The French scientist who, in 1796, put forward a revised theory that the solar system formed from a slowly rotating, contracting cloud of hot gas was:

In 1796, the French mathematician and astronomer Pierre-Simon Laplace presented a revised version of the gaseous-cloud theory of the origin of the solar system in his book "Exposition du systeme du monde".

Laplace's hypothesis:

• The solar system began as a huge, hot, slowly rotating cloud of gas.
• As the cloud cooled, it contracted, and so it rotated faster.
• Because of the faster rotation, rings of material were thrown off from its outer edge.
• Each ring later condensed to form a planet, and the central part became the Sun.

Kant's earlier idea:

• In 1755, the German philosopher Immanuel Kant had proposed that the solar system formed from a slowly rotating cloud of gas and dust.
• Laplace developed the idea independently and gave it a more mathematical form.
• The combined idea is often called the Kant-Laplace hypothesis.

Criticism of the hypothesis:

• It could not explain why the Sun, which holds more than 99 percent of the mass of the solar system, rotates slowly and holds only a tiny fraction of its angular momentum.
• It could not clearly explain how separate rings would condense into planets.

Other theories of the origin of the solar system:

• Planetesimal hypothesis: Thomas Chamberlin and Forest Moulton (1904) suggested that a passing star pulled material from the Sun, which later formed small bodies called planetesimals.
• Tidal hypothesis: James Jeans and Harold Jeffreys (1917 to 1919) suggested that a passing star raised a cigar-shaped tidal filament from the Sun, which broke up into planets.

Modern view:

Today, scientists accept an updated version of the gaseous-cloud idea. The Sun and planets formed together from a rotating disc of gas and dust about 4.6 billion years ago.

Discs of this kind, called protoplanetary discs, have been observed around young stars.

Why not the other options?

• ✗Immanuel Kant proposed the original idea in 1755.
• ✗Johannes Kepler gave the laws of planetary motion.
• ✗Nicolaus Copernicus proposed the Sun-centred (heliocentric) model.