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Our Solar System How our Solar System is Formed Many First Nations and Métis peoples of Saskatchewan understand that celestial bodies like the Sun, the stars, and the Moon owe their origin to the Great Spirit. Turtle Island The story of Turtle Island and the Sky World is an example of a creation story that explains the existence of Earth (Turtle Island) and the heavens (Sky World). Some Haudenosaunee of Ontario believe that the Great Spirit (Gehi Mnidoo) fashioned both the sky and Earth. In the story, a woman fell from the Sky World, a place that existed like a dome over Earth. The animals of Earth, its only inhabitants in that time, rushed to help her, but without any land to rest upon, she would perish. The animals tried to find land and all of them failed, except Toad who dove deep into the ocean and brought up dirt in his mouth. The animals spread the dirt over the great Turtle’s back and created North America. Sky Woman cast up a handful of dust from the land, making the stars. Sky Woman then made the Sun and the Moon The Solar System Scientists describe our solar system as the Sun and all the planets and other celestial objects, such as moons, comets, and asteroids, that are held by the Sun’s gravity and orbit around it. The Nebular Theory The most accepted scientific theory on how the solar system was formed is called the nebular theory. A nebula is a cloud of dust and gases in space, which scientists believe is an area of star formation. The nebular theory explains that, after the Sun formed, the solar wind blew against the nebula from which it formed. This pushed the gas and dust away from the Sun. The leftover dust, gases, and other debris in the nebula that remained continued to spin, creating a thin disk around the new star. From within this disk, small bodies began to form, growing into the planets, moons, asteroids, and comets that make up the solar system. This process, astronomers believe, is how other star-and-planet systems in the universe have formed as well. The Sun The Solar and Heliospheric Observatory (SOHO), a solar space telescope, has had a clear view of the Sun since 1995. Our Sun is of medium size by star standards and is composed mainly of hydrogen (73 %) and helium (25 %). The rest is made up of heavier elements including carbon, oxygen, and iron. It formed in the same way that all stars do, taking shape inside a nebula. The Sun is believed to have first begun shining, or radiating energy, about 5 billion years ago and is expected to continue shining for about 5 billion years more before it runs out of fuel. Measuring Distances in Space The distances in space are so vast that astronomers developed special units of measure. One unit used to measure distances in space is the astronomical unit. One astronomical unit (AU) equals the average distance between the Sun and Earth, or the Diameter of Earth’s orbit, 1.49 x1011 m about 150 million km. Mercury is 0.39 AU from the Sun. This value is less than 1 AU because Mercury is closer to the Sun than Earth is. Mars is farther from the Sun than Earth is. It is 1.52 AU from the Sun. Measuring Distances in Space Outside the solar system, the distance to other celestial objects again becomes so great that even the AU is too small to be a useful unit of measure. Instead, astronomers usually use a unit called the light-year. One light-year (ly) equals the distance that a beam of light travels through space in 1 year. It is equivalent to 63 000 AU or 9000 billion km. At the speed of light, you could travel around Earth seven times in 1 s. Another measurement is the Parsec which is the average distance to the edge of our galaxy = 3.26 Light Years. Planets After the Sun, the next largest astronomical bodies in the solar system are the planets. A planet is an astronomical body that orbits one or more stars and is capable of forming into a spherical shape under its own gravitational force, or gravity. A planet does not create nor radiate its own energy like a star does. It only reflects the light of the star or stars that it orbits. The Rocky Inner Planets As the spinning particles of dust and gas slammed into each other during the early stages of the solar system’s formation, some of the particles began sticking together. As these objects got bigger in mass, gravitational forces caused them to contract and bind together even more strongly. Objects orbiting too close to the Sun gradually fell into it, drawn by its gravitational force. However, four large objects lasted and eventually formed the four rocky planets of the inner solar system: Mercury, Venus, Earth, and Mars. The Four Gas Giants Astronomers believe that the four largest planets in the solar system may have grown as they did because ice acted as a kind of glue to cause gas and dust particles in the outer regions of the solar system to stick together. The result was the four outer planets: Jupiter, Saturn, Uranus, and Neptune. They are often referred to as the gas giants because their atmospheres are made mostly of hydrogen and helium and because they are much larger than the inner planets. All of the gas giants are orbited by numerous moons. Jupiter and Saturn each have more than 60 moons A Different Theory on Solar System Formation Alan Boss proposes another theory of solar system formation. He believes the nebular theory does not explain the formation of the planets Uranus and Neptune. Although these planets are considered gas giants, they both have large rock and ice cores with a thin gas layer. Boss’s theory states that the formation of the outer planets was affected by another young star nearby. According to Boss, this star was much larger than the Sun, extremely hot, and emitted extreme UV radiation. A Different Theory on Solar System Formation The Sun’s gravity created a protective zone. Jupiter became the largest planet because it was fully protected. Saturn is smaller because it is located between the two star zones and had some of the available material diverted by the competing stars away from Saturn’s formation. Neptune and Uranus were closer to the larger star and similarly had materials stripped away from their formation. What was left condensed to form those two planets. The other star died and the Sun, along with our forming solar system, was pushed out of the nebula and sent to a calmer part of the galaxy Other Objects in the Solar System Many smaller objects exist in the solar system besides the eight planets. These include moons, comets, dwarf planets such as Pluto, and tiny grains of dust and ice. The Asteroid Belt Between the inner rocky planets and the outer gas giants lies a huge band of billions of rocks, spread out in a vast ring circling the Sun at a distance of about 3 AU. The Asteroid Belt These rocks are asteroids—metallic, rocky bodies without atmospheres that orbit the Sun but are too small to be classified as planets. This ring of rocky debris is known as the asteroid belt. Asteroids can range in size from 1000 km in diameter to the size of pebbles. Most asteroids are less than a kilometre in diameter. Asteroids Astronomers study asteroids for a number of reasons. One of these reasons is that many celestial bodies have hit Earth and the Moon. It is widely believed that 65 million years ago, a comet or asteroid hit Earth at three impact sites. The impact and the effects of the impact are believed to have caused the mass extinction of the dinosaurs. Asteroids The analysis of asteroids has given us the estimated age of the solar system. This is why asteroids are often known as “fossils.” By the 1950s, scientists had found a way to determine the age of many asteroid specimens. The oldest ones were dated at 4.56 billion years old. Since Earth would have formed at the same time as the asteroids did, researchers have used this asteroid-dating technique to date Earth. As it took time for the asteroids to form, the Sun and solar system are currently estimated to be about 5 billion years old. Dwarf Planets Dwarf planets are similar to planets in that they orbit the Sun and have a roughly spherical shape, but unlike planets, they have an unusual orbit or orbit in a zone that contains many other objects. The Story of Pluto Pluto was discovered in 1930 and was known as the smallest planet in the solar system and the ninth planet from the sun. Pluto is a dwarf planet. In 2003, an astronomer saw a new object beyond Pluto and thought he had found a new planet. This caused other astronomers to talk about what makes a planet a "planet." There is a group of astronomers that names objects in space. This group decided that Pluto was not really a planet because of its size and location in space. So Pluto and objects like it are now called dwarf planets. Protoplanets Similar to asteroids, dwarf planets are believed to have been created when the solar system formed. Using improved technologies, astronomers are able to gather more data about the dwarf planets. It is believed that the dwarf planet HL Tau b will one day become an actual planet. Scientists refer to these dwarf planets that are still forming as protoplanets. It will take a lot of time for this to occur, but by recording data, the question of how planets actually form may be answered. Comets A comet is a celestial object made of ice and dust, often called a “dirty snowball,” which travels in an elliptical orbit around the Sun. When a comet nears the Sun, the Sun heats the comet, causing some of its ice particles to break away. Carried away from the Sun by the solar wind, these icy particles spread out into a tail millions of kilometres long and are lit up by reflecting the Sun’s light. Comets The brightness of a comet depends on two things: how close the comet is to the Sun, which controls the comet’s activity, and how close the comet is to Earth. Astronomers have been recording the appearance of comets since 2000 BCE. Scientists believe that comets were created from the same nebula that formed the planets. Comets Some believe that the ice that surrounds comets plays an important role in the creation of oceans and atmospheres. As a comet or asteroid comes close to Earth, there is the possibility that it will fall from orbit and collide with Earth. Astronomers have developed the Torino Scale to help communicate the possibility of such a collision. The scale ranges from 0 to 10, where 0 indicates little or no impact and 10 is a collision that would cause global climatic change. A Deathly Collision Evidence shows that a comet or asteroid hit Earth 65 million years ago in the Yucatán Peninsula, in Mexico. This impact caused global tidal waves, worldwide firestorms, dust storms, and massive earthquakes. Scientists believe that these events caused the extinction of the majority of species on Earth, which included the dinosaurs. Meteors and Meteorites Meteoroids are small pieces of rock or metal that travel throughout the solar system with no fixed path. They are thought to be similar in origin to asteroids and comets. A meteor is a meteoroid that, upon entering Earth’s atmosphere, collides with gas molecules and the surface material is vaporized. Most meteors are not much bigger than a grain of sand. If a meteor does not burn up completely and strikes Earth’s surface, it is called a meteorite. For the Blackfeet Nation of Montana, a meteor event was an omen. It meant that either a great sickness would affect the tribe that winter or that a great chief had passed away. A greater than usual number of meteors can be seen during celestial events known as meteor showers.