You’ve probably seen the posters. The ones where all the planets are lined up in a neat little row, looking roughly the same size so they fit on the page. It's a total lie. If we’re being honest, the solar system is basically just the Sun, a bunch of leftover dust, and one absolute unit of a planet: Jupiter.
When we talk about what’s the biggest planet in solar system, we aren't just talking about a "big" object. We’re talking about something so massive that it doesn't even orbit the center of the Sun. Instead, the Sun and Jupiter dance around a point in space just above the Sun's surface.
That’s some serious gravitational flex.
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Why Jupiter is the King of the Hill
Jupiter is huge. Like, "1,300 Earths could fit inside it" huge. If you took every other planet—Saturn, Neptune, even the "big" ones—and balled them together, Jupiter would still be twice as heavy. It’s the undisputed heavyweight champion of our neighborhood.
Most people think of it as a giant ball of gas, which is true, but it’s not just a cloud you could fly a plane through. The deeper you go, the weirder it gets. Thousands of miles down, the pressure is so intense that hydrogen gas turns into a liquid metal. This "metallic hydrogen" is what creates Jupiter's insane magnetic field, which is about 14 times stronger than Earth's.
The Great Red Spot is Shrinking (Kinda)
Everyone knows the Great Red Spot. It’s that iconic, swirling crimson eye that’s been raging for at least 300 years. But here’s the thing: it’s getting smaller.
Back in the 1800s, the storm was wide enough to fit three Earths side-by-side. Recent data from the Hubble Space Telescope and the Juno mission shows it’s now down to about one Earth’s diameter. It’s also getting taller as it gets narrower, like a piece of clay being squeezed. Astronomers aren't 100% sure if it’ll eventually disappear or just stabilize into a smaller circle.
The "Failed Star" Myth
You might’ve heard people call Jupiter a "failed star." It’s a catchy name, but it’s a bit of an exaggeration.
Jupiter is made of the same stuff as the Sun—mostly hydrogen and helium. If it had grown about 75 to 80 times more massive during the solar system's birth, it would’ve started fusing atoms and ignited into a second sun. But it didn't. It’s essentially a gas giant that just missed the cut for stardom.
A System of its Own: The 95 Moons
Calling Jupiter a planet almost feels like an understatement. It’s more like a mini-solar system. As of 2026, we’ve confirmed 95 moons orbiting the giant.
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The four "Galilean" moons—Io, Europa, Ganymede, and Callisto—are the real stars of the show:
- Ganymede: It’s actually bigger than the planet Mercury. If it orbited the Sun instead of Jupiter, we’d call it a planet.
- Io: The most volcanic place in the solar system. It’s basically a pizza-colored hellscape covered in sulfur.
- Europa: This one is the big deal for NASA. Under a thick crust of ice, there’s a salty liquid ocean that might actually hold life.
- Callisto: A quiet, crater-scarred world that hasn't changed much in billions of years.
Does Jupiter Actually Protect Earth?
There’s this long-standing idea that Jupiter is Earth’s "big brother," using its massive gravity to suck up dangerous asteroids before they hit us. Astronomers call it the "Jupiter Shield" theory.
The reality? It’s complicated.
While Jupiter definitely gobbles up some comets—like the famous Shoemaker-Levy 9 impact in 1994—its gravity also acts like a cosmic slingshot. Sometimes, it takes a rock that was minding its own business in the outer solar system and hurls it straight toward the inner planets. So, it’s just as likely to be a "sniper" as it is a "shield."
Exploring the Giant
We’re currently in a golden age of Jovian exploration. NASA’s Juno spacecraft is still up there, screaming past the planet in long, loopy orbits to avoid the fried-electronics-level radiation Jupiter puts out.
Looking ahead, the ESA’s JUICE (Jupiter Icy Moons Explorer) and NASA’s Europa Clipper are on their way. They aren't just looking for pretty pictures; they’re hunting for signs of habitability in those hidden subsurface oceans.
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What You Can Do Now
If you want to see what’s the biggest planet in solar system for yourself, you don’t need a billion-dollar probe.
- Look Up: Jupiter is one of the brightest objects in the night sky. It doesn't twinkle like a star; it shines with a steady, creamy light.
- Grab Binoculars: Even a cheap pair of 7x50 or 10x50 binoculars will reveal the four Galilean moons as tiny white dots flanking the planet.
- Use an App: Download a sky-tracking app like Stellarium or SkyGuide to pinpoint exactly where it is tonight based on your GPS.
- Follow the Missions: Keep an eye on the NASA Juno image gallery. They release raw data that amateur "citizen scientists" process into those mind-bending, swirling marble photos you see on social media.
Seeing that massive disk through a telescope for the first time is a rite of passage. It’s a humbling reminder that we’re living next door to a monster.