March 19, 2019 Our Solar System By Sutirtha Datta Physical Geography 0 Comments Contents Sun Structure of the Sun SunspotsSolar Flares Solar Wind Difference between Terrestrial & Jovian planets Planets of our Solar SystemMercury Venus Mars Jupiter Saturn UranusNeptune Dwarf PlanetsAsteroid BeltKuiper BeltOort CloudMeteoritesComets Solar system originted from a nebula which started collapsing and core formation about 5 to 5.6 billion years ago. All planets were formed about 4.6 billion years ago. Our solar system consists of the sun (the star), 8 planets, many moons, millions of smaller bodies like asteroids and comets and huge quantity of dust-grains and gases. Out of the eight planets, mercury, venus, earth and mars are called as the inner planets as they lie between the sun and the belt of asteroids . They are also called Terrestrial, meaning earth-like as they are made up of rock and metals. They have relatively high densities. Other four planets are called the outer planets and also called Jovian or Gas Giant planets. Jovian means Jupiter-like. NASA’s Voyager-1 and Voyager-2 only two spacecrafts so far to leave our solar system. Sun Sun is a G2 star and revolves around the galactic core. It completes one revolution in 230 million years which is known as 1 Cosmic Year. It comprises about 99.86% of the mass of our Solar System. Sun is composed primarily of the chemical elements hydrogen and helium. Hydrogen converted into helium and energy has been produced by nuclear fusion. Sunlight at the top of Earth’s atmosphere is composed 50% infrared light 40% visible light 10% ultraviolet light Apparent rotational period of the Sun at its equator is about 28 days Average luminance of the Sun is about 1.88 Giga candela /m2, but as viewed through Earth’s atmosphere, this is lowered to about 1.44 Gcd/m2. Structure of the Sun Core Innermost 20-25% of the Sun’s radius, where temperature and pressure are sufficient for nuclear fusion Hydrogen fuses into helium. The fusion process releases energy Radiative Zone Between about 20-25% of the radius, and 70% of the radius, there is a radiative zone Tachocline the boundary region between the radiative and convective zones. Convective Zone Between about 70% of the Sun’s radius and a point close to the visible surface. Photosphere the deepest part of the Sun which we can directly observe with visible light. Photosphere has a temperature of around 6000°C Sunspots appears in photosphere Atmosphere A gaseous ‘halo’ surrounding the Sun, comprising Chromosphere – Plages occurs here, it is rosy red color, apparent during eclipses Solar transition region Corona – Outermost part of sun, Solar Flares occurs here Heliosphere – is the bubble-like region of space dominated by the Sun, which extends far beyond the orbit of Pluto. Sunspots Sunspots are darker, cooler regions on the bright, hot photosphere. Whilst the photosphere has a temperature of around 6000°C, sunspots are between 3000°C and 4000°C. They move across the surface of the Sun. Sunspots number varies according to the 11-year solar cycle. Galileo studied sunspots in 1610. Solar Flares Those are sudden variations in the brightness of a surface region of the Sun. Magnetic energy builds up in the solar atmosphere, above active regions Solar flares also pose a radiation hazard to astronauts in the International Space Station. Solar Wind Solar wind is a stream of energized, charged particles, primarily electrons and protons. It flows outward from the Sun, through the solar system. Speed of solar winds as high as 900 km/s and at a temperature of 1 million 0C. It is made of plasma. Solar winds affect the magnetic field of the Earth. Difference between Terrestrial & Jovian planets The terrestrial planets were formed in the close vicinity of the parent star where it was too warm for gases to condense to solid particles. Jovian planets were formed at quite a distant location. The solar wind was most intense nearer the sun; so, it blew off lots of gas and dust from the terrestrial planets. The solar winds were not all that intense to cause similar removal of gases from the Jovian planets. The terrestrial planets are smaller and their lower gravity could not hold the escaping gases Planets of our Solar System Mercury Mercury is the closest planet to the Sun. It is also the smallest planet in our Solar System. Mercury is made mainly of iron. After Earth it is the second most dense planet in our Solar System. It has no moon of its own. Big differences in day-time ( 427 °C) and night-time ( -173 °C) temperatures Orbital period of Mercury is 88 days. Venus Venus is the 2nd planet from the Sun. Orbital period of Venus is 224.7 days. It has the longest rotation period 243 days Venus rotates in the opposite direction to most other planets. The Sun would rise in the west and set in the east. It does not have any natural satellites Venus is the 2nd–brightest natural object in the night sky after the Moon. It has the densest atmosphere of the four terrestrial planets, consisting of more than 96% CO2. Venus is the hottest planet in our Solar System, with a mean surface temperature of 462 °C. It was the 1st planet to have its motions plotted across the sky as early as the 2nd millennium BC. Venus is the closest planet to Earth. It is similar to Earth in size and mass, and is often described as Earth’s “sister” or “twin” Venus was the first planet visited by a spacecraft (Mariner 2 in 1962, by NASA). Mangalyaan Mars Mars is the 4th from Sun and the 2nd smallest planet. Olympus Mons is the largest volcano, the tallest planetary mountain with height of 25km. Mars has two moons, Phobos and Deimos, may be captured asteroids. Mars trojans are a group of objects that share the orbit of the planet Mars around the Sun It having about 15% of Earth’s volume and 11% of Earth’s mass, resulting in about 38% of Earth’s surface gravity. Mars lost its magnetosphere 4 billion years ago. Atmosphere of Mars consists of about 96% CO2. Mars has polar ice caps. Mariner 9 was 1st successfully mission, 1971, landed a spacecraft on Mars. Mangalyaan, is a space probe orbiting Mars, was launched on 5 November 2013 by ISRO Jupiter Jupiter is the 5th from Sun the largest planet. Its volume is that of about 1,321 Earths. Jupiter and Saturn are gas giants; the other two giant planets, Uranus and Neptune, are ice giants. It has 79 known moons. Jupiter’s four largest moons Io, Europa, Ganymede and Callisto. Those were first observed by Galileo Galilei in 1610 using telescope. Io is the most volcanically active body in our solar system. Ganymede is the largest moon in the solar system. Jupiter has the same ingredients as a star, but it did not grow massive enough to ignite. It is composed of hydrogen and helium. Jupiter still radiates more heat than it receives from the Sun. It has the largest planetary atmosphere in our Solar System, spanning over 5,000 km in altitude. Jupiter has the shortest day in our solar system, only about 10 hours. It makes a complete orbit around the Sun in about 12 Earth years. Its magnetic field is 16 to 54 times as powerful as that of the Earth, causes some of the solar system’s most spectacular aurorae at the planet’s poles. 1st spacecraft to visit Jupiter was Pioneer-10 in 1973. Cassini Mission Saturn Saturn is the 6th fromthe Sun and 2nd largest planet. It has rings, that was first observed in 1610 by the astronomer Galileo Galilei Saturn is made mostly of hydrogen and helium. One day on Saturn takes only 10.7 hours. Saturn makes a complete orbit around the Sun in about 29.4 Earth years. Its axis is tilted by 26.73 degrees. It is the only planet in our solar system whose average density is less than water. Saturn’s rings are thought to be pieces of comets, asteroids or shattered moons that broke up before they reached the planet It has 82 moons, in which 53 moons are confirmed and named. Largest moon of Saturn is Titan. Pioneer 11 launched in 1973 was the 1st mission to Saturn by NASA. Cassini mission, was the most important launched in 2004 by NASA. Uranus Uranus is the 7th from Sun and 3rd largest. It is very cold and windy planet The ice giant is surrounded by 13 faint rings and 27 small moons as it rotates at a nearly 90-degree angle from the plane of its orbit. This unique tilt makes Uranus appear to spin on its side, orbiting the Sun like a rolling ball. Uranus is the first planet found with the aid of a telescope. It was discovered in 1781 by astronomer William Herschel. Uranus is 4 times wider than Earth. One day on Uranus takes about 17 hours. It makes a complete orbit around the Sun in 84 Earth years It is the only planet equator is nearly at a right angle to its orbit, with a tilt of 97.77 degrees Uranus also rotate in opposite direction like Venus, from east to west It has 27 known moons, being named for characters from the works of William Shakespeare and Alexander Pope Uranus has two sets of rings. Neptune Neptune is the 8th and most distant planet in our solar system. It is 30 astronomical units away from the Sun Neptune is the only planet in our solar system not visible to the naked eye Johann Galle discovered the planet in 1846. It is about four times wider than Earth One day on Neptune takes about 16 hours It makes a complete orbit around the Sun in 165 Earth years Of the giant planets, Neptune is the densest Its atmosphere is made up mostly of hydrogen and helium with just a little bit of methane Neptune is a vivid, brighter blue colored planet. It has 13 known moons, largest is Triton. Dwarf Planets It is a planetary-mass object that is neither a true planet nor a natural satellite That is, it is in direct orbit of a star, and is massive enough for its gravity to compress it into a hydrostatically equilibriums shape. The term dwarf planet was adopted in 2006. As of July 2008 the International Astronomical Union (IAU) recognizes five dwarf planets Ceres – 1801 Pluto – 1930 Haumea – 2004 Makemake – 2005 Eris – 2005 Asteroid Belt Asteroid Belt is a circumstellar disc in the Solar System. It is located between Mars and Jupiter. Asteroid Belt is occupied by numerous irregularly shaped bodies called asteroids or minor planets. Four largest asteroids Ceres Vesta Pallas Hygiea Ceres, the asteroid belt’s only dwarf plane. Kuiper Belt Kuiper Belt Objects (KBOs) first time came to light in 1992. It is approximately 50 AU from the Sun. Kuiper Belt is 20 times as wide and 20 to 200 times as massive then asteroid belt. It is the home to 3 recognized dwarf planets Pluto Haumea Makemake Oort Cloud Oort Cloud is believed to be a thick bubble of icy debris that surrounds our solar system It exists between 5,000 and 100,000 astronomical units from sun. Oort Cloud is too far to be seen with current telescopes, so it hasn’t been directly seen or discovered Scientists’ best guess about where long-period comets come from this region. Meteorites Little chunks of rock and debris in space are called meteoroids. Meteorite size can about be 1 to 5 meter. They become meteors or shooting stars, when they fall through a planet’s atmosphere. It leaves a bright trail as they are heated to incandescence by the friction of the atmosphere. Several times a year, Earth passes through a trail of debris creating meteor showers. Any of these debris that survive the journey and hit the ground are called meteorites. Comets Comets are icy small Solar System body. When passing close to the Sun, warms and begins to release gases, a process called outgassing. This produces a visible atmosphere or coma, and sometimes also a tail. Coma may be up to 15 times the Earth’s diameter, while the tail may stretch one astronomical unit. Comets usually have highly eccentric elliptical orbits. They have a wide range of orbital periods, ranging from several years to several millions of years. Short-period comets originate in the Kuiper belt. Long-period comets are thought to originate in the Oort cloud.