The Solar System
The Solar System
The formation of the Solar System is theorized in accordance to the nebular hypothesis. This theory states that the Solar System emerged due to the gravitational collapse of a massive molecular cloud some 4.6 billion years ago. Research done on ancient meteorites reveals the presence of elements, these are found at the core of massive exploding stars. This indicates that the shockwave from a supernova explosion might have triggered the birth of the Sun within a star cluster. As the nebula collapsed within itself, the need to conserve the angular momentum made it rotate faster. The pressure, gravity and magnetic field caused the nebula to flatten out into spinning discs, with a dense protostar at the center. Millions of years later, the density of hydrogen in the center reached sufficient levels to start thermonuclear fusion. When the point of hydrostatic equilibrium was achieved, the thermal energy started countering the collapse, and the Sun became a full fledged star. The remaining debris and cloud of gas clumped together to form various planets.
The Solar System is broadly classified into three classes: the planets, dwarf planets and other celestial bodies. An object qualifies to be referred to as a planet if it has enough mass to form itself into a spherical shape, orbits the sun in fixed orbits and has cleared its immediate surroundings of any smaller objects. There are eight planets which satisfy these criteria they are, Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Until 2006, Pluto was considered to be the ninth planet; however it lost the status when numerous objects similar to the planet were discovered in the outer expanse of the universe. Notable amongst them was Eris, which was larger than Pluto. The planet is mow classified as a dwarf planet along with Eris and Ceres. The distances between celestial bodies are measured in terms of Astronomical Units (AU). One AU is approximately taken as the distance between the Earth and the Sun (148,598,000 km). Light year is another commonly used unit to measure celestial distances, one light year is around 63,240 AU. The solar system is casually divided into the inner Solar System and outer Solar System. The inner one comprises of the four terrestrial planets and the asteroid belt. Everything beyond the asteroid belt is considered to be outer Solar System.
The principal entity in the Solar System is the Sun which is a main sequence G2 star. The Sun makes up for 99.86% of the Solar System�s total mass and casts a dominating gravitational pull on it. Jupiter and Saturn account for 90% of the remaining mass. Most of the larger entities which orbit around the Sun are near the vicinity of �the plane of Earth�s orbit� referred to as ecliptic. The planets lie close to the ecliptic plane while the comets and asteroid belt objects are far off. All the planets and most of the Kuiper belt objects rotate counter clockwise as viewed from the Sun�s north pole .there are exceptions to this statement, the notable being Halley�s Comet. Objects traverse around the Sun in adherence to Kepler�s laws of planetary motion. The orbit of each object is at an approximate ellipse with the Sun being at one focus. The closer an object is to the Sun, the faster will be its movement. The orbital pattern of most of the planets are almost circular, however certain comet, asteroids follow exceedingly elliptical orbits.