Space is big. Like, really big. Most of us grew up staring at those classroom posters where the planets are all lined up like colorful marbles on a shelf, but the reality of the order of the planets closest to the sun is way more chaotic and fascinating than a flat piece of paper suggests. If you’re trying to remember if it’s Mars or Venus that comes first, or why we stopped counting Pluto (sorry, Pluto fans), you’ve come to the right place.
Basically, the solar system is divided into two main neighborhoods. You have the inner circle—the rocky, "terrestrial" planets—and then the outer suburbs where the gas giants live. It’s not just a random sequence; it’s a story of heat, gravity, and how the Sun basically blew all the gas away from the center billions of years ago.
Mercury: The Baked Rock
First up is Mercury. It’s the literal closest thing we have to the Sun, orbiting at an average distance of about 36 million miles ($58$ million kilometers). Because it’s so close, it zips around the Sun incredibly fast. One year on Mercury is only 88 Earth days. Imagine having a birthday every three months.
Mercury is tiny. It’s barely larger than our Moon. It’s also a land of extremes. Because it has almost no atmosphere to trap heat, the side facing the Sun gets roasted at 800°F (430°C), while the night side plunges to -290°F (-180°C). It’s honestly a brutal place to exist. NASA’s MESSENGER mission gave us the best look at this world, revealing a surface covered in craters and "wrinkles" called lobate scarps, which formed as the planet’s core cooled and the whole thing literally shrank.
Venus: Earth's Twisted Twin
Second in the order of the planets closest to the sun is Venus. On paper, it should be the "nice" planet. It’s almost exactly the same size as Earth. It’s made of similar stuff. But Venus is a nightmare.
While Mercury is closer to the heat source, Venus is actually the hottest planet in the solar system. Why? The Greenhouse Effect. Its atmosphere is a thick, choking blanket of carbon dioxide and clouds of sulfuric acid. This traps heat so effectively that surface temperatures stay around 900°F (475°C) day and night. That’s hot enough to melt lead. If you stood on Venus, you’d be simultaneously crushed by the pressure (90 times that of Earth), fried by the heat, and dissolved by the acid.
Scientists like Dr. Sara Seager have spent years looking at Venus as a cautionary tale for Earth. Even though it’s a hellscape, there’s been recent buzz about potential phosphine gas in its upper clouds, which could—maybe, possibly—hint at microbial life high up where the temperature is actually tolerable. But for now, it remains our toxic neighbor.
Earth: The Goldilocks Zone
Then there’s us. Third rock from the Sun. We live in what astronomers call the "Habitable Zone" or the "Goldilocks Zone." Not too hot, not too cold. Just right for liquid water to exist on the surface.
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We’re about 93 million miles away from the Sun. That distance is so fundamental to our existence that we call it one Astronomical Unit (AU). Everything else in space is measured against our distance from the Sun. Earth is unique in the order of the planets closest to the sun because it’s the only one we know for a fact has life. We have a protective magnetic field, a nitrogen-oxygen atmosphere, and a massive moon that keeps our tilt stable. Without that tilt, we wouldn't have seasons.
Mars: The Red Desert
Fourth is Mars. The "Red Planet." It’s about half the size of Earth and sits roughly 142 million miles away from the Sun.
Mars is where the "inner" solar system ends. It’s a cold, thin-aired desert. Most of the iron in its soil has literally rusted, which is why it looks red. We’ve sent a literal army of robots there—Curiosity, Perseverance, Zhurong—because Mars is the most likely place humans will visit next.
Why Mars Matters
People often ask why we're so obsessed with Mars instead of Venus. Simple: you can actually land on Mars without your spacecraft melting in seconds. It has ice at its poles, evidence of ancient riverbeds, and massive volcanoes like Olympus Mons, which is three times taller than Mount Everest. It’s a dead world now, but billions of years ago, it might have looked a lot like Earth.
The Big Gap: The Asteroid Belt
Before we hit the fifth planet, there’s a giant gap filled with millions of rocks. This is the Asteroid Belt. It’s not like the movies where Han Solo has to dodge boulders every two seconds; the space between asteroids is actually huge. But this belt acts as the border between the small, rocky planets and the giants.
Jupiter: The King of the Planets
Fifth in the order of the planets closest to the sun is Jupiter. This is where things get massive. Jupiter is so big that you could fit all the other planets in the solar system inside it—twice.
It’s a Gas Giant. There’s no solid surface to land on. If you tried to "land," you’d just sink through layers of hydrogen and helium until the pressure turned you into a diamond or something equally compressed. Jupiter is famous for the Great Red Spot, a storm bigger than Earth that has been raging for at least 300 years.
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Jupiter also acts as the solar system’s vacuum cleaner. Its massive gravity sucks in stray comets and asteroids that might otherwise head for Earth. We owe a lot to this giant ball of gas. It has over 90 moons, including Europa, which likely has a saltwater ocean hidden under its ice.
Saturn: The Lord of the Rings
Sixth is Saturn. It’s about 886 million miles from the Sun. While all the giant planets have rings, Saturn’s are the only ones you can see with a basic telescope from your backyard.
These rings aren’t solid. They’re made of billions of chunks of ice and rock, some as small as dust and others as big as mountains. Saturn is also incredibly light for its size; it’s mostly hydrogen and helium. If you had a bathtub big enough, Saturn would actually float in water.
Uranus: The Sideways Oddball
Seventh is Uranus. This is an "Ice Giant." It’s cold—really cold—and it’s a beautiful cyan color because of the methane in its atmosphere.
The weirdest thing about Uranus? It rotates on its side. Most planets spin like a top, but Uranus rolls like a bowling ball. Scientists think something the size of Earth smashed into it a long time ago and knocked it over. Because of this, its poles get 42 years of direct sunlight followed by 42 years of total darkness. Talk about seasonal depression.
Neptune: The Windiest World
Finally, the eighth planet: Neptune. It’s about 2.8 billion miles from the Sun. It takes 165 Earth years to complete just one orbit. Since it was discovered in 1846, it has only finished one single "Neptune year" and started its second.
Neptune is dark, cold, and whipped by supersonic winds. It’s nearly 30 times farther from the Sun than Earth is, so the Sun just looks like a particularly bright star in its sky. Like Uranus, it's an Ice Giant, but it’s a deeper, more vivid blue.
[Image comparing the sizes of the four gas and ice giants: Jupiter, Saturn, Uranus, and Neptune]
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What About Pluto?
Look, we have to talk about it. From 1930 to 2006, Pluto was the ninth planet. Then the International Astronomical Union (IAU) changed the rules. To be a planet, you have to:
- Orbit the Sun (Pluto does this).
- Be round (Pluto does this).
- Have "cleared the neighborhood" around your orbit.
Pluto failed the third one. It’s out in the Kuiper Belt, surrounded by thousands of other icy objects. If Pluto is a planet, then we’d have to call dozens of other things planets, too. So, Pluto was demoted to "Dwarf Planet." It’s still there, it’s still cool (literally), but it’s no longer in the main lineup of the order of the planets closest to the sun.
Common Misconceptions
People get a few things wrong when they think about the planetary order.
First, the distances are not even. The first four planets are relatively bunched together. Once you pass Mars, the distances between planets explode. The "inner" solar system is a tiny fraction of the total space.
Second, the "hottest" isn't the "closest." As we mentioned, Venus beats Mercury for the heat trophy because of its atmosphere.
Third, the planets don't stay in a straight line. They are constantly moving at different speeds in their orbits. Most of the time, they are on opposite sides of the Sun from each other.
Actionable Steps for Stargazing
If you want to see the order of the planets closest to the sun for yourself, you don’t need a NASA budget.
- Download a Sky Map App: Apps like Stellarium or SkyGuide use your phone’s GPS to show you exactly which "star" is actually Jupiter or Mars.
- Look for the "Steady" Light: Stars twinkle because of atmospheric turbulence. Planets generally don't. If you see a bright point of light that isn't flickering, it’s likely a planet.
- Venus and Mercury are "Twilight" Planets: Because they are closer to the Sun than we are, you’ll usually only see them near the horizon just after sunset or just before sunrise.
- Get a Pair of Binoculars: You don't need a $2,000 telescope to see Saturn's rings or Jupiter's four largest moons. A decent pair of bird-watching binoculars will actually show you the moons of Jupiter as tiny white dots.
Understanding the layout of our cosmic backyard helps put Earth in perspective. We’re a small, fragile rock tucked between a furnace and a frozen void, perfectly placed to exist.
To continue your journey into the cosmos, check out the live feeds from the James Webb Space Telescope or the NASA Eyes on the Solar System interactive map. These tools allow you to track the real-time positions of every planet and major moon in our system, providing a 3D view that no flat textbook could ever replicate. Start by identifying Venus in the evening sky this week; it's often the first "star" to appear and serves as a bright reminder of our place in the sequence.