Size in space is a bit of a mind-melt. Honestly, most of those posters you saw in elementary school are lying to you. They show Jupiter sitting right next to Earth like a big marble next to a small one. In reality? If the Sun were a typical front door, Earth would be about the size of a nickel. Jupiter would be the size of a basketball. The scale is just... it's vast.
When we talk about the biggest objects in the solar system, we aren't just talking about planets. We’re talking about a star that holds 99.8% of everything, gas giants that could swallow thousands of Earths, and moons that are actually bigger than the planet Mercury.
Let's get one thing straight: the Sun is the only heavyweight that actually matters. Everything else—every planet, moon, asteroid, and stray piece of space dust—is basically the leftovers. It's the crumbs on the kitchen counter after the cake has been baked.
The Sun is the Undisputed King of Mass
If you want to understand the biggest objects in the solar system, you start and almost end with the Sun. It’s an G-type main-sequence star. Astronomers sometimes call it a "yellow dwarf," which is kind of a hilarious insult considering its scale.
The Sun is about 864,000 miles across.
📖 Related: Is Data Annotation a Legit Company? What Most People Get Wrong
Think about that. You could fit 1.3 million Earths inside it. It’s so massive that its gravity keeps objects in orbit billions of miles away, out in the Kuiper Belt and beyond. According to NASA’s Parker Solar Probe data, the Sun’s photosphere is where most of that visible light comes from, but the mass is concentrated in a core so dense that nuclear fusion is constantly screaming along at 15 million degrees Celsius.
It’s not just big. It’s the engine. Without its mass creating that gravitational well, the "system" part of the solar system wouldn't exist.
Jupiter: The Planet That Almost Was
Jupiter is the biggest "thing" that isn't the Sun. It has more than twice the mass of all the other planets combined. If you took Saturn, Neptune, Mars, and the rest and smashed them together, they still wouldn't come close to Jupiter’s bulk.
It’s a gas giant. This means it doesn't have a solid surface you could stand on. If you tried to land a ship, you’d just sink through layers of hydrogen and helium, getting crushed by the pressure until you became part of the metallic hydrogen soup near the center.
- Mass: 1,898 × 10^24 kg
- Diameter: 86,881 miles
- Fun fact: It spins so fast a day only lasts 10 hours.
The Great Red Spot is a storm that has been raging for at least 300 years. It’s shrinking now, but for a long time, that single storm was bigger than the entire Earth. That’s the kind of scale we’re dealing with. It’s a monster.
The "Lower" Heavyweights: Saturn and the Ice Giants
Saturn is the second largest, and obviously, it’s the one with the rings. But here’s the weird thing about Saturn: it’s incredibly light for its size. It’s mostly hydrogen and helium. If you had a bathtub big enough to hold it, Saturn would actually float.
The rings aren't solid. They are chunks of ice and rock, some as small as a grain of sand and others the size of a house. But even though the rings look massive, they are incredibly thin—maybe only 30 feet thick in most places.
Then you have Uranus and Neptune. These are the "Ice Giants."
They are bigger than Earth but way smaller than the big two. Neptune is actually denser than Uranus, even though Uranus is slightly larger in volume. This is the kind of nuance that gets lost in simple lists. Uranus is a weirdo because it rotates on its side. Imagine a planet rolling like a bowling ball around the Sun instead of spinning like a top.
When Moons Outgrow Planets
This is where the list of biggest objects in the solar system gets interesting. We usually think "Sun > Planets > Moons." But the universe doesn't like neat categories.
💡 You might also like: The Real Definition of the Light: Why It’s More Than Just Something You See
Ganymede, Jupiter’s largest moon, is actually larger than the planet Mercury.
If Ganymede orbited the Sun instead of Jupiter, we’d almost certainly call it a planet. It even has its own magnetic field. Titan, Saturn’s biggest moon, is also larger than Mercury. Titan is a bizarre world with a thick atmosphere and lakes of liquid methane. It’s a place where the "biggest" objects start to look like potential homes for future probes (or life).
- Ganymede (Moon of Jupiter) - 3,273 miles diameter
- Titan (Moon of Saturn) - 3,199 miles diameter
- Mercury (Planet) - 3,031 miles diameter
- Callisto (Moon of Jupiter) - 2,985 miles diameter
It’s a tight race at the bottom of the "huge" category.
Why Does Size Actually Matter?
It’s not just about bragging rights. Mass dictates everything in space.
Gravity is a function of mass. The reason we have a stable climate (mostly) and a predictable orbit is because the Sun is so much bigger than us. If Jupiter were significantly larger, it might have become a star itself, or at least a brown dwarf. If that had happened, our solar system would be a binary star system. Life on Earth probably wouldn't have happened in that chaos.
Mass also determines what a planet can hold onto. Mars is small, so it lost most of its atmosphere to space. Earth is big enough to keep its air. Jupiter is so big it keeps everything—even the light gases like hydrogen that smaller planets lose.
The Problem with "Big"
We also have to talk about the Oort Cloud.
If we define "objects" as structures, the Oort Cloud is the biggest thing by far. It’s a spherical shell of icy debris surrounding the solar system. It’s huge. It might extend a quarter of the way to the next star. But because it's mostly empty space with some rocks, we don't usually put it on the list of "objects."
Usually, people just want to know about the things they can see through a telescope.
Misconceptions About the Gas Giants
A lot of people think Jupiter and Saturn are just big clouds. Not really.
Deep down, the pressure is so intense that the hydrogen turns into a liquid metal. It conducts electricity. This is what creates Jupiter’s insane magnetic field, which is 20,000 times stronger than Earth’s. This field is so large that if it glowed in the dark, it would look several times larger than the full moon in our night sky, even though Jupiter is millions of miles away.
Size creates properties that smaller objects just don't have.
How to Visualize This for Yourself
If you really want to grasp the scale of the biggest objects in the solar system, go to a park with a soccer ball.
Place the soccer ball down; that’s the Sun.
Walk about 26 yards away. Drop a grain of salt. That’s Mercury.
Walk another 20 yards (46 total) and drop a peppercorn. That’s Venus.
Another 18 yards (64 total) and drop another peppercorn. That’s Earth.
To get to Jupiter, you’d have to walk about 330 yards from that soccer ball—over three football fields away. And Jupiter would only be the size of a grape.
The "bigness" of these objects is nothing compared to the "bigness" of the empty space between them.
Actionable Insights for Space Enthusiasts
If you want to move beyond just reading about these giants and actually experience the scale of the solar system, here is how you should proceed:
- Download a Real-Time Simulator: Use software like Stellarium or Eyes on the Solar System (NASA’s web tool). It allows you to toggle the "true scale" of objects, which shows you just how tiny Earth looks compared to the gas giants.
- Look for Conjunctions: Use an app like SkySafari to find out when Jupiter and Saturn are close to the Moon. Seeing Jupiter as a bright "star" next to our Moon helps you realize that even though it looks small, it's only because it's roughly 400 million miles away.
- Visit a Scale Model: If you are in the US, the Voyage Solar System Walk in Washington D.C. is a 1-to-10-billion scale model that stretches from the National Air and Space Museum to the Smithsonian Castle. It is the best way to feel the distance in your legs.
- Invest in 10x50 Binoculars: You don't need a $2,000 telescope to see the biggest objects. A decent pair of binoculars will let you see the four Galilean moons of Jupiter. Seeing those tiny dots move night to night is the best proof that these are massive, independent worlds.
The solar system is a hierarchy. It's a kingdom ruled by a star, policed by a massive gas giant, and filled with tiny rocky world's trying to stay out of the way. Understanding the scale isn't just a science fact—it’s a perspective shift. It makes our "big" problems feel a lot more manageable.