SOLAR SYSTEM

SOLAR SYSTEM

The Solar System consists of the Sun and the astronomical objects bound to it by gravity, all of which formed from the collapse of a giant molecular cloud approximately 4.6 billion years ago. Of the many objects that orbit the Sun, most of the mass is contained within eight relatively solitary planets whose orbits are almost circular and lie within a nearly flat disc called the ecliptic plane.

The earlier ninth planet Pluto was ripped off the planet status (by some sort of disciplinary action?) for being too small and for not following a unique path free from obstructions or for swaying into other planets’ orbits !

The four smaller inner planets, Mercury, Venus, Earth and Mars, also called the terrestrial planets, are primarily composed of rock and metal. One of the biggest stars, Antares is 700 times wider that the Sun, so that Mercury, Venus, Earth, and Mars would be orbiting deep inside it, if it was the sun!

The four outer planets, the gas giants, are substantially more massive than the terrestrials. The two largest, Jupiter and Saturn, are composed mainly of hydrogen and helium. The two outermost planets, Uranus and Neptune, are composed largely of ices, such as water, ammonia and methane, and are often referred to separately as ice giants.

The Solar System is also home to two regions populated by smaller objects. The asteroid belt, which lies between Mars and Jupiter, occupied by numerous irregularly shaped bodies called asteroids or minor planets, is similar to the terrestrial planets as it is composed mainly of rock and metal.

Beyond Neptune's orbit lie trans-Neptunian objects composed mostly of ices such as water, ammonia and methane. Within these two regions, five individual spherical objects, Ceres, Pluto, Haumea, Makemake and Eris, are recognized to be large enough to have been rounded by their own gravity, and are thus termed dwarf planets. In addition to thousands of small bodies in those two regions, various other small body populations, such as comets, centaurs and interplanetary dust, freely travel between regions.

Six of the planets and three of the dwarf planets are orbited by natural satellites usually termed "moons" after Earth's Moon. Each of the outer planets is encircled by planetary rings of dust and gas.

The Oort cloud is a hypothesized spherical cloud of comets which may lie roughly 50,000 AU, or nearly a light-year, from the Sun. This places the cloud at nearly a quarter of the distance to Proxima Centauri, the nearest star to the Sun. The Kuiper belt and scattered disc, the other two reservoirs of Trans-Neptunian objects, are less than one thousandth the Oort cloud's distance. The outer extent of the Oort cloud defines the gravitational boundary of our Solar System.

The Oort cloud is thought to comprise two separate regions: a spherical outer Oort cloud and a disc-shaped inner Oort cloud, or Hills cloud. Objects in the Oort cloud are largely composed of ices, such as water, ammonia, and methane.

Although no confirmed direct observations of the Oort cloud have been made, astronomers believe that it is the source of all long-period and Halley-type comets entering the inner Solar System and many of the Centaurs and Jupiter-family comets as well. The outer Oort cloud is only loosely bound to the Solar System, and thus is easily affected by the gravitational pull both of passing stars and of the Milky Way Galaxy itself. These forces occasionally dislodge comets from their orbits within the cloud and send them towards the inner Solar System. Based on their orbits, most of the short-period comets may come from the scattered disc, but some may still have originated from the Oort cloud.

The scattered disc is a distant region of the Solar System that is sparsely populated by icy minor planets, a subset of the broader family of Trans-Neptunian objects. While the nearest distance to the Sun approached by scattered objects is about 35 AU, their orbits can extend well beyond 100 AU. This makes scattered objects "among the most distant and cold objects in the Solar System".

Because of its unstable nature, astronomers now consider the scattered disc to be the place of origin for most periodic comets observed in the Solar System, with the centaurs, a population of icy bodies between Jupiter and Neptune, being the intermediate stage in an object's migration from the disc to the inner Solar System. Eventually, perturbations from the giant planets send such objects towards the Sun, transforming them into periodic comets. Many Oort cloud objects are also believed to have originated in the scattered disc.

The Kuiper belt (rhyming with "viper") is a region of the Solar System beyond the planets extending from the orbit of Neptune (at 30 AU) to approximately 55 AU from the Sun. It is similar to the asteroid belt, although it is far larger; 20 times as wide and 20 to 200 times as massive. Like the asteroid belt, it consists mainly of small bodies, or remnants from the Solar System's formation. While the asteroid belt is composed primarily of rock and metal, the Kuiper objects are composed largely of frozen volatiles (termed "ices"), such as methane, ammonia and water.

The Kuiper belt was initially believed to be the main repository for periodic comets, those with orbits lasting less than 200 years. However, studies since the mid-1990s have shown that the Kuiper belt is dynamically stable, and that comets' true place of origin is the farther scattered disc,

Pluto is the largest known member of the Kuiper belt. Originally considered a planet, Pluto's position as part of the Kuiper belt has caused it to be reclassified as a "dwarf planet

The Kuiper belt should not be confused with the hypothesized Oort cloud, which is a thousand times more distant. The objects within the Kuiper belt, together with the members of the scattered disc and any potential Hills cloud or Oort cloud objects, are collectively referred to as trans-Neptunian objects.

SOME INTERESTING COMPARISONS!

No.	Description	Figure
	Sun (Diameter)	109 times diameter of Earth
	Sun (Volume)	1.3 Million Earths
	Sun (Mass)	2 x 10^30 Kg.
	Sun (Weight)	332,950 times earth
	Earth (Mass)	6 x 10^24 Kg.
	Moon (mass)	7.35 x 10^22 Kg.
	Earth (Volume)	50 Moons
	Earth (Weight)	81 times moon
	Earth (Velocity)	107,300 km/hour or about 30 KM per Second !
	Jupiter	11 times diameter of earth.