Jovian planets, also known as gas giants, have thick atmospheres compared to terrestrial planets due to several factors:
Composition: Jovian planets consist mainly of hydrogen and helium, which are the most abundant elements in the universe. These elements make up the bulk of their atmospheres. Terrestrial planets, on the other hand, have a much smaller percentage of these light gases in their atmospheres and are composed mostly of heavier elements like oxygen, nitrogen, and carbon dioxide.
Gravitational pull: Jovian planets are much larger and more massive than terrestrial planets. Their stronger gravitational pull allows them to retain a greater amount of gas in their atmospheres. The higher escape velocities of Jovian planets prevent the gases from escaping into space, whereas terrestrial planets have lower escape velocities, leading to the loss of lighter gases over time.
Lack of solid surfaces: Jovian planets do not have a solid surface like terrestrial planets do. Instead, their atmospheres gradually transition into dense, liquid or metallic hydrogen layers. Without a solid surface, there is no clear boundary between the atmosphere and the planet itself. The lack of a solid surface allows the gases to mix and extend to great depths, contributing to the thickness of the atmosphere.
Energy input: Jovian planets receive a significant amount of energy from their host star. This energy, primarily in the form of sunlight, heats up the atmosphere and drives atmospheric processes such as convection and circulation. The energy input sustains the dynamic and turbulent nature of the atmosphere, leading to the maintenance of a thick and active gaseous envelope.
In contrast, terrestrial planets have thinner atmospheres because their lower masses and gravitational forces make it more challenging to retain lighter gases. Additionally, the solid surfaces of terrestrial planets limit the vertical extent of their atmospheres and provide a clear distinction between the planet's surface and its atmosphere.
It's important to note that our understanding of exoplanets is continually evolving, and there is still much to learn about the diversity of planetary atmospheres beyond our solar system.