Saturn, the solar system’s second-largest planet, does not possess a solid, accessible surface like Earth or Mars. As a gas giant, its composition changes dramatically with increasing depth, transitioning from a gaseous atmosphere to a deep, liquid interior. Understanding what Saturn is “made of” requires examining its structure in layers, from the visible clouds down to its dense, innermost region.
Defining the “Surface” of a Gas Giant
Since Saturn lacks traditional solid ground, scientists use a defined reference point to measure its size and atmospheric characteristics. This conceptual surface is set at the atmospheric level where the pressure equals 1 bar. This pressure is approximately the same as the atmospheric pressure found at sea level on Earth. This 1-bar level provides a consistent datum point, even though it is entirely within the planet’s gaseous atmosphere.
Below this designated surface, a spacecraft would encounter increasingly dense fluid instead of solid ground. The atmospheric pressure and temperature rise continuously as one descends deeper into Saturn’s interior. The planet transitions gradually from gas to liquid, lacking a sharp boundary separating the atmosphere from the ground. The extreme conditions deep inside the planet would eventually crush and vaporize any human-made probe.
Chemical Composition of the Upper Atmosphere
The visible part of Saturn, its atmosphere, is predominantly composed of molecular hydrogen (\(\text{H}_2\)), making up about 96.3 percent of the volume, and helium (He), which accounts for about 3.25 percent. While this is the primary composition, the colors and bands we observe are created by trace elements condensing into clouds. The outermost, most visible layer of clouds is made of frozen ammonia crystals.
Below the ammonia layer, increasing pressure and temperature cause other chemical compounds to condense. The next layer down is predicted to consist of ammonium hydrosulfide (\(\text{NH}_4\text{SH}\)) crystals. Deeper still, where temperatures approach the freezing point of water, scientists predict the existence of clouds composed of water ice. Trace amounts of methane, ethane, and phosphine are also present, contributing to the planet’s yellowish, hazy appearance.
The Transition to Liquid Metallic Hydrogen
Beneath the swirling gaseous atmosphere, immense pressure causes molecular hydrogen to undergo a profound physical change. As depth increases, the hydrogen compresses into a dense, non-ideal liquid state. Farther down, the pressure becomes so extreme that it strips the electrons from the hydrogen atoms’ nuclei, transforming it into a highly conductive fluid.
This exotic substance is known as liquid metallic hydrogen. It behaves like a metal because its electrons move freely, allowing it to conduct electricity. This vast layer constitutes the majority of Saturn’s volume. The movement of this electrically conductive fluid generates Saturn’s powerful planetary magnetic field, a process similar to the dynamo effect in Earth’s core.
The Dense Internal Core
Deep inside the liquid metallic hydrogen layer lies the planet’s innermost region, a dense core of heavier elements. Based on gravitational studies, this core is estimated to be composed of rock, primarily silicates, and various ices, such as water, methane, and ammonia. The mass of this central region is significant, possibly ranging from 9 to 22 times the mass of Earth.
This material is often described as a “slush ball” or a diffuse region, rather than a solid, sharply defined sphere, as it is likely mixed with hydrogen and helium at its outer edges. This core exists under incredible pressure and heat, reaching temperatures of approximately 11,700 °C. The planet’s composition is a continuous, layered structure, progressing from gas to liquid to a highly compressed, dense central mass.