Geology (The Planet Earth-I) UNIT-1 The Planet Earth-I 1. ORIGIN OF THE SOLAR SYSTEM AND EARTH The Solar System The Solar System is made up of all the planets that orbit our Sun. In addition to planets, the Solar System also consists of moons, comets, asteroids, minor planets, and dust and gas. Everything in the Solar System orbits or revolves around the Sun. The Sun contains around 98% of all the material in the Solar System. The larger an object is, the more gravity it has. Because the Sun is so large, its powerful gravity attracts all the other objects in the Solar System towards it. At the same time, these objects, which are moving very rapidly, try to fly away from the Sun, outward into the emptiness of outer space. The result of the planets trying to fly away, at the same time that the Sun is trying to pull them inward is that they become trapped half-way in between. Balanced between flying towards the Sun, and escaping into space, they spend eternity orbiting around their parent star. Our solar system consists of an average star we call the Sun, the planets Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus, Neptune, and Pluto. It includes: the satellites of the planets; numerous comets, asteroids, and meteoroids; and the interplanetary medium. The Sun is the richest source of electromagnetic energy (mostly in the form of heat and light) in the solar system. The Sun's nearest known stellar neighbor is a red dwarf star called Proxima Centaury, at a distance of 4.3 light years away. The whole solar system, together with the local stars visible on a clear night, orbits the center of our home galaxy, a spiral disk of 200 billion stars we call the Milky Way. The Milky Way has two small galaxies orbiting it nearby, which are visible from the southern hemisphere. They are called the Large Magellanic Cloud and the Small Magellanic Cloud. The nearest large galaxy is the Andromeda Galaxy. It is a spiral galaxy like the Milky Way but is 4 times as massive and is 2 million light years away. Our galaxy, one of billions of galaxies known, is traveling through intergalactic space. The planets, most of the satellites of the planets and the asteroids revolve around the Sun in the same direction, in nearly circular orbits. When looking down from above the Sun's north pole, the planets orbit in a counter-clockwise direction. The planets orbit the Sun in or near the same plane, called the ecliptic. Pluto is a special case in that its orbit is the most highly inclined (18 degrees) and the most highly elliptical of all the planets. Because of this, for part of its orbit, Pluto is closer to the Sun than is Neptune. The axis of rotation for most of the planets is nearly perpendicular to the ecliptic. The exceptions are Uranus and Pluto, which are tipped on their sides. Composition Of The Solar System The Sun contains 99.85% of all the matter in the Solar System. The planets, which condensed out of the same disk of material that formed the Sun, contain only 0.135% of the mass of the solar system. Jupiter contains more than twice the matter of all the other planets combined. Satellites of the planets, comets, asteroids, meteoroids, and the interplanetary medium constitute the remaining 0.015%. The following table is a list of the mass distribution within our Solar System. Sun : 99.85% Planets : 0.135% Comets : 0.01% Satellites : 0.00005% Minor Planets : 0.0000002% Meteoroids : 0.0000001% Interplanetary Medium : 0.0000001% Contact Us : Website : www.eduncle.com | Email : [email protected] | Call Toll Free : 1800-120-1021 1 Geology (The Planet Earth-I) Interplanetary Space Nearly all the solar system by volume appears to be an empty void. Far from being nothingness, this vacuum of "space" comprises the interplanetary medium. It includes various forms of energy and at least two material components: interplanetary dust and interplanetary gas. Interplanetary dust consists of microscopic solid particles. Interplanetary gas is a tenuous flow of gas and charged particles, mostly protons and electrons -- plasma -- which stream from the Sun, called the solar wind. Fig. : Interplanetary Space The solar wind can be measured by spacecraft, and it has a large effect on comet tails. It also has a measurable effect on the motion of spacecraft. The speed of the solar wind is about 400 kilometers (250 miles) per second in the vicinity of Earth's orbit. The point at which the solar wind meets the interstellar medium, which is the "solar" wind from other stars, is called the heliopause. It is a boundary theorized to be roughly circular or teardrop-shaped, marking the edge of the Sun's influence perhaps 100 AU from the Sun. The space within the boundary of the heliopause, containing the Sun and solar system, is referred to as the heliosphere. The solar magnetic field extends outward into interplanetary space; it can be measured on Earth and by spacecraft. The solar magnetic field is the dominating magnetic field throughout the interplanetary regions of the solar system, except in the immediate environment of planets which have their own magnetic fields. The Terrestrial Planets The terrestrial planets are the four innermost planets in the solar system, Mercury, Venus, Earth and Mars. They are called terrestrial because they have a compact, rocky surface like the Earth's. The planets, Venus, Earth, and Mars have significant atmospheres while Mercury has almost none. The following diagram shows the approximate distance of the terrestrial planets to the Sun. Fig. : Mean Distances of terrestrial Planets from the Sun. Contact Us : Website : www.eduncle.com | Email : [email protected] | Call Toll Free : 1800-120-1021 2 Geology (The Planet Earth-I) The Jovian Planets Jupiter, Saturn, Uranus, and Neptune are known as the Jovian (Jupiter-like) planets, because they are all gigantic compared with Earth, and they have a gaseous nature like Jupiter's. The Jovian planets are also referred to as the gas giants, although some or all of them might have small solid cores. The following diagram shows the approximate distance of the Jovian planets to the Sun. Fig. : Mean distances of the Jovian Planets from the Sun. Origin of The Solar System Our solar system formed about 5 billion years ago, from an enormous cloud of dust and gas, a nebula. The Sun, like other stars, was formed in a nebula, an interstellar cloud of dust and gas (mostly hydrogen). These stellar nurseries are abundant in the arms of spiral galaxies (like our galaxy, the Milky Way). In the stellar nursery, dense parts of the clouds undergo gravitational collapse and compress to form a rotating gas globule. The globule is cooled by emitting radio waves and infrared radiation. It is compressed by gravitational forces and also by shock waves of pressure from supernova or the hot gas released from nearby bright stars. These forces cause the roughly-spherical globule to collapse and rotate. The process of collapse takes from between 10,000 to 1,000,000 years. The origin of the solar system has long been a fascinating subject posing difficult questions of deep significance. It takes one to the heart of the question of our origins, of how we came to be here and why our surroundings look the way they do. Unfortunately, we currently lack a self-consistent model for the origin of the solar system and other planetary systems. The early stages of planet formation are obscure, and we have only a modest understanding of how much the orbits of planets change during and after their formation. At present, we cannot say whether terrestrial planets similar to the Earth are commonplace or highly unusual. Nor do we know the source of the water that makes our planet habitable. In the face of such uncertainty, one might ask whether we will ever understand how planetary systems form. In fact, the last 10 years have seen rapid progress in almost every area of planetary science, and our understanding of the origin of the solar system and other planetary systems has improved greatly as a result. Planetary science today is as exciting as it has been at any time since the Apollo landings on the Moon, and the coming decade looks set to continue this trend. Contact Us : Website : www.eduncle.com | Email : [email protected] | Call Toll Free : 1800-120-1021 3 Geology (The Planet Earth-I) Some key recent developments follow : A decade ago, the first planet orbiting another Sunlike star was discovered. Since then, new planets have been found at an astounding rate, and roughly 200 objects are known today. Most of these planets appear to be gas giants similar to Jupiter and Saturn. Recently, several smaller planets have been found, and these may be akin to Uranus and Neptune, or possibly large analogs of terrestrial planets like Earth. In the last 10 years, there have been a number of highly successful space missions to other bodies in the solar system, including Mars, Saturn, Titan, and several asteroids and comets. Information and images returned from these missions have transformed our view of these objects and greatly enhanced our understanding of their origin and evolution. –presolar grains that The discovery that one can physically separate and analyze star dust —has can be extracted from meteorites and that formed in the envelopes of other stars meant that scientists can for the first time test decades of theory on how stars work. The parallel development of methods for extracting isotopic information at the submicron scale has opened up a new window to the information stored in such grains.