Saturn, the solar system’s sixth planet, is a gas giant instantly recognizable by its vast and complex ring system. It is the second-largest planet, a world of swirling hydrogen and helium. Earth, in contrast, is a small, dense, rocky terrestrial planet where liquid water and a temperate climate support life. Comparing these two worlds illuminates the immense diversity within our solar system, highlighting differences in composition, size, and environment.
Physical Scale and Structure
Saturn’s mean radius is roughly 9.1 times that of Earth, meaning its volume is so immense that over 760 Earths could fit inside the gas giant. Despite this enormous size, Saturn is only about 95 times more massive than Earth, a detail explained by its composition.
Saturn’s average density is extraordinarily low, sitting at less than that of water, a unique characteristic among all planets in the solar system. Earth possesses a high average density due to its interior structure of a solid iron core surrounded by a rocky mantle and crust. The gravitational pull at Saturn’s cloud tops is only slightly greater than Earth’s, approximately 1.065 times Earth’s gravity, because its massive size spreads that force over a much larger radius.
Atmospheric Environment and Composition
Earth’s atmosphere is primarily a mix of nitrogen (about 78%) and oxygen (about 21%), which sustains complex biological processes. Saturn’s outer atmosphere, however, is overwhelmingly composed of molecular hydrogen (about 96%) and helium, with trace amounts of methane and ammonia.
Descending into Saturn’s atmosphere reveals no solid surface; the gaseous layers become progressively denser and hotter due to immense pressure. This pressure eventually forces the hydrogen into a liquid metallic state deep within the planet, surrounding a presumed dense, rocky core. Earth’s surface pressure (one bar) is reached only in the uppermost regions of Saturn’s atmosphere, where temperatures average a frigid -139 degrees Celsius.
Saturn generates a significant amount of its own heat, radiating more energy than it absorbs from the distant Sun, suggesting an internal heat source from gravitational compression. Earth’s climate, conversely, is driven almost entirely by incoming solar radiation. The weather on Saturn is characterized by extreme wind speeds, reaching up to 1,800 kilometers per hour, far surpassing any wind speeds recorded on Earth.
Orbit and Time Scales
Earth orbits the Sun at a distance of one Astronomical Unit (AU), completing a full revolution in 365.25 days. Saturn orbits at an average distance of about 9.5 AU, roughly 1.4 billion kilometers from the Sun.
Saturn’s orbital period is exceptionally long, taking approximately 29.5 Earth years to complete a single circuit around the Sun. Despite its immense size, Saturn rotates surprisingly fast, completing a “day” in a mere 10 hours and 33 minutes, depending on the measured latitude. This rapid rotation causes Saturn to noticeably flatten at the poles and bulge at its equator.
Planetary Systems: Rings and Moons
Earth has only one large moon, which orbits a world with no ring system. Saturn is orbited by hundreds of moonlets and has at least 146 confirmed natural satellites, the most of any planet in the solar system.
The iconic rings are a complex structure composed almost entirely of billions of particles of water ice and some rocky debris, ranging in size from microscopic dust to house-sized chunks. The main ring system extends from approximately 7,000 kilometers to 80,000 kilometers above Saturn’s equator but is incredibly thin, measuring only about 10 meters thick in most places.
Saturn’s largest moon, Titan, is a unique satellite, even bigger than the planet Mercury. Titan is the only moon in the solar system to possess a substantial atmosphere, featuring a nitrogen-rich composition and surface lakes of liquid hydrocarbons.