Why are the gas planets found further from the sun that the rocky ones?
The position of gas planets, such as Jupiter and Saturn, being further from the Sun compared to rocky planets like Earth is due to the process of planetary formation. To completely understand this, let's break it down into several steps:
1. Formation of the Solar System: The Solar System formed approximately 4.6 billion years ago from a gigantic, rotating disk of gas and dust known as the protoplanetary disk. This disk was primarily made up of hydrogen and helium, along with other heavier elements.
2. Differentiation: As the protoplanetary disk slowly contracted, it began to spin faster due to the conservation of angular momentum, causing it to flatten into a disc shape. In the central region of this disk, where it was hottest and denser, rocky materials (known as silicates) condensed and stuck together through a process called accretion, forming the inner rocky planets like Earth, Mercury, Venus, and Mars.
3. The Frost Line: However, farther from the Sun, beyond a particular distance known as the "frost line" or "snow line," the temperature dropped significantly. Beyond this point, volatile substances such as water, methane, ammonia, and other gases were able to condense and form solid ice grains, alongside rocky materials.
4. Gas Accretion: In the outer regions of the protoplanetary disk, where the temperature was low enough for gases to remain in a solid or liquid state, the increased density of these icy particles led to the formation of massive planetesimals. Over time, these planetesimals continued to grow through collisions and gravitational interactions, accumulating more and more gas. The gas giants, like Jupiter and Saturn, formed in these outer regions because of their ability to accumulate a significant amount of gas due to their massive gravitational attraction.
5. Migration of Gas Giants: It is believed that after their initial formation, gas giants underwent a process called "migration." Gravitational interactions with the remaining gas in the protoplanetary disk caused them to slowly move inward or outward, depending on numerous factors, including their masses and the distribution of gas in the disk. This migration process led to the gas giants' final positions, with them ending up further from the Sun than the rocky inner planets.
In summary, the rocky planets formed closer to the Sun where it was hotter, and silicate-based materials condensed in the protoplanetary disk. Beyond the frost line, where it was colder, volatile gases could condense and solidify, allowing for the formation of gas giants like Jupiter and Saturn.