Space is big. You know that. But humans are actually terrible at visualizing just how massive the gap is between a "small" planet and a "big" one. When you look at a textbook diagram, the solar system planets and sizes are usually lined up like a neat row of marbles.
It's a lie.
If Earth were the size of a nickel, Jupiter would be about the size of a basketball. That’s a decent jump, right? But then you have to consider that the Sun—that glowing ball of plasma keeping us all alive—would be the size of a literal house. Most people realize Jupiter is big, but they don't grasp that you could fit 1,300 Earths inside it. It’s not just "larger." It’s a different league of existence.
The Rocky Inner Circle: Mercury to Mars
Let's start with the small stuff. Mercury is the runt of the litter. It’s barely larger than our Moon. In fact, if you put Mercury next to Ganymede (one of Jupiter's moons), Mercury actually loses the size contest. It has a diameter of about 3,030 miles. It’s basically a scorched, metal-heavy ball of rock that somehow hasn't been swallowed by the Sun yet.
Venus is Earth’s "twin," which is a bit of a misnomer. They are roughly the same size—Venus has a diameter of 7,521 miles compared to Earth’s 7,926—but that’s where the similarities end. Venus is a literal hellscape of sulfuric acid and crushing pressure. Earth is, well, home. We’re the "Goldilocks" planet, perfectly sized to hold onto an atmosphere without becoming a gas giant.
Then there’s Mars.
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People often think Mars is big because we talk about colonizing it so much. Honestly, it’s tiny. It’s about half the size of Earth. If you stood on Mars, you’d feel about 38% of Earth's gravity. Its diameter is only 4,212 miles. That’s roughly the distance from New York City to Rome. Imagine an entire planet with a surface area that isn't much larger than the total dry land on Earth.
The Gas Giants Change Everything
Everything changes once you cross the Asteroid Belt. This is where the solar system planets and sizes discussion gets truly weird.
Jupiter is the undisputed king. Its diameter is roughly 88,846 miles. It has a "Great Red Spot," which is a storm that has been raging for centuries, and that storm alone is bigger than Earth. Think about that for a second. A single weather pattern on Jupiter could swallow our entire world and still have room for a few Moons.
Saturn comes in second, with a diameter of about 74,897 miles. It’s famous for the rings, obviously. If you include the rings, the "size" of Saturn technically stretches out over 175,000 miles, but the planet itself is less dense than water. If you had a bathtub big enough, Saturn would float. It’s a giant, golden puffball of hydrogen and helium.
The Ice Giants: Neptune and Uranus
Then we have the "Ice Giants." Uranus and Neptune are often lumped together, but they’re distinct. Uranus is slightly larger in diameter (about 31,763 miles), while Neptune is actually more massive. Neptune is denser. It’s "heavier" in a gravitational sense.
- Uranus: 31,518 miles across.
- Neptune: 30,775 miles across.
- Earth (for scale): 7,917 miles.
These worlds are roughly four times the size of Earth. They are the middle children of the solar system—vastly bigger than us, but tiny compared to the giants like Jupiter.
Why the Standard Models Are Wrong
Every poster you bought at the Scholastic Book Fair as a kid was wrong. If you drew the planets to scale on a piece of paper, and Earth was a tiny dot, the distance between the planets would require a piece of paper miles long.
The solar system planets and sizes we see in media focus on the order, not the scale.
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The Sun contains 99.8% of the total mass in our solar system. Jupiter and Saturn take up most of what's left. Earth, Mars, and the rest are basically rounding errors in the grand math of the universe. It’s humbling. Or terrifying. Probably both.
Astronomer Mike Brown, famously known as the "man who killed Pluto," often talks about how our definition of a planet had to change precisely because of size. We started finding things in the Kuiper Belt (like Eris) that were roughly the same size as Pluto. If Pluto stayed a planet, we’d have to add dozens more. Size matters because it dictates gravity, and gravity dictates whether a celestial body can "clear its neighborhood" of debris.
The Volume vs. Mass Problem
One thing that trips people up is the difference between how big something looks and how much stuff is actually in it.
Earth is incredibly dense. We’re made of rock and metal. Jupiter is mostly gas. If you took the mass of all the other planets and combined them, Jupiter would still be twice as massive. It is the gravitational vacuum cleaner of our system. Without Jupiter’s massive size and gravity, Earth would likely be hit by way more asteroids than it currently is. Jupiter literally takes the hits for us.
Real-World Comparison Table (Converted to Prose)
To keep it simple:
Mercury is about 0.38 Earths wide.
Venus is 0.95 Earths wide.
Mars is 0.53 Earths wide.
Jupiter is 11.2 Earths wide.
Saturn is 9.4 Earths wide.
Uranus is 4.0 Earths wide.
Neptune is 3.8 Earths wide.
Misconceptions About the "Big" Planets
Is Jupiter the biggest thing in the universe? Not even close.
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In the context of solar system planets and sizes, Jupiter is the peak. But compared to other stars, it’s a pebble. There are stars like UY Scuti that are so large you could fit 5 billion Suns inside them.
Another common myth is that the gas giants don't have a "surface." While they are mostly gas, as you go deeper, the pressure turns that gas into liquid, and then potentially into a metallic solid. You can't "stand" on Jupiter, not just because there's no ground, but because the size of the atmosphere creates enough pressure to turn you into a puddle before you even got close to the core.
Exploring the Scale Yourself
If you want to actually feel the scale of the solar system planets and sizes, I highly recommend looking up the "If the Moon Were Only 1 Pixel" map online. It’s a scrollable map that shows the distance and size of the planets to scale. You will be scrolling for a long time. It really puts into perspective how much "nothing" there is between these massive bodies.
Actionable Ways to Use This Information
Knowing the scale of our neighborhood isn't just for trivia night. It changes how you look at the night sky.
- Grab a pair of 10x50 binoculars. You don't need a $2,000 telescope. With decent binoculars, you can see the moons of Jupiter. When you see those tiny dots, remember that each one is roughly the size of a planet like Mercury.
- Download a sky-mapping app. Use something like Stellarium or SkyGuide. Locate Saturn. When you see that yellowish "star," realize you're looking at a sphere nearly 10 times wider than the ground you're standing on.
- Visit a "Scale Model" walk. Many cities have them. The "Voyage Solar System" in Washington D.C. is a great example. Walking from the Sun to Pluto at a scale of 1 to 10 billion takes about 15 minutes. It’s the only way to truly "get" it.
The universe doesn't care about our ability to comprehend it. The sheer scale of the solar system planets and sizes is a reminder that we live on a very small, very fragile rock in a very large, very empty room. Understanding that scale is the first step in appreciating just how lucky we are to have an atmosphere that stays put and a Sun that stays the right distance away.
Check your local science center for star-gazing parties. Usually, there's a hobbyist with a massive Dobsonian telescope who would love to show you the rings of Saturn in real-time. Seeing it with your own eyes beats any textbook diagram.