How old is the solar system?
The solar system is about 4.5 billion years old. | Back to Top | 5. How big is the solar system? There are no physical boundaries in space. The traditional view of the solar system is that it consists of eight planets orbiting around one star: the Sun. Neptune, the farthest planet from the Sun, orbits at approximately 30 astronomical units (AU) from the Sun. An astronomical unit is a unit of length used by astronomers. One astronomical unit equals the average distance from Earth to the Sun — about 93 million miles (150 million km). The solar system also includes the Kuiper Belt, a comet-rich area that begins near Neptune’s orbit and stretches far beyond it, to about 50 AU from the Sun. Part of Pluto’s elliptical orbit extends far into the Kuiper Belt. Beyond Pluto’s orbit is another region of icy objects in our solar system, called the Oort Cloud, which extends approximately 50,000 AU from the Sun. | Back to Top | 6. Are there differences among the planets in our solar system? Planets
Current estimates put the age of the solar system at 4.5 billion years. There have been several theories advanced, over time, as to the origin of the solar system. The most widely accepted theory today is called the “modified nebular hypothesis.” It claims that the solar system was formed from an immense cloud of gas and dust (a nebula). Gravity and rotational forces caused the cloud to flatten into a disc. Much of the cloud’s mass drifted into the center and became the sun. The left over parts of the cloud formed small bodies called planetesimals. These planetesimals collided with each other, gradually forming larger and larger bodies, some of which became the planets. This process is thought to have taken about 25 million years. Sources: Moore, Patrick. Atlas of the Solar System, pp. 10-11; Van Andel, Tjeerd H. New Views On an Old Planet, p. 28.
