The gas giants

This is our solar system. Close to the Sun, there are four rocky planets, one of them the Earth. And here, in the outer part of the solar system, there are four planets that are much larger than the rocky ones — Jupiter, Saturn, Uranus, and Neptune. These four planets are often described as gas giants. Each gas giant has a metallic, rocky, or ice core.

The core is surrounded by a very thick layer of light elements such as hydrogen and helium. There is no clear boundary between the planet and its gaseous atmosphere. All four planets have numerous moons, some of which, scientists think, might even harbour life. All gas giants have more or less visible rings orbiting around them, made of dust and chunks of rock or ice. Jupiter is the largest planet in our solar system.

Its diameter is roughly eleven times larger than the diameter of Earth. It has more than twice the mass of all other planets in the solar system combined. Jupiter’s core is made up of heavy elements and metallic hydrogen. It is surrounded by liquid hydrogen and gaseous hydrogen. About 90% of Jupiter's upper atmosphere is hydrogen, and 10% is helium, with trace amounts of methane, water vapour, ammonia and other compounds.

These trace elements give different colours to one of Jupiter's most prominent features — its clouds. The clouds form a pattern of horizontal stripes, parallel to Jupiter’s equator. Gases in Jupiter’s atmosphere move up and down, arranging the clouds into the patterns of darker belts and lighter zones. At the boundaries between belts and zones, large storms build, like whirlpools, resembling hurricanes on Earth. But unlike on Earth, these storms on Jupiter can last an extremely long time.

One of them, known as the Great Red Spot, has been observed for as long as 400 years! Saturn is slightly smaller than Jupiter. Its diameter is nine times bigger than Earth’s. In many ways, Saturn is very similar to Jupiter, but it has lower density. It’s actually the least dense planet in the solar system!

The clouds in Saturn’s outer atmosphere are thicker than in Jupiter’s, which makes the striped patterns less visible. Saturn is probably best known for its beautiful rings! They are made of dust and chunks of ice and they stretch for thousands of kilometers away from the planet, but are only a hundred meters thick! As of 2021, Saturn is believed to have the most moons of any of the planets in our solar system — more than eighty have been observed! Uranus and Neptune are much smaller than the other two gas giants.

They are sometimes called twin planets because they are very similar to each other in size, mass, and composition. Compared to Jupiter and Saturn, Uranus and Neptune contain more “ices.” These ices are water, ammonia and methane in a solid state. So, scientists sometimes classify these two planets as ice giants rather than gas giants. What makes Uranus unique is that its axis of rotation is not perpendicular to its orbit around the sun. Instead, the planet appears to be flipped on its side.

Its faintly visible bands of clouds run in the opposite direction than those of the other three giant planets. Neptune is slightly smaller than Uranus, but it has more mass, and it’s the densest giant planet in our solar system. Neptune's atmosphere has active and visible weather patterns, such as storms that appear as dark spots that come and go. Being so far away, the outer planets of our solar system are difficult to study, and scientists still have lots to discover.