What Are Gas Giants?
Unlike the Solar System’s inner terrestrial planets, gas giants are large spheres of condensed gas, mostly hydrogen and helium. Like terrestrial planets, gas giants are rocky, formed from heavy elements left after the Sun’s formation. Gas giants emerged in the outer layers of the Solar System, where there were many lighter gaseous substances.
Two Groups of Gas Giants
There are four gas planets: Jupiter, Saturn, Uranus, and Neptune. While they are all similar, they can be divided into two groups. Jupiter and Saturn are substantially larger, and their chemical composition includes mostly hydrogen and helium. Uranus and Neptune are smaller and contain much more complex gases. The formation of Jupiter and Saturn, unlike Uranus and Neptune, made them much bigger.
The Process of Formation
According to the most confirmed hypothesis nowadays, in the beginning, they were similar to terrestrial planets: rocky and small spheres (Howell & Dobrijevic, 2022). As enormous amounts of hydrogen and helium gas were left after the Sun’s formation, these rocky cores started to grab gas around them. At first, it was like an atmosphere, but as gas condensed, it became a new planet’s surface, while the rocky core became extremely hot under its pressure.
Size and Composition Differences
In the case of Jupiter and Saturn, there was enough gas to let them grow bigger and contain mostly hydrogen and helium (Howell & Dobrijevic, 2022). Uranus and Neptune grabbed the gas remnants in the outer Solar System, becoming much smaller and collecting heavier and more complex compounds, including methane. Therefore, all four gas giants have similar formation mechanisms: they started as rocky planets, similar to inner terrestrial ones, but were covered with extreme amounts of gas left after the Sun was formed.
Similar Origins, Different Outcomes
However, they are different in their appearance and chemical composition due to the differences in their size and distance from the Sun. Crucial factors defined that Uranus and Neptune would be much smaller than Jupiter and Saturn, as they could not collect a similarly large amount of gas. Uranus and Neptune, unlike Jupiter and Saturn, are much smaller, and they contain much more complex gases, such as methane and ammonia. There is no principal difference in their formation mechanisms, but the outcomes are very different due to the different amounts of gas they can capture.
Reference
Howell, E., & Dobrijevic, D. (2022). Gas giants: Facts about the outer planets. Space. Web.