a n d Ve n u s Venus and Mercury are the only two planets in our solar system we can see pass in front of the Sun, because they are closer to the Sun than the earth. When we see a planet pass in front of a Sun or an exoplanet pass in front of a distant star, we call this event a transit. 7 Factoids What is the Ecliptic? It is the Earth’s orbital plane. All the major planets in the solar system follow the path of the ecliptic. From our point of view on Earth, this makes it seem like the Sun, Moon and planets cross the sky along the same, general path. What is an AU? In olden days, people thought this path was special and created 12 pictures made up of the stars along this path. They called these pictures the Zodiac - just another word for zoo, as most of the pictures were of animals. Of course, these days, we call celestial pictures of stars constellations. An AU or astronomical unit is the distance from the Sun to the Earth. So the distance from the Sun to the Earth is 1 AU. Mercury and Venus are closer to the Sun, so their distance is less than 1 AU. Neptune is about thirty times the distance from the Sun as the Earth, so it is 30 AUs from the Sun. One Light year equals 60,000 AUs. 8 E ARTH H OME S WEET H OME Moons: One. Distance from Sun: 93 million miles (92,956,021 miles) or 1 AU Diameter: 7918 miles Temperature range: -130° F to 132° F Duration of orbit around Sun (Earth year): 365.26 days (365d 6hr 9min) Duration of Rotation (Earth day): 24 hours First spacecraft to orbit Earth: Sputnik 1 (Russia, 1957) Also known as: Terra, Gaia, the big blue marble Earth 9 The Moon is our companion as we orbit the Sun Earth’s molten core provides a magnetic field that protects the planet from harmful solar radiation. Mercury, Venus and Mars do not have this protection. The deflection of solar radiation sometimes results in colorful displays known as auroras or the northern and southern lights. Earth is only planet currently known to harbor life. Some life forms, such as whales, humans, elephants and dolphins, exhibit intelligence. One out of every four life forms on Earth is a beetle, and nine out of ten are insects. Earth’s atmosphere is composed mainly of nitrogen and oxygen. Lightning can be observed on Earth as well as wind, rain, snow, and a variety of cloud types and dust storms. Most of the surface features on Earth have been formed by the movement of water and ice, and tectonic plates. Geysers are sometimes found near volcanic vents. The gravity of the Moon affects the ocean tides on Earth and is slowing down the rotation of our planet ever so slightly. The Earth once rotated once every six hours and the Moon has now slowed down our rotation to once every 24 hours. The Earth continues to slow down! Galileo thought the Moon was covered with seas. He called them mare, the Latin word for seas. We now know this material is lava, created by asteroid and cometary impacts that pierced the crust of the ancient Moon and ejected its hot interior onto the surface. The Moon is about one-sixth the size of Earth. We can only see one face of the Moon due to its rotation. It has mountains, craters (about 40 filled with ice) and molten material called mare. When the Moon passes in a certain position between the Earth and Sun, the Moon blocks the Sun’s light and a solar eclipse occurs. 10 M ARS THE R ED P LANET Moons: Two, Phobos and Deimos Distance from Sun: Varies, averaging 142 million miles or between 1.3 and 1.6 AU Diameter: 4221 miles (about one-half the size of Earth) Temperature range: 225 below 0° to 90° above F Duration of Orbit (Martian year): 2.14 Earth years (687 days) Duration of Rotation (Martian day): 1.03 Earth days (24 hrs 37min), just slightly longer than an Earth day. A martian day is known as a “Sol.” Significant spacecrafts: Spirit, Opportunity, Curiosity (rovers), Phoenix, Viking, Pathfinder, Mars Express. Also known as: Ares, the Roman god of war, Fire Star" (⽕火星) in Asian cultures Mars 11 Mars as viewed by the Hubble Space Telescope Mars is a rocky planet with plains, impact craters and caves. It was once believed to have canals on its surface, but this was an illusion produced by early telescopes. Dust storms, dust devils and tornados have been observed. Water Ice was discovered underground and tested by the Phoenix spacecraft. The Opportunity, Spirit and Curiosity rovers also discovered evidence that water once flowed on Mars. The poles of Mars have ice caps made up of layers of water ice and dry ice, one to two miles thick in winter. Sometimes, giant dust storms cover up to half the planet and dust devils and giant tornadoes have been spotted blowing across the surface. Curiosity has discovered phosphates in the martian soil. This suggest that crops could be grown in Martian greenhouses. So far, no evidence has been discovered that life ever existed on Mars, but we’re still searching. Loss of the Magnetic Core Mars is commonly known as the Red Planet. Recently, it was confirmed that liquid water still flows on the surface. It has two small moons, Phobos and Deimos. At one time, Mars had a spinning molten core that produced a magnetic field. Together with gravity, this field allowed an atmosphere and liquid water to form on its surface. But at some point, the magnetic field was lost. The loss of the magnetic field means Mars is subjected to solar radiation. Gradually, the atmosphere dissipated into space. Water also dissipated into space and some of it flowed under the surface of the planet and froze. 12 The Outer Planets Four gas giant planets make up the outer reaches of our solar system. Little was known of these worlds before the 1980s. J UPITER THE K ING OF THE P LANETS Moons: 67 moons. Major Moons: Europa, Callisto, Io and Ganymede (known as the Galilean moons because they were discovered by Galileo). Distance from Sun: 483,766,653 miles or 5.2 AU Diameter: 86,881 miles Temperature range: 234 below 0° F Duration of Orbit (Jovian year): 11.8 Earth years Duration of Rotation (Jovian day): 10 Earth Hours Significant spacecrafts: Magellan, Voyager I and II, Juno (will reach Jupiter in 2016) Also known as: Marduk (Babylonian), Jove (sometimes we call things belonging to Jupiter as Jovian), Wood Star (Chinese: ⽊木星) Jupiter 14 Jupiter's Great Red Spot Jupiter is a gas giant planet, composed mainly of hydrogen and a little helium. There is also the presence of water and ammonia ice. Jupiter may have a solid or liquid core. Great Red Spot The most prominent feature of a Jupiter is a giant storm that has been raging for hundreds of years, perhaps much longer, called the Great Red Spot. However, recently, the red spot has been shrinking significantly. At one time, it was about three times the size of Earth, and now is only about size of the Earth. At present, no one knows why the storm continued for so long or why it is shrinking. Smaller spots appear and disappear from time to time. Other Features Horizontal cloud bands rotate across the face of Jupiter and sometimes change color. There may be several layers of clouds under the top layer and lightning has been observed. Jupiter has partial, faint rings only visible from spacecraft. Shoemaker-Levy 9 Comet The Red Spot has been shrinking in recent years and may be finally ending. The white spot below the Red Spot is about the same size of the Earth. In 1993, Jupiter was struck by a comet known as S-L9, nicknamed the “String of Pearls.” The S-L9 impact was the first time a cometary impact was observed on a planet in the solar system. In 2009, a new comet impact site was observed. 15 Jupiter’s Moons as seen through a telescope Significant Moons Callisto, Ganymede and Europa are covered with ice. Ganymede is the largest moon in the solar system. Ganymede is now believed to have a huge underground ocean containing more water than all the oceans of the Earth. Europa may have water geysers and a patch of organic clay on its surface. Europa may also have an underground ocean which might contain life. Io is covered with active volcanos that continually recover the surface with yellow and red sulfur. Normally, it is easy to see 4 to 6 of Jupiter’s moons even in small telescopes. 16 S ATURN THE M AGNIFICENT Moons: 63 moons, including 8 shepherd moons. Major moons: Titan and Enceladus Distance from Sun: 890,703,868 miles or 9.6 AU Diameter: 74,898 miles Temperature range: 310 below 0° to 220° below F Duration of Orbit (Saturnian year): 29.4 Earth years Duration of Rotation (Saturnian day): 11 Earth Hours Significant spacecrafts: Pioneer 11, Voyager I and II, Cassini-Huygens. The Huygens probe landed on the surface of Titan. Also known as: Cronos (Greek), Earth Star (Chinese: ⼟土星), Zuhal (Turkey) S ECTION 2 Saturn 17 Saturn and its Rings Saturn is a gas giant planet, composed mainly of hydrogen and a little helium, methane, plus water and ammonia ice. Rings The most striking feature of Saturn is its magnificent ring structure. There are 7 main rings (each one of these is made up of several individual strands). These rings are lettered A (the innermost ring) through G (the outermost ring). A large, empty gap in the rings is known as the Cassini division. There are two other significant, but smaller gaps. The rings are mainly made up of ice and dust. They may have been created when two or more moons collided, or are just made up of material that was left over from the creation of Saturn. The rings structure is kept intact by the gravity of small moons within the rings, known as shepherd moons. The rings are about 33 feet thick on average. Storms Saturn has a large six-sided (hexagonal) cyclone rotating on its North Pole. The very regular geometric phenomenon holds its unusual shape year after year, much like Jupiter’s great red spot. It is not known when or how this storm began or why it has six sides. Significant Moons Small moons, called shepherd moons, orbit inside the rings. Their gravity holds the rings together, keeping the ring particles from drifting away into space. Enceladus has water geysers and may have an underground ocean - and possibly even contain life. The ice erupting from its surface replenishes the ice in Saturn’s central rings. Titan, Saturn’s largest moon, has several large lakes, consisting of liquid methane and ice. Titan also has a thick atmosphere made of methane. 18 U RANUS , FORMERLY KNOWN AS G EORGE Moons: 27 moons Important moons: Titania, Oberon, Ariel and Miranda. Distance from Sun: 1, 787,484,958 miles or 19.2 AU Diameter: 31,763 miles Temperature: 371° below 0 F, the coldest planet in the solar system Duration of Orbit (Uranian year): 84.3 Earth years Duration of Rotation (Uranian day): 17 Earth Hours Significant spacecraft: Voyager II Also known as: George’s Planet Uranus 19 Uranus Uranus is a gas giant planet, composed mainly of hydrogen and a little helium, methane, plus water and ammonia ice. Uranus is believed to have a rocky core surrounded by ice. Name Uranus is the only planet that uses a Greek, rather than a Roman, mythological name. It was not known in ancient times and was discovered after the invention of the telescope by William Herschel in 1781. Herschel originally named the planet after King George III of England, calling it George’s or the Georgian planet. The name was changed to Uranus, the name of Saturn’s father in Greek mythology. Uranus’ moons are named after characters in Shakespeare’s plays. Rings Uranus has a large ring structure made up of 13 rings. The rings were first photographed by the Voyager II satellite. The rings are mainly made up of ice and dust. They were probably created when two moons collided. These rings were not created at the same time as the planet. The rings are tilted and Uranus may have been struck by an Earth-sized object that knocked it on its side. A Hubble Space Telescope infrared image of Uranus and its rings. Uranus and Neptune belong to a group of planets known as Neptune Class planets. 20 N EPTUNE P LANET OF F IERCE W INDS Moons: 14 moons. Triton is the largest moon. Distance from Sun: 2, 798,309,291 miles or 30.1 AU Diameter: 30,775 miles Temperature: 218° below 0° F. Duration of Orbit (Neptunian year): 164.7 Earth years Rotation (Neptunian day): 16 Earth Hours Significant spacecraft: Voyager II. Neptune 21 Neptune’s Great Dark Spot Neptune is a gas giant planet, composed mainly of hydrogen and a little helium, methane, plus water and ammonia ice. Methane absorbs all colors except blue and gives both Uranus and Neptune their characteristic blue color. Neptune, like Uranus, is believed to have a rocky core surrounded by ice. It was not known in ancient times. Using mathematics, its position was predicted by both Urbain Le Verrier and John Couch Adams independently. It was finally observed in 1846 by Johannn Galle. Rings Neptune has a deteriorating ring structure. Some of the rings are not complete circles, but are made up of arcs – similar to Jupiter’s rings. The Great Dark Spot A large storm, known as the Great Dark Spot, raged on the surface of Neptune for about 20 years before blowing itself out. Winds blew at more than 1000 miles an hour, making it the fastest wind speed ever observed in the solar system. Moons The Dark Spot raged for twenty years with winds of 1000 miles per hour. The white areas are called scooters and are also storms. Triton is Neptune’s largest moon. Surface markings reveal that it once had geologically active geysers or volcanoes that erupted nitrogen. 22 Pluto and Beyond The frozen regions of the Kuiper Belt and the Oort Cloud populate the farthest regions of our solar systems. As the New Horizons spacecraft races through the Kuiper Belt, we will no doubt make new discoveries and uncover new mysteries. P LUTO E VERYONE ’ S FAVORITE Moons: 5 moons: Charon, Hydra, Nix, Styx, Kerberos Distance from Sun: 3, 649,825,210 miles or 43.1 AU Diameter: 1,433 miles (three-fourths the size of Earth’s moon) Temperature range : 400° below 0° F. Orbit (Plutonian year): 248 Earth years Rotation (Plutonian day): 6.3 Earth days (6 days, 8 hours) Significant spacecraft: New Horizons Pluto 24 Pluto’s atmosphere Pluto was not known in ancient times. It was discovered by Clyde Tombaugh in 1930. Tombaugh searched photographic images for two years to find the tiny world. Pluto is made up of rock and ice. Until New Horizons flew past Pluto in July 2015, very little was known of Pluto’s composition and features. Although instruments successfully captured scientific information during the Pluto flyby, data will continue to be transmitted about the flyby until October 2016 due to slow data transmission rates. Features Pluto has a copper red color and a large feature, resembling a heart. This region is made of methane ice, and has been named the Tombaugh Reggio, in honor of the discoverer of Pluto.. Pluto has flowing glaciers made of methane ice and a mountain range the size of the Rocky Mountains, made of water ice. Pluto has a thin atmosphere made up of nitrogen, methane, and carbon monoxide. Orbit It is sometimes closer to the Sun than Neptune, but is currently moving farther away again. New Horizons captured this image of Pluto, backlit by the Sun. The image reveals Pluto’s methane and carbon monoxide atmosphere. All the planets in the solar system follow a path call the ecliptic, the Earth’s orbital plane. However, Pluto is tilted to the ecliptic and moves above it and below it at an angle of about 17°. 25 Pluto and Charon Planet vs. Dwarf Planet Debate Pluto is no longer classified as a planet, but as a dwarf planet. When Pluto was discovered, no one knew exactly how big it was. If its true size had been known, it may never have been classified a planet to begin with. But as it was generally accepted as a planet, there was a huge public outcry when the IAU (International Astronomical Union) changed its classification to a dwarf planet. New Horizons has now accurately measured Pluto. and it is now known to be larger than Eris, confirming it is the largest dwarf planet. However, Pluto is smaller than our Moon. As New Horizons has revealed Pluto to be a complex world, the debate over its status has been re-ignited and a petition has been circulated to restore Pluto to full planet status again. Moons and a Double Planet System Nix is white with a red spot in its center. It is oval shaped and tumbles end over ends erratically. Kerberos is the only dark moon. It may have been formed outside of the Plutonian system and later captured by Pluto’s gravity. It may have even impacted with Pluto. Pluto and its largest moon, Charon, orbit each other. Nix (center right) is oval shaped and is white, with a red spot at its center. It tumbles erratically in its orbit. Pluto and Charon are tidally locked with each other – this means the same side of Pluto always faces the same side of Charon. However, Charon and Pluto orbit each other and are now considered to be a double (dwarf) planet or binary planetary system. 26 Kuiper Belt and Oort Cloud The Oort Cloud The Kuiper Belt Out past Neptune lies the icy region of space known as the Kuiper Belt. The Kuiper Belt is a lot like the asteroid belt, only 20 times wider and covering a region of 30 to 50 AUs beyond Neptune. Objects in the Belt are made up of ice and rock. The ice is made of water, methane and ammonia. Pluto is the first member of the Kuiper Belt, followed by the other dwarf planets Eris, Makemake and Haumea. Between 40 and 200 frozen worlds may inhabit the Belt. Not much is known about this distant regions of our solar system. As the New Horizon spacecraft travels deeper into the Kuiper Belt, we will no doubt make many unexpected discoveries. The Oort Cloud spherically surrounds the edges of the solar system with millions of ice particles. It is believed that this is where many comets come from. Halley’s comet and HaleBopp are the two most famous comets that originated in the Cloud. When large objects such as planets and stars pass nearby our solar system, their gravity bumps comets out of the region, sending them careening toward our Sun. We have not yet launched a spacecraft to the Oort Cloud. The Oort Cloud may begin an incredibly distant 2000 AUs from the Sun and may extend out to 100,000 AUs (this is half the distance to the nearest star, Proxima Centauri). 27 My Very Eager Mother At least that’s how the phrase used to read until Pluto was no longer considered a planet. So we have to come up with a new phrase. Here’s some other suggestions: My very eager mother just served us nachos. Or how about: There’s a simple phrase to help you remember the name and the order of the planets in our solar system: My very eager mother just served us noodles. Or perhaps: My very eager mother just served us nine pizzas. My very eager mother just served us nothing. My (Mercury) very (Venus) eager (Earth) mother (Mars) just (Jupiter) served (Saturn) us (Uranus) nine (Neptune) pizzas (Pluto). The position of each word is the order of the planets from the closest to the farthest from the Sun. We personally like nachos, but you can make up your own phrase, using all different words, if you’d like. Or you can keep the original phrase – a lot of folks still feel Pluto is important enough to be rub shoulders with the big guys! 28