Formation of a Solar System

Formation of Elements Originally, the universe only contain the element hydrogen. All of the other elements were forged in the cores of stars through a process called nuclear fusion. At the end of a stars life, the elements that were made in the core of a star are ejected into space. For stars life ours, only elements up to iron can be created, however when massive stars die they explode in a very violent eruption called a supernova (figure 1). Supernova explosions create so much energy elements larger than iron, like gold, silver, and uranium, are created. This “star dust” later clumps together into massive clouds of gas and dust called nebulas (figure 2). Figure 1. Picture taken from the Hubble telescope of a supernova event. Figure 2. Picture taken from the Hubble telescope of Pillars of Creation nebula.

Formation of the Sun Under the influence of gravity a nebula started to collapse on itself. While it was collapsing, it started to rotate. The rotation of the nebula caused the gas and dust particle to flatten into a disk. At the center, the tremendous pressure caused the temperature to rise. When the temperature at the center of the nebula reached about 15 million degrees Celsius, hydrogen atoms in the gas started to fuse to create helium atoms (nuclear fusion) and our Sun was created (figure 3). Figure 3. The diagram above shows the initial collapse of the nebula (a), the rotation causing a disk-shape to emerge (b), and finally the hydrogen gas to ignite creating the sun (c).

Formation of the Planets b While the Sun was forming, the dust grains that made up the nebula clumped together forming small rocks (figure 4). These rocks continued to grow in a process called accretion. Eventually through the same process the planets formed. In the inner part of the solar system four smaller rocky planets formed. Mercury, Venus, Earth, and Mars collectively known as the terrestrial (Earth-like) planets. The larger planets known as the gas giants or Jovian planets (Jupiter, Saturn, Uranus, and Neptune) formed in the outer solar system. All are believed to have rocky cores about the size of earth which are covered with thick atmospheres of liquid and gaseous hydrogen. Beyond the orbit of Neptune lies a massive belt of asteroids, comets, and dwarf-planets like Pluto known as the Kupier belt (figure 5) . You can think of it like the asteroid belt found between the orbits of Mars and Jupiter, however the Kupeir belt is many times more massive and is primarily composed of icy bodies of water, methane, and ammonia. Figure 4. The diagram above shows dust drains swirling around the early sun (a). Later, those dust grains grew to large rocks, which eventually led to the planets we have today. Figure 5. The diagram above shows the Kupier belt.

Formation of the Moon When the solar system was still very young, there is thought to have been many smaller planets. As you can see from figure 6, many of these smaller planets had orbits that passed the larger planets. About 50 million years after the formation of the earth, a Mars-sized planet collided with Earth, tearing off the part of Earth’s crust and upper mantle. The energy associated with this impact melted both earth and the smaller planet, but it also ejected rock into orbit around the earth. The debris from this collision would coalesce into the moon (figure 7). Figure 6. The diagram above shows how the early solar system had many smaller planets with overlapping orbits. Figure 7. The diagram above shows the formation of the moon.