Gas Giants Defined

When discussing giant planets, we typically focus on those within our Solar System, specifically Jupiter and Saturn, which classify as gas giants.

In contrast to terrestrial planets, gas giants exhibit considerably lower average densities. They are primarily made up of hydrogen and helium, yet their internal structures remain largely mysterious. Within Jupiter and Saturn, hydrogen and helium are subjected to extreme compression due to immense pressure, with theoretical estimates suggesting that core pressures may exceed 100 million bars.

Under such extreme conditions, materials that are familiar to us on Earth can undergo unusual transformations. As one descends thousands of kilometers beneath the visible cloud layers of Jupiter and Saturn, the pressure becomes so intense that hydrogen transitions from a gaseous state to a liquid form, creating an ocean of liquid hydrogen. This transition is relatively gradual. Further down, this liquid hydrogen becomes increasingly compressed, eventually transitioning into a solid or metallic state, thereby exhibiting characteristics similar to conventional metals. Because this transition is smooth, gas giants do not possess a definitive solid surface or a clear liquid boundary.

Each gas giant harbors a core made up of heavier elements. These cores, which are rocky and icy, formed prior to the planet’s accumulation of gas from the surrounding nebula. They are subject to pressures reaching tens of millions of bars and primarily consist of carbon, iron, nitrogen, silicon, and oxygen, combined with hydrogen. Notably, Jupiter is particularly fascinating, as it radiates more energy than it absorbs from the Sun. This excess heat is attributed to radioactive decay and the energy released by heavy elements settling towards the core.

The first video, "What if we were to remove the gas from gas giant planets?" explores the intriguing possibilities of what gas giants would look like without their gaseous envelopes.

Ice Giants: A Different Class

Another captivating category of giant planets is the ice giants, which include Uranus and Neptune. These planets differ markedly in both composition and internal structure from their gas giant counterparts.

Uranus and Neptune contain some hydrogen and helium, but also include heavier elements such as oxygen, carbon, nitrogen, and sulfur. The cores of these ice giants are significantly larger in proportion compared to those of gas giants and lack a substantial layer of metallic hydrogen, as illustrated below. This distinction is why they are referred to as ice giants, a term that emerged in the 1990s when researchers recognized their compositional differences from Jupiter and Saturn.

Unlike terrestrial planets, giant planets do not have solid surfaces. Their makeup predominantly consists of various gases in different states across multiple layers. At their core, amidst immense pressure, lies a mixture of rock and ice.

The second video, "Exploring Gas Giants," provides a detailed look at the characteristics and mysteries of gas giants within our solar system.