The gas planets in our solar system are Jupiter, Saturn, Uranus, and Neptune. These four worlds are collectively called the “jovian planets” or “giant planets,” and they share a key trait: unlike rocky planets such as Earth and Mars, they have no solid surface you could stand on. Scientists further divide them into two subcategories. Jupiter and Saturn are “gas giants,” made mostly of hydrogen and helium. Uranus and Neptune are “ice giants,” with interiors dominated by heavier compounds like water, ammonia, and methane.
Gas Giants vs. Ice Giants
Jupiter and Saturn earn the label “gas giant” because hydrogen and helium make up the vast majority of their mass. Saturn’s atmospheric helium content is roughly similar to Jupiter’s, and both planets closely mirror the composition of the Sun itself. Think of them as stars that never gathered quite enough material to ignite nuclear fusion.
Uranus and Neptune are a different story. While they still have outer atmospheres of hydrogen and helium, about 98 percent of those lighter gases were lost during formation, leaving interiors rich in water, ammonia, and methane compressed under extreme pressure. That compositional difference is why astronomers classify them separately as ice giants, despite “ice” being a bit misleading. The compounds inside these planets exist as superheated, pressurized fluids rather than anything resembling the ice in your freezer.
How Big Are They?
Jupiter dwarfs everything else in the solar system. It is more than 1,300 times Earth’s volume and roughly 318 times Earth’s mass. Saturn is the second largest, famous for being less dense than water (in theory, it would float in an impossibly large bathtub). Uranus and Neptune are intermediate, much smaller than the gas giants but still about 4 times Earth’s diameter. All four are massive enough to hold large families of moons: Jupiter has 95 officially recognized moons, while Saturn holds the record at 274 confirmed moons after 128 new ones were verified in March 2025.
What’s Inside a Gas Giant?
Despite having no solid ground at the surface, these planets are not hollow balls of gas. Pressure increases dramatically toward the center, transforming their interiors into exotic states of matter. All four jovian planets share cores made of some combination of rock, metal, and hydrogen compounds. The real differences are in the layers above those cores.
On Jupiter and Saturn, the structure from the core outward goes: a core of rock and nickel-iron alloy, a layer of liquid metallic hydrogen, then liquid hydrogen, then gaseous hydrogen, and finally visible clouds at the top. Jupiter’s core temperature is estimated to exceed 20,000 degrees Celsius. The metallic hydrogen layer is especially important because hydrogen, squeezed under millions of times Earth’s atmospheric pressure, starts behaving like a liquid metal and conducts electricity.
Uranus and Neptune skip the metallic hydrogen layer almost entirely. Above their rocky cores sits a thick mantle of extremely hot fluid made of water, ammonia, and methane, topped by gaseous hydrogen and visible clouds. This simpler layering is another reason they get their own “ice giant” category.
Atmospheres and Storms
Each gas planet has a thick, turbulent atmosphere with dramatic weather. Jupiter’s Great Red Spot is perhaps the most famous storm in the solar system, a swirling anticyclone larger than Earth that has persisted for centuries. Saturn produces its own periodic megastorms, sometimes called Great White Spots, that can encircle the entire planet.
Neptune, despite being the farthest and coldest of the four, has the strongest winds in the solar system. At high altitudes, wind speeds exceed 1,100 miles per hour, which is 1.5 times the speed of sound. When Voyager 2 flew past Neptune in 1989, it photographed an Earth-sized storm called the Great Dark Spot, along with bright white clouds whipping around the atmosphere. Scientists later confirmed that these massive storms on Neptune are temporary, appearing and vanishing over years or decades.
Magnetic Fields
The metallic hydrogen inside Jupiter and Saturn does more than just sit there. It generates powerful magnetic fields through convection, much like molten iron generates Earth’s magnetic field. Jupiter’s magnetic field is about 20,000 times stronger than Earth’s, creating a magnetosphere so enormous that it begins deflecting the solar wind nearly 3 million kilometers out from the planet. Saturn’s magnetic field is proportionally weaker because its metallic hydrogen layer is smaller.
Uranus and Neptune lack metallic hydrogen in their interiors but still produce weak magnetic fields, likely generated by electrically conductive fluids deeper inside. Both planets have oddly tilted magnetic fields that don’t align well with their rotation axes, something scientists are still working to fully explain.
Rings Around Every One
Saturn’s rings are by far the most spectacular, visible even through a small backyard telescope. But all four giant planets have ring systems. Jupiter has faint, dusty rings discovered by the Voyager 1 spacecraft in 1979. Uranus has 10 narrow rings plus several fainter structures. The most prominent Uranian ring varies in width from 20 to 96 kilometers. Neptune has five named rings, all very faint and dusty, with one unusual feature: a set of bright arcs confined within a single 40-degree sector of its outermost ring.
How They Formed
The leading explanation for how gas giants came to exist is called the core accretion model. In the early solar system, small rocky and icy bodies called planetesimals clumped together through collisions and gravity. Once a core grew large enough, roughly 10 times Earth’s mass, its gravity became strong enough to capture enormous quantities of hydrogen and helium gas from the surrounding solar nebula. Jupiter and Saturn captured the most gas because they formed closer to the abundant material in the disk and grew their cores quickly. Uranus and Neptune, forming farther out where material was more spread out, built their cores more slowly and captured far less gas before the nebula dissipated. That timing difference is ultimately why we ended up with two gas giants and two ice giants rather than four of the same kind.