SOLAR SYSTEM

The region of the universe where we live in, the Solar System, is but one of many clusters of stars and planets in space. Our Solar System lies in a specific region of the universe which we have named ‘Milky Way Galaxy’. It consists of the Sun with 8 planets orbiting around it and also other bodies like dwarf planets and asteroids.

The Solar System originated some 4.6 billion years ago through the accretion of gases and dust grains. Four groups of objects constitute the Solar System: the Sun, the terrestrial planets (including Earth’s moon), the Jovian planets and their satellites, and the small bodies (asteroids and comets). Recent discoveries prove that our Solar System is not alone. Astronomers have discovered planets orbiting several other stars.

All the planets move around the Sun along the same direction, and nearly in the same orbital plane, the ecliptic plane. The ecliptic plane is roughly in the equatorial plane of the Sun’s rotation. The planets’ axes of rotation are almost perpendicular to this plane, with the exceptions of Uranus and Pluto, which are tilted on their sides. Of the numerous objects that orbit the Sun, most of the mass is contained within eight relatively solitary planets. The four smaller inner planets consisting of Mercury, Venus, Earth and Mars, also called the terrestrial planets, are primarily composed of rock and metal. The four outer planets called the gas giants, are substantially more massive than the terrestrials. The two largest among them 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 formation of the solar system commenced with the collapse of a fragment of an interstellar molecular cloud to a protoplanetary disk (the solar nebula) and continued through a complex process of accretion, coagulation, agglomeration, melting, differentiation and solidification to build the planets. Contributing to this were the secondary influences of aqueous alteration and thermal metamorphism and the tertiary effects of bombardment, collision, break-up and re-formation. Since all traces and vestiges of the original materials that formed the Earth have been obliterated by bombardment and by geological processing, the rocks that are accessible for study at the Earth’s crust are not representative of material that aggregated from the solar nebula. Thus the chronology of events that took place during the early solar system can only be determined by the study of meteorites and lunar material brought back to Earth by the Apollo and Luna missions.

Our current understanding of the Solar System and its formation is still under speculation. Astronomers need much more time before they can confirm a theory which presents a convincing explanation of all details of the formation and the evolution of planetary systems in general and of our solar system in particular.

Questions to Ponder

• What is the size of the Solar System?
• Where is the supernova remnant that led to our solar system?