Differentiation Between Terrestrial and Gas Giant Planets

The eventual type of planet that forms depends on its distance from the star and the materials available in that region of the disk. The disk can be divided into two key regions:

• Inner disk (closer to the star): In this region, temperatures are too high for volatile compounds like water and methane to condense into solids. As a result, rocky and metallic materials dominate, leading to the formation of terrestrial planets like Earth and Mars, which are made primarily of silicate rocks and metals.

• Outer disk (farther from the star): In the cooler regions of the disk, ices such as water, ammonia, and methane can solidify, providing more material for planetary growth. This allows for the formation of gas giants like Jupiter and Saturn, which have large rocky or icy cores surrounded by thick layers of gas (mostly hydrogen and helium).

5. Core Accretion of Gas Giants

In the outer regions of the protoplanetary disk, the cores of gas giants form in a similar way to terrestrial planets. However, once these cores grow large enough (around 10 Earth masses), they start to gravitationally attract and accrete gas from the surrounding disk at a rapid rate.

• This process forms the massive atmospheres of gas giants like Jupiter and Saturn.
• Ice giants such as Uranus and Neptune form similarly, but their cores don’t capture as much gas, leading to smaller atmospheres dominated by heavier elements like water, ammonia, and methane.

6. Clearing of the Protoplanetary Disk

As the protostar evolves into a main-sequence star, it emits intense radiation and stellar winds that gradually blow away the remaining gas and dust in the disk. This clears the protoplanetary disk of material, halting the growth of any planets still forming.

At this stage, most planets have reached their final size, and the debris that is left over can form other small objects like moons, asteroids, and comets.

7. Late-Stage Collisions and Planetary Migration

After the protoplanetary disk has been cleared, planetary formation is not entirely finished. Some protoplanets may still exist and can collide with each other, merging into larger planets. These late-stage collisions can drastically reshape a planet’s characteristics. For example:

• The Moon is believed to have formed as a result of a giant impact between a Mars-sized body and the early Earth.
• Mars-sized objects may also have collided with other protoplanets, altering their orbits and characteristics.

In addition, planets can undergo planetary migration, a process in which interactions with the gas disk or other planets cause planets to shift from their original orbits. This is especially true for gas giants, which are thought to have migrated inward after forming farther out from the star.

Conclusion

The formation of planets is a dynamic and multi-step process that starts with the creation of a protoplanetary disk around a young star and ends with the birth of fully-fledged planets. Through accretion, collision, and migration, planets are shaped into the diverse bodies we observe today. Understanding how planets form helps scientists not only explain the variety of planets in our own