Jupiter: Anatomy of a Gas Giant

Let's take a moment to talk about Jupiter's crazy proportions. The fifth planet from our sun has an equatorial diameter of about 89,000 miles (143,000 kilometers). Were Jupiter a hollow shell, you could cram more 1,300 Earths inside it. That makes it the largest planet in the solar system.

By the way, did you know that Jupiter has around 318 times the mass as Earth? As a matter of fact, the gas giant is two-and-a-half times as massive as all the other planets in the solar system combined.

Giant planet it is though, next to the sun Jupiter still looks puny. This familiar yellow star accounts for a staggering 99.8 percent of all the mass in the solar system — Jupiter included. Nevertheless, Jupiter is large enough to affect the sun in ways that Earth never could.

It's not quite accurate to say Jupiter orbits the sun's center like all the other planets. Instead Jupiter orbits a spot in empty space between it and the sun called the barycenter. Why? Because the sun doesn't just exert gravity on the massive planet; Jupiter is so big that it affects how the sun moves, too.

Now the size disparity between the sun and Earth is unbelievably vast. Because the relationship is so skewed, their shared barycenter is located within the sun itself. (After all, the sun's got way more mass.)

Ah, but Jupiter's a different story. Since the planet is so big, its barycenter with the sun resides outside of the star, at a point well above the solar surface. And here's another fun fact: Jupiter's gargantuan bulk gives the sun a slight — but noticeable — wobble. So if scientists ever detect that kind of tottering motion in a far-off star, it could mean that a Jupiter-sized planet is nearby.

Relative size isn't the only thing setting Earth and Jupiter apart. Compositionally, the two worlds are totally different. Mercury, Venus, Earth and Mars are all classified as terrestrial planets, meaning that they have hard outer surfaces and mostly consist of metals or silicate rocks.

On the other hand, Jupiter is the quintessential gas giant. A gas giant planet lacks a solid surface and outer crust and has an overwhelmingly gaseous atmosphere. For its part, Jupiter's two major ingredients are hydrogen and helium, though smaller quantities of methane, ammonia and water have also been detected.

Since it doesn't have a hard crust, scientists define Jupiter's "surface" as the outer level at which its atmospheric pressure equals that of Earth. Far below this external area, there's a layer dominated by molecular hydrogen. Beneath that, you'll find a level whose primary component is liquid metallic hydrogen. (A material reminiscent of the liquid mercury we find on Earth.)

The core at Jupiter's very center inspires much debate. Some astronomers have argued that it doesn't even exist and may have long since disappeared. Data collected by NASA's Juno spacecraft tells us the core is probably real, but we still don't know what it's made of. However, the thing does appear to be less condensed than Earth's iron and nickel-based inner core.

OK, so what's the deal with Jupiter's so-called surface? Well, if you look at the planet through a good telescope, you'll notice what look almost like stripes of color running across the planet.

Amazingly, neighboring swirls move in opposite directions. Astronomers call the darker ones "belts" while their lighter counterparts have been dubbed "zones."

Jupiter's stripes and swirls are windy clouds of ammonia and water floating in a gaseous atmosphere of hydrogen and helium. Variations in chemistry, transparency, shape and/or temperature might explain the color differences.

Tempests riddle the gas giant. South of Jupiter's equator in the Southern Hemisphere, there's a series of oval-shaped storms that rotate counterclockwise. Being whitish in coloration, these are nicknamed the "string of pearls." Since 1986, the exact number of "pearl" storms varied from six to nine, with eight being visible when the NASA Juno mission photographed the string Dec. 11, 2016.

Far better-known is the Great Red Spot. A giant storm with a crimson tint, it contains winds that swirl around at a rate of 270 miles per hour (434.5 kilometers per hour). Caught between two powerful jet streams — one to the east and one to the west — the spot hangs out at a latitude of 22 degrees below Jupiter's equator.

Although researchers think the giant storm may be shrinking, its current dimensions are still highly impressive. At 10,159 miles (16,350 kilometers) wide, the Great Red Spot is large enough to envelop our entire planet.

Astronomers have been keeping a constant eye on the storm since 1830. Therefore, we know, at minimum, the giant storm is more than 190 Earth years old. Its longevity may have something to do with Jupiter's rotation orbit.

Your hometown completes a new spin around Earth's axis once every 24 hours. But since Jupiter is largely gaseous, some of its latitudinal regions rotate faster than others do. At Jupiter's poles, a day lasts for 9 hours and 56 minutes. Meanwhile, places near Jupiter's equator see brisk, 9 hour and 50-minute days.

Still, no matter how you slice it, Jupiter has the shortest days of all the planets in this solar system.

Jupiter, Saturn, Uranus and Neptune are all Jovian planets. Jupiter is part of the Jovian system, which also includes Jupiter's rings and all of Jupiter's moons.

Yes, like Saturn and other planets with rings, Jupiter also has rings — albeit, less dramatic ones. NASA's Voyager 1 spacecraft discovered Jupiter's rings in 1979. The Jovian ring system comes in four major subsets, with the widest ring possessing an outer radius of about 140,429 miles (226,000 kilometers).

Data sent back by the Galileo spacecraft show that Jupiter's rings might have formed when dust from interplanetary meteoroids smashed into Jupiter's moons.

And speaking of moons, they're extremely common around Jupiter. No fewer than 92 known moons are currently orbiting the gas giant, some larger than Earth's moon. Jupiter's largest moon, Ganymede, is the biggest moon in the solar system and is larger than the planet Mercury.

Jupiter's four largest moons were the first moons discovered beyond Earth. These are the four Galilean moons and include Io, Europa, Ganymede and Callisto.

Five more of Jupiter's moons received official names in August 2019. Dubbed Pandia, Ersa, Eirene, Philophrosyne and Eupheme, the moons reflect a proud nomenclatural tradition. The planet Jupiter's namesake is the Roman god of lightning — and his counterpart in Greek mythology is the electrifying Olympian known as Zeus.