Jupiter: 6 Facts About the Solar System's Biggest Planet

As an Amazon Associate, we earn from qualifying purchases. This post may contain affiliate links.

By Luis Gustavo. See how we research and review our content.

The fifth planet from the Sun and by far the largest of them all, Jupiter is a gas giant so massive it’s often described as “a star that almost made it” — its mass is enormous, but not quite enough to trigger the nuclear fusion that powers the Sun’s core. Visible to the naked eye as one of the brightest points in the night sky, Jupiter holds records and phenomena that were only understood in detail thanks to centuries of telescope observation and, more recently, spacecraft that have entered its orbit. These 6 facts gather some of the planet’s most impressive traits.

1. Jupiter is so big that more than 1,300 Earths could fit inside it

With a diameter of roughly 143,000 kilometers, Jupiter is so voluminous that, if it were hollow, it could hold more than 1,300 Earth-sized planets inside. Its mass is equally staggering: it’s about 2.5 times greater than the combined mass of all seven other planets in the Solar System put together. Despite that massive size, Jupiter is made mostly of hydrogen and helium, the same elements that make up stars, and it has no defined solid surface — a spacecraft attempting to “land” would simply sink deeper and deeper into the planet’s dense atmosphere, under ever-increasing pressure, and be crushed long before reaching any hypothetical rocky core. That combination of size and composition is why astronomers sometimes call Jupiter “the planet that almost became a second star” in the Solar System, even though its mass is still roughly 80 times too small to sustain nuclear fusion at its core.

2. The Great Red Spot is a storm that has lasted for centuries — and it’s shrinking

The Great Red Spot is a giant anticyclonic storm, visible as a reddish blotch in Jupiter’s southern hemisphere, documented in continuous telescopic observations since at least the 19th century — some astronomers point to possibly matching reports as far back as the 17th century. Winds inside the storm can exceed 400 km/h, and at its historical peak the spot was wide enough to fit three Earths side by side. More recent measurements, however, show the storm has been shrinking measurably for decades: today it’s estimated to be only about 1.3 times Earth’s diameter across, far smaller than records from a century ago. Scientists still debate whether that shrinking trend will continue until the storm dissipates entirely or whether it will stabilize at a new size, but the phenomenon keeps being tracked closely by ground-based telescopes and by the Juno spacecraft, which has orbited the planet since 2016.

3. Its four largest moons were discovered by Galileo in 1610 — and each one is a world of its own

Io, Europa, Ganymede, and Callisto, known as the Galilean moons after Galileo Galilei, who first observed them in January 1610, are among the most studied bodies in the outer Solar System. Io is the most volcanically active body known anywhere in the Solar System, with hundreds of active volcanoes fueled by constant gravitational stress from its closeness to Jupiter. Europa hides a liquid saltwater ocean beneath an icy crust that may hold more water than all of Earth’s oceans combined — which is why NASA’s Europa Clipper mission, launched in 2024, was sent specifically to study this moon in search of conditions compatible with life. Ganymede, meanwhile, is the largest moon in the entire Solar System, bigger even than the planet Mercury, and it’s the only known moon that generates its own magnetic field. Callisto, for its part, has one of the oldest and most heavily cratered surfaces ever observed, left nearly untouched by billions of years of impacts.

4. A day on Jupiter lasts less than 10 hours

Despite being the largest planet in the Solar System, Jupiter is also the fastest spinning one: a full rotation takes just under 10 hours, specifically about 9 hours and 56 minutes. That extreme rotation speed visibly flattens the planet’s poles and pushes its equator outward, giving Jupiter a slightly oval shape rather than a perfect sphere when viewed through powerful telescopes. The rapid rotation is also one of the forces behind the planet’s famous striped cloud bands: atmospheric jet streams travel in opposite directions in parallel bands around the equator, separating ammonia clouds into shades of white, orange, and brown that shift in appearance over the years as internal storms evolve.

5. Jupiter’s magnetic field is the strongest in the entire Solar System

Jupiter’s magnetic field is about 20,000 times stronger than Earth’s, the strongest of any planet in the Solar System, generated by an inner layer of metallic hydrogen that conducts electricity under immense pressure. That field creates permanent auroras at the planet’s poles, hundreds of times more intense than those seen on Earth, and it also produces radiation belts so intense that they pose one of the biggest engineering challenges for any spacecraft approaching Jupiter. The Juno spacecraft, for instance, had to be built with a shielded titanium “vault” to protect its most sensitive electronic components from the radiation, since prolonged direct exposure would quickly damage any conventional electronic equipment.

6. Jupiter’s gravity has deflected comets — and one even crashed into the planet in front of telescopes worldwide

Thanks to its enormous mass, Jupiter exerts a powerful gravitational pull on smaller objects crossing the inner Solar System, capable of bending the path of comets and asteroids — a role that, according to some models, may have helped reduce the frequency of impacts on Earth throughout the Solar System’s history, though scientists still debate how significant that “shield” effect really is in practice. The most dramatic, well-documented example happened in July 1994, when comet Shoemaker-Levy 9, already broken into more than 20 fragments by Jupiter’s own gravity during an earlier close pass, collided directly with the planet over the course of several days. The impact produced fireballs visible through amateur and professional telescopes around the world, along with dark scars in Jupiter’s atmosphere larger than Earth’s diameter that remained visible for months — one of the most closely observed astronomical events of the 20th century. Anyone who enjoys this kind of fact might also like our piece on facts about Saturn and facts about Mars, two other fascinating neighbors in our Solar System.