One of the four Jovian planets, Jupiter is the largest planet in the solar system. As a matter of fact, the giant planet is two-and-a-half times as massive as all the other planets in the solar system combined. Saturn, Uranus and Neptune are also giant planets and significantly larger than Earth.
For these reasons, the giant planets are referred to as gas giants, and they make up the Jovian planets in our solar system. We'll explain why they're so unique, but first let's talk about the solar system and the other planets within it.
Except Mercury, all terrestrial planets have significant atmospheres composed mostly of nitrogen and carbon dioxide. Earth's atmosphere, of course, also has a high amount of oxygen.
The gas giants include two of the outer planets of the solar system: Jupiter and Saturn. As the name implies, these are giant planets predominantly composed of hydrogen and helium. They lack solid surfaces and instead have a dense, rocky core enveloped by a thick atmosphere. Both planets have robust magnetic fields, complex ring systems and numerous moons.
The ice giants are the two planets of the outer solar system: Uranus and Neptune. Despite being commonly grouped with the gas giants, Uranus and Neptune are distinct because they have more atmospheric ice molecules, like water, ammonia and methane. Like their Jovian planet counterparts, Uranus and Neptune have many moons and ring systems, and their blue color sets them apart visually from the solar system's gas giants and other planets.
Jovian Planets vs. Terrestrial Planets
Terrestrial and Jovian planets differ primarily in terms of size, composition and physical characteristics. Terrestrial planets are smaller and have solid, rocky surfaces. They're composed predominantly of silicate rock and metal and they usually have a central core, a mantle and a crust. Their atmospheres are thinner compared to the Jovian planets, and they contain fewer moons.
In contrast, Jovian planets are much larger and don't have solid surfaces. Unlike terrestrial planets, they are composed mostly of hydrogen and helium, similar to the sun, and they have small cores surrounded by atmospheres with gaseous hydrogen and clouds.
Jovian planets have strong magnetic fields, numerous moons and some even have complex ring systems.
Jupiter's atmosphere is composed predominantly of molecular hydrogen and helium gas. Traces of other gases and compounds like methane, water vapor, ammonia and phosphine can also be found, contributing to the visible clouds and the planet's rich, banded appearance.
The outermost layer of Jupiter's atmosphere, the exosphere, is viciously cold with temperatures falling below minus 229 degrees Fahrenheit (minus 145 degrees Celsius). However, this gas giant has an outer layer that could be surrounded with a probable molten core of solid material with temperatures as hot as 90,032 degrees Fahrenheit (50,000 degrees Celsius).
The extreme temperature variation and the planet's rapid rotation causes massive storms patterns, including the Great Red Spot, a 190-year-old storm larger than terrestrial planet Earth.
Saturn's atmosphere, like Jupiter's, is composed primarily of hydrogen and helium, with trace amounts of other compounds such as ammonia, methane and water vapor. These elements interact with sunlight to create Saturn's banded, yellowish-brown appearance. Beneath the cloud layers, the temperature and pressure increase with depth, creating a hot core.
As for Saturn's rings, they're comprised mainly of countless particles of ice, with some rock and dust, ranging in size from tiny grains to massive chunks as big as mountains.
Despite their stunning appearance, Saturn's rings are remarkably thin, generally only about 32 feet (10 meters) thick.
Before the 1990s, Uranus was considered a gas giant like Neptune, Jupiter and Saturn. But Uranus' atmosphere is primarily made of gaseous hydrogen and helium, and it also contains a higher proportion of "ices" like water, ammonia and methane. So scientists coined an appropriate term for large planets like Uranus and Neptune: ice giants.
The temperature in the upper atmosphere of Uranus is typically about minus 371 degrees Fahrenheit (minus 224 degrees Celsius), making Uranus the coldest Jovian planet and coldest planet in the solar system.
Uranus has an extreme axial tilt of about 98 degrees, meaning the giant planet essentially orbits the sun on its side. This unusual orientation leads to extreme seasons on the planet, with each pole experiencing 42 years of continuous sunlight or darkness depending on its position in the planet's 84-Earth-year orbit around the sun.
Like Uranus, the planet Neptune was also once considered a gas giant until it was recognized with the ice giant planets. Neptune's atmosphere is composed mostly of hydrogen and helium, with traces of methane that give the planet its deep blue hue. The hydrogen compounds envelope its rocky core.
Despite its distance from the sun, the planet's atmosphere has the highest wind speeds in the solar system. Winds on the planet have been clocked faster than 1,200 miles per hour (2,000 kilometers per hour). To date, these are the fastest wind speeds on any planet recorded in the solar system.
Jovian Planet Moons
There are hundreds of moons around the outer planets that make up the Jovian planets. Saturn has the most moons, with 145 known satellites. Saturn's largest moon, Titan, has a thick atmosphere and liquid hydrocarbon lakes, making it one of the most Earth-like locations in the solar system.
Jupiter also has an impressive 92 known moons currently orbiting the gas giant, some larger than Earth's moon. Jupiter's largest four moons, Europa, Io, Ganymede and Callisto, are some of the biggest in the solar system.
Saturn, Uranus, and Neptune also have many moons. Uranus has 27 known moons, named after characters from the works of William Shakespeare and Alexander Pope, while Neptune has 14, the most intriguing of which is Triton. Triton is unique because it is the only large moon in the solar system with a retrograde orbit.
Gas Giants Outside the Solar System
The Jovian planets aren't the only four gas giants in the universe. Exoplanets — planets outside our solar system — also can be considered gas giants.
These gas giants are comparable in mass to Jupiter, but they orbit extraordinarily closely to their parent stars. This means hot Jupiters have very short orbital periods, usually less than 10 days. It also means a hot Jupiter has an extremely high surface temperature, often higher than 1,832 degrees Fahrenheit (1,000 degrees Celsius), hence the name "hot" Jupiter.
These giant planets also have tidally locked rotations. That means one side of the planet always faces the star, causing extreme temperature variations between the day and night sides of the planet. Hot Jupiters are the easiest of all exoplanets to detect by the Doppler technique because of their short orbital periods and large planetary masses.
Now That's Interesting
The Hubble Space Telescope has provided tons of data on the Jovian planets, including atmospheric changes, storm dynamics and impacts of comets. Observations of Saturn's ring system and seasonal changes, along with detailed imaging of Uranus and Neptune, have also greatly expanded our understanding of these outer planets. Data from the Hubble Space Telescope has been crucial to studying exoplanets, including Jovian-like gas giants, helping scientists define their existence in the broader universe.
This article was created in conjunction with AI technology, then fact-checked and edited by a HowStuffWorks editor.
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