The Formation of Our Solar System
The prevailing model for the formation of the solar system is the nebular hypothesis.
1.Collapse: About 4.6 billion years ago, a small part of a giant molecular cloud of gas and dust (a solar nebula) collapsed under its own gravity.
2.Spinning Disk: As the cloud collapsed, conservation of angular momentum caused it to spin faster and flatten into a rotating protoplanetary disk.
3.Protostar Formation: The vast majority of the mass collected at the center, forming the Sun (a protostar at first). The immense pressure and temperature at the center ignited nuclear fusion.
4.Planet Formation (Accretion): In the surrounding disk, dust grains began to clump together through electrostatic forces, forming larger bodies called planetesimals. These planetesimals collided and merged, gradually growing into planets through a process called accretion.
Two Types of Planets
The temperature gradient in the protoplanetary disk led to the formation of two distinct types of planets:
Frost Line: An imaginary line in the disk beyond which volatile compounds like water, ammonia, and methane could condense into solid ice grains.
1.Terrestrial Planets (Inner Solar System):
Mercury, Venus, Earth, Mars.
Formed inside the frost line, where it was too hot for ices to condense.
Composed mostly of rock and metal.
They are small, dense, and have solid surfaces.
2.Jovian Planets (Outer Solar System):
Jupiter, Saturn, Uranus, Neptune.
Formed outside the frost line, where ices were abundant.
This allowed their initial cores to grow much larger, giving them enough gravity to capture huge amounts of hydrogen and helium gas from the nebula.
They are enormous, low-density 'gas giants' with no solid surface.
Other Solar System Objects
Asteroid Belt: A region between the orbits of Mars and Jupiter containing millions of rocky asteroids. It is thought to be the remnants of a planet that failed to form due to Jupiter's immense gravity.
Kuiper Belt: A region beyond the orbit of Neptune containing many small, icy bodies, including dwarf planets like Pluto.
Oort Cloud: A theoretical, immense spherical cloud of icy bodies surrounding the entire solar system, believed to be the source of long-period comets.