Page 53 - Curriculum Visions Dynamic Book

information, we are still only scratching the surface.
We can begin to find out about how the Solar System formed by analyzing the materials that reach the Earth from space in the form
of meteorites.
The amount of this material that gets to Earth is surprisingly
large. Every day 400 tonnes of dust are added to the mass of the Earth by debris from asteroids and comets. You can start to see a way in which planets could grow when you consider the billions of years of Earth history. In the past, when there was much more material in space, the rate of growth would have been much faster.
Models of the origin of the Solar System
The first description of how the Solar System works was made possible using the laws of motion set out by Sir Isaac Newton in 1687. They explained how gravity affected bodies as well as why planets should orbit the Sun. Gravity is the force that draws space debris together and creates not just rocky planets like the Earth but gaseous planets and even the Sun.
A scientifically reasoned explanation of the origin of the Solar System was first suggested by Immanuel Kant in 1755. He believed that the Solar System started as a cloud of dust, and that gravity then made the dust particles move. As they did so, they collided and formed larger and larger bodies. Those that grew faster developed stronger gravity and began to attract more and more dust, thus growing faster still.
Pierre-Simon Laplace suggested that the planets were made from a gigantic star, or nebula, with an atmosphere (called the corona) stretching to the edges of the Solar System. He thought that the
star had cooled through time and so shrunk. The shrinking would have made it spin faster (as ice-skaters do when they spin and pull in their arms). That would tend to throw some material away from the star; but at the same time, most of it would be pulled inward by gravity. The result of these conflicting forces would be the creation of a disk of material. The planets would have formed in this disk.
This model explained why the Sun and the planets all move in more or less the same plane and in the same direction.
By the early 20th century Chrowder Chamberlin, Forest Ray Moulton, Sir James Jeans, and Sir Harold Jeffreys all decided independently that the planets were formed by the collision
corona (pl. coronae)
The gases surrounding a star such as the Sun. In the case of the Sun and certain other stars these gases are extremely hot.
gravity The force of attraction between bodies.
kuiper belt A belt of planetesimals (small rocky bodies, one kilometer to hundreds of kilometres across) much closer to the Sun than the Oort cloud.
laws of motion Formulated by Sir Isaac Newton, they describe the forces that act on a moving object.
meteorite A meteor that reaches the Earth’s surface.
nebula (pl. nebulae) Clouds of gas and dust that exist in the space between stars.
oort cloud A region on the edge of the Solar System that consists of planetesimals and comets that did not get caught up in planet making.
probe An unmanned spacecraft designed to explore our Solar System and beyond.
For explanations of
how galaxies and the universe may have formed see Volume 1: How the universe works.
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