The Solar System refers to the area in space that is dominated by our own Sun. It is comprised of the Sun and its associated astronomical objects that are held in its gravitational orbit. The Solar System was formed as a result of the collapse of a giant molecular cloud approximately 4.6 billion years ago. The mass of this system is located almost entirely in the Sun. Apart from the Sun, a high percentage of the remainder of the system’s mass is located in the eight solitary planets that orbit the Sun. Their orbits are almost circular and lie within the nearly flat disc that is called the ecliptic plane. The eight planets have different and very distinct makeups. The smaller inner planets, Mercury, Venus, Earth and Mars, are known as the terrestrial planets, due to their primary composition of rock and metal. By contrast, the four outer plants, Jupiter, Saturn, Uranus and Neptune, known as the gas giants, have significantly more mass than the terrestrial planets. Jupiter and Saturn, the largest of the gas giants, are composed primarily of hydrogen and helium. The two planets on the outermost edges of the Solar System, Uranus and Neptune, are also known as ice giants as they are composed mainly of water, ammonia and methane ices. Pluto, until 2006, was believed to be the ninth planet in our Solar System. Astronomers in August of that year changed its designation to “dwarf planet”, as it is considerably smaller than its two ice planet neighbors. Pluto joined 44 other known dwarf planets that orbit our Sun.
Our system is located in an outer arm of the Milky Way galaxy. The Milky Way is known to contain some 200 billion stars. The outer spiral arm that contains our Sun is called the Orion-Cygnus Arm or Local Spur. Our system lies somewhere between 25,000 and 28,000 light years from the Galactic Center. The Sun, itself, travels approximately 721784.777 feet per second. Its revolution is known as the Solar System’s galactic year and is completed every 225-250 million years.
Dwarf planets are objects locked in orbit of the Sun that are large enough to have their shape rounded by their gravity. Other smaller objects also populate space. The asteroid belt, located between Mars and Jupiter, shares similarities with the terrestrial planets due to their shared composition of rock and metal. Two outer regions in our Solar System, the Kuiper belt and scattered disc, lie beyond Neptune and share traits with the ice giants. Cosmic entities such as comets, centaurs and interplanetary dust travel freely between all of the separate regions of our Solar System. Six of the planets and three of the dwarf planets have natural satellites. We often refer to them as moons due to their resemblance to our own moon. The four outer planets are each encircled by planetary rings of dust and other particles.
The existence of the Solar System has not always been evident. Prevailing wisdom of the day led most to believe the Earth was stationary in the Cosmos and all astronomical phenomena that occurred were in movement through our sky. In the early to mid-1500’s, Nicolaus Copernicus, a university-trained priest who was meant to focus on astronomy circulated his mathematically predictive heliocentric system. His findings gained popular acceptance in the 1600’s with the assistance of the fathers of the field of physics, Galileo Galilei, Isaac Newton and Johannes Kepler. They came to understand that not only does the Earth move around the Sun, but that all planets in the Solar System are governed by the same laws of physics that govern the Earth.
As discussed above, our Sun, a G-2 main-sequence star, is a massive and dominant entity. It holds 99.86 percent of the Solar System’s known mass. The four outer gas giants comprise 99 percent of the remaining .14 percent of the known mass in our system. The Sun, when viewed from above its north pole, rotates in a counter-clockwise fashion. Each of the eight planets, along with most other astronomical objects, orbit the Sun in the same counter-clockwise direction.
Johannes Kepler developed laws governing planetary motion. Kepler’s laws detail how each object travels along and ellipse with the Sun at one focus. They show how objects, such as Mercury and Venus, due to their relative proximity to the Sun, travel more quickly as a result of the Sun’s gravity on them. Though appearing almost circular, each planet travels in an elliptical orbit which brings about changes in the overall distance each planet has in relation to the Sun. When an object is closest to the Sun it experiences its perihelion. The opposite of this, the aphelion, occurs when an object is at its farthest approach to the Sun.
To date, no laws have been accepted by the scientific community regarding orbital spacing. On many graphic representations of our Solar System, the planets are often shown as having equidistant spacing of their orbits. In actuality, each planets orbit is, in relation to the preceding planet, quite a bit further away from the Sun. To understand this concept, Mercury, at is perihelion is approximately 28.5 million miles from the Sun. The next planet, Venus, at its closest point to Mercury, is 31 million miles away. The Earth is estimated to be 41 million miles from the orbit of Venus, at their closest proximity.
Solar winds, derived from a flow of plasma from the Sun, create what is known as the heliosphere. The heliosphere extends to the outer edge of the scattered disc. The energy from the Sun travels all the way to what is known as the heliopause. This is the region where pressure from solar wind becomes equal to the opposing pressure of interstellar wind. Solar wind played a fundamental role in ending the planetary formation process. Once the Sun, in its protostar phase, achieved a pressure and density of hydrogen to begin thermonuclear fusion, the temperature, reaction rate, pressure and density increased until a hydrostatic equilibrium was reached. This meant that both gravity and thermal pressure equaled one another. This let our Sun become a main-sequence star. Solar winds, in creating our heliosphere, were able to push out the remnant gas and dust from the protoplanetary disk into interstellar space.
The Solar System that we know and inhabit today is expected to remain in this form for approximately another 5.4 billion years. It is anticipated this will be the time in the Sun’s lifecycle when the hydrogen in its core will have been entirely converted to helium. With this occurrence, the Sun’s main-sequence life will come to an end. The core of the Sun will collapse producing a much greater energy output than at present. The outer layers of the Sun will expand to roughly 260 times its current diameter. This is the moment the Sun will have become a red giant. As its surface area experiences this drastic increase, the actual surface of the Sun will become considerably cooler than it is on the main sequence. The rapid expansion will vaporize Mercury and Venus as well as render the Earth uninhabitable. The habitable zone will have moved out to the orbit of Mars. The next expected process will begin when the core of the Sun becomes hot enough for helium fusion to begin. As the size of the Sun won’t allow it to sustain fusion of heavier elements, it will only burn helium for a small fraction of the time that it burned hydrogen. As nuclear reactions in the core happen with far less frequency, the Sun will begin to break apart, dispersing its outer layers into space. These ejected layers will form what is known as a planetary nebula. It will be the basic material that formed the Sun combined with heavier elements, like carbon. What will be left of the Sun, itself, is a white dwarf, an object that is remarkably dense. It will be comprised of approximately half the mass the Sun now currently possesses but packed into an Earth-sized object.
To read on individual components of our Solar System, we have provided the following links for you:
- The Asteroid Belt
- Trans-Neptunian region
- Kuiper Belt
- The Scattered Disc
- Oort Cloud
Image Caption: Planets and dwarf planets of the solar system. Credit: Farry/Wikipedia