Solar System Facts

Ready to learn all about the planets, stars, moons and more featured in our Solar System puzzle? Read on!

The Sun

The center of our solar system: The Sun is a giant ball of hot plasma, mostly hydrogen and helium.
A nuclear powerhouse: It produces energy through nuclear fusion, keeping our planet warm and supporting life.
Our "big star": The Sun is about 109 times wider than Earth and makes up 99.8% of the solar system’s mass!

Mercury

Although Mercury is the closest planet to the Sun, it's NOT the hottest! Daytime temperatures reach 800°F (430°C), while nighttime drops to -290°F (-180°C)!

Also, Mercury zips around the Sun faster than any other planet—it completes one orbit in just 88 Earth days!

Distance from the Sun: Mercury moves in a stretched-out oval path around the Sun, so sometimes it’s much closer, and sometimes it’s much farther away.
- Closest approach (perihelion): About 28.6 million miles (or 46.0 million kilometers)
- Farthest distance (aphelion): About 43.4 million miles (or 69.8 million kilometers)
- Average distance: Roughly 36 million miles (or 57.9 million kilometers)
Distance from Earth: Mercury’s distance from Earth changes because both planets are zooming around the Sun at different speeds on different tracks!
- Closest approach (conjunction) is about 48 million miles (or 77 million kilometers)
- Farthest distance (opposition) is about 137 million miles (or 221 million kilometers),
- Average distance roughly 56 million miles (or 90 million kilometers)
Named for: The Roman messenger god (because Mercury moves so fast in the sky - at least from what we see on Earth!).
Number of Moons: None

Venus

Even though it’s not the closest to the Sun, Venus' thick atmosphere traps heat through a runaway greenhouse effect, making surface temperatures reach about 900°F (475°C)—hot enough to melt lead!

It takes 243 Earth days for Venus to rotate once on its axis, but only 225 Earth days to orbit the Sun. So if you lived there, the Sun would rise once a year—and set once a year!

Distance from the Sun: Venus goes around the Sun in a nearly perfect circle, but even a tiny stretch in its path makes it a little closer or farther at times.
- Closest approach (perihelion): About 66.8 million miles (or 107.5 million kilometers)
- Farthest distance (aphelion): About 67.7 million miles (or 108.9 million kilometers)
- Average distance: Roughly 67.2 million miles (or 108.2 million kilometers)
Distance from the Earth: Sometimes Venus is between us and the Sun (super close), and sometimes it’s on the far side of the Sun (really far), so the distance keeps changing.
- Closest approach (conjunction): About 25 million miles (or 40 million kilometers)
- Farthest distance (opposition): About 162 million miles (or 261 million kilometers)
- Average distance: Roughly 42 million miles (or 68 million kilometers)
Named for: The Roman goddess of love and beauty.
Number of Moons: None

Earth

About 71% of Earth's surface is covered in water, and our Moon helps control Earth's tides.

The Moon’s gravity pulls on Earth’s oceans, which causes the tides to rise and fall. When the Moon is overhead or on the opposite side of Earth, it creates high tides, and in between, we get low tides

Distance from the Sun: Earth’s path is a little squished, so we’re closest to the Sun in January and farthest away in July.
- Closest approach (perihelion): About 91.4 million miles (or 147.1 million kilometers)
- Farthest distance (aphelion): About 94.5 million miles (or 152.1 million kilometers)
- Average distance: Roughly 92.96 million miles (or 149.6 million kilometers)
Distance from the Earth: We live here! So Earth is always 0 miles from Earth 😊
Named for: The Old English word “Ertha” (meaning ground).
Number of moons: One

Mars

Known as the "Red Planet," Mars is covered in iron-rich dust (basically, rust!).

Mars is also home to Valles Marineris: an over 2,500 mile long canyon (that's about the width of the U.S.!) as well as Olympus Mons: The largest volcano in the solar system (3 times taller than Mount Everest!)

Distance from the Sun: Mars has a more oval-shaped orbit than Earth, so the distance between Mars and the Sun changes a lot during its year.
- Closest approach (perihelion): About 128.4 million miles (or 206.7 million kilometers)
- Farthest distance (aphelion): About 154.8 million miles (or 249.2 million kilometers)
- Average distance: Roughly 141.6 million miles (or 227.9 million kilometers)
Distance from the Earth: Mars and Earth race around the Sun at different speeds, so sometimes we’re close neighbors and other times we’re on opposite sides of the Sun.
- Closest approach (conjunction): About 34 million miles (or 55 million kilometers)
- Farthest distance (opposition): About 250 million miles (or 401 million kilometers)
- Average distance: Roughly 140 million miles (or 225 million kilometers)
Named for: The Roman god of war (because of its red color).
Number of moons: Two, Phobos & Deimos

Jupiter

Jupiter is the biggest planet in our Solar System. Over 1,300 Earths could fit inside!

It's also mostly made of gas - specifically hydrogen and helium (like a tiny star).
Jupiter also has a unique feature that we call "The Great Red Spot." It's a giant storm that has been raging for hundreds of years!

Distance from the Sun: Jupiter’s giant orbit is a little stretched out, which makes it closer to the Sun at one part of its journey and farther at another.
- Closest approach (perihelion): About 460.2 million miles (or 740.5 million kilometers)
- Farthest distance (aphelion): About 507.0 million miles (or 816.6 million kilometers)
- Average distance: Roughly 484 million miles (or 778.3 million kilometers)
Distance from the Earth: Jupiter is really far away, and since both Earth and Jupiter are moving in big circles around the Sun, the distance between us keeps changing.
- Closest approach (conjunction): About 365 million miles (or 588 million kilometers)
- Farthest distance (opposition): About 601 million miles (or 968 million kilometers)
- Average distance: Roughly 444 million miles (or 714 million kilometers)
Named for: The king of the Roman gods.
Number of Moons: 92+ moons, including Ganymede (the biggest moon in the solar system!), Europa, Callista and Io.

Saturn

Saturn has the biggest and brightest rings in the solar system! They're made of ice and rock and stretch out super far—way wider than the planet itself!

Saturn is the least dense planet in the solar system because it’s made mostly of hydrogen and helium—the same gases that make up stars. In fact, it could float in water (if you had a pool big enough!).

Distance from the Sun: Saturn takes almost 30 years to go around the Sun, and because its orbit isn’t a perfect circle, it has a closest and farthest point too.
- Closest approach (perihelion): About 926.6 million miles (or 1.491 billion kilometers)
- Farthest distance (aphelion): About 1.013 billion miles (or 1.638 billion kilometers)
- Average distance: Roughly 886 million miles (or 1.429 billion kilometers)
Distance from the Earth: Because Saturn takes almost 30 years to orbit the Sun, sometimes it’s on the same side as Earth—and sometimes it’s all the way across the solar system.
- Closest approach (conjunction): About 746 million miles (or 1.2 billion kilometers)
- Farthest distance (opposition): About 1.0 billion miles (or 1.67 billion kilometers)
- Average distance: Roughly 792 million miles (or 1.275 billion kilometers)
Named for: The Roman god of agriculture.
Moons: Over 146, including Titan, which has rivers and lakes of liquid methane! Our puzzle also features Enceladus, Tethys, Dione, Iapetus, Rhea, Hyperion, Phoebe and Mimas.

Uranus

Unlike other planets that spin like tops, Uranus is tilted over so far that it rolls like a ball as it orbits the Sun. Scientists think a giant space rock knocked it over long ago.

Uranus is an ice giant, with a mix of hydrogen, helium, and icy stuff like water, ammonia, and methane—which gives it its blue-green color. And even though it’s not the farthest planet, Uranus holds the record for the coldest atmosphere in the solar system—down to -371°F (-224°C)!

Distance from the Sun: Uranus goes around the Sun in a tilted, slightly squished circle, so its distance changes as it moves.
- Closest approach (perihelion): About 1.703 billion miles (or 2.741 billion kilometers)
- Farthest distance (aphelion): About 1.866 billion miles (or 3.004 billion kilometers)
- Average distance: Roughly 1.784 billion miles (or 2.871 billion kilometers)
Distance from the Earth: Uranus is super far and moves very slowly, so its distance from Earth depends on where both planets are in their long space journeys.
- Closest approach (conjunction): About 1.6 billion miles (or 2.6 billion kilometers)
- Farthest distance (opposition): About 1.98 billion miles (or 3.2 billion kilometers)
- Average distance: Roughly 1.7 billion miles (or 2.8 billion kilometers)
Named for: The Greek god of the sky.
Number of moons: 27+, including Miranda, which looks like it's been shattered and put back together. Our puzzle also features Umbriel, Oberon, Titania, Puck and Ariel.

Neptune

Neptune is the windiest planet in our solar system. Its storms can whip up winds faster than 1,200 miles per hour—that’s faster than a fighter jet!

Also, Neptune's bright blue color is the result of methane gas in its atmosphere. The methane absorbs red light and reflects blue, giving Neptune its beautiful ocean-like color.

And like Jupiter, Neptune also has a giant storm. It's called the Great Dark Spot, and it’s big enough to fit the whole Earth inside!

Distance from the Sun: Neptune’s path is almost a circle, but not quite — so it still has a nearest and farthest spot from the Sun.
- Closest approach (perihelion): About 2.771 billion miles (or 4.459 billion kilometers)
- Farthest distance (aphelion): About 2.817 billion miles (or 4.537 billion kilometers)
- Average distance: Roughly 2.798 billion miles (or 4.498 billion kilometers)
Distance from the Earth: Neptune is the farthest planet from the Sun, so when it and Earth are on the same side, it’s “closer,” and when they’re on opposite sides, it’s way farther!
- Closest approach (conjunction): About 2.7 billion miles (or 4.3 billion kilometers)
- Farthest distance (opposition): About 2.98 billion miles (or 4.8 billion kilometers)
- Average distance: Roughly 2.9 billion miles (or 4.7 billion kilometers)
Named for: The Roman god of the sea (because of its deep blue color).
Number of Moons: 14+, including Triton, which orbits backward compared to other moons. Our puzzle also features Nereid.

What about Pluto?

Pluto used to be the 9th planet, but in 2006, it was reclassified as a dwarf planet because it doesn’t clear its orbit.

What does "clearing its orbit" mean? When a planet clears its orbit, it means it has enough gravity to either:

Pull in,
Crash into, or
Fling away any other space rocks or debris near its path around the Sun.

So over time, the planet becomes the dominant object in its orbit.

Pluto shares its neighborhood with lots of other icy objects in the Kuiper Belt (a region beyond Neptune). It’s not big enough to clear them out, So it orbits the Sun alongside other similar-sized bodies instead of sweeping them away, as an actual planet would do.

Charon: Pluto’s Moon

What is Charon: Charon is the largest moon of Pluto and one of the biggest moons in the solar system compared to its planet. It’s so big relative to Pluto that they are sometimes called a double dwarf planet system!

Why Is Charon Special?

Charon is about 750 miles (1,207 km) wide—that’s half the size of Pluto, but still very large for a moon. Some scientists think Pluto-Charon should be called a double dwarf planet system rather than a planet and moon!

Because Charon is so big relative to Pluto, they orbit a point in space between them rather than Pluto being the center! We didn’t know what it looked like until 2015! NASA’s New Horizons spacecraft was the first to take close-up photos of Charon. 

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Supernovas: Cosmic Explosions

What is it? A supernova is a massive star’s grand finale—a gigantic explosion that outshines an entire galaxy for a short time!

How does it happen? When a huge star runs out of fuel, it collapses under its own gravity and kaboom!—a supernova!

Supernova leftovers: They create neutron stars (tiny but super dense stars) or black holes (gravity monsters).

The gold factory: Supernovas create gold, silver, and other heavy elements that end up in planets (and even in you!).

Blue Giants: The Biggest, Hottest Stars

What is it? A blue giant is a massive, super-hot star that burns through its fuel really fast.

Size matters: Some Blue Giants are hundreds of times bigger than the Sun!

Short but bright lives: While our Sun will last about 10 billion years, blue giants only live a few million years before exploding as supernovas.

Rigel (the brightest star in Orion) is a famous blue giant!

White Dwarfs: Stellar Leftovers

What is it? A white dwarf is the small, super-dense core left behind when a small- to medium-sized star (like our Sun) dies.

Tiny but mighty: A white dwarf is about the size of Earth but as heavy as the Sun!

No more fusion: White Dwarfs don’t produce energy anymore—they just slowly cools down for billions of years.

In about 5 billion years, our Sun will become a white dwarf!

Asteroids: Space Rocks

What is it? Asteroids are rocky leftovers from the early solar system.

Where are they? Most asteroids orbit in the Asteroid Belt between Mars and Jupiter.

Not round: Unlike planets, asteroids come in all shapes and sizes—some look like potatoes!

Biggest asteroid: Ceres (technically a dwarf planet) is 590 miles (950 km) wide!

Did an asteroid wipe out the dinosaurs? Yes! A 6-mile-wide asteroid hit Earth 66 million years ago, ending the age of dinosaurs.

Comets: Dirty Snowballs in Space

What is it? Comets are balls of ice, rock, and dust that orbit the Sun.

Famous for their tails! When comets get close to the Sun, the heat melts their ice, creating a glowing tail that can stretch millions of miles!

Where do they come from? Most come from the Kuiper Belt (near Pluto) or the Oort Cloud (way beyond Pluto).

One of the most famous for us on Earth, Halley’s Comet appears every 76 years—next visit in 2061!

Tell the difference: Comet or asteroid? Comets are icy, while asteroids are mostly rock and metal.

Black Holes: Gravity Monsters

What is it? A black hole is a region in space with gravity so strong that nothing—not even light—can escape!

How do they form? When a massive star collapses in a supernova, it creates a black hole.

Invisible but powerful: We can’t see black holes, but we detect them by how they pull on nearby stars and light.

Supermassive Black Holes are giant Black Holes live at the centers of galaxies, including the Milky Way’s Sagittarius A*. Even though it’s incredibly far away (About 26,500 light-years), Sagittarius A* helps hold the entire Milky Way galaxy together with its powerful gravity—including our solar system, which orbits the galactic center along with billions of other stars.

Planetary Nebula: The "Glowing Ghosts" of Dead Stars

What is it? A planetary nebula is a glowing cloud of gas and dust formed when a dying star sheds its outer layers. Despite the name, it has nothing to do with planets! Early astronomers thought these nebulae looked like planets through their telescopes—hence the misleading name.

How do they form? When a small- to medium-sized star (like our Sun) reaches the end of its life, it expands into a red giant. It then sheds its outer layers into space, forming a colorful gas cloud called a planetary nebula. The leftover core becomes a white dwarf, which emits ultraviolet light that makes the gas glow in brilliant colors. Over time, the nebula fades, leaving the white dwarf behind.

What’s Inside a Planetary Nebula? Glowing gas: Mostly hydrogen and helium, with traces of carbon, oxygen, and nitrogen. Different gases produce different colors:
Red → Hydrogen
Green → Oxygen
Blue → Helium
White Dwarf Core: At the center, a tiny but super-dense white dwarf keeps the nebula glowing.

Famous Planetary Nebulae include Ring Nebula (M57), that looks like a cosmic smoke ring and Helix Nebula, which is sometimes called the “Eye of God” because it looks like a giant eyeball. 

Protostar: A Baby Star in the Making

What is it? A protostar is a young, forming star that is still gathering material from a surrounding cloud of gas and dust. It's the earliest stage in a star’s life, before it becomes a full-fledged star like the Sun.

How do they form? A nebula (a massive cloud of gas and dust) begins to collapse under its own gravity. Gravity then pulls gas inward: The collapsing cloud forms a spinning, dense core—the protostar. As the protostar pulls in more gas, pressure and temperature increase, making it glow red. When the core gets hot enough (about 10 million°C!), nuclear fusion starts, turning hydrogen into helium. Finally, a new star is born! Once fusion is steady, the protostar officially becomes a main-sequence star (like the Sun).

How Long Does It Take for a Protostar to Become a Star?
Small stars (like the Sun): About 10 million years.
Huge stars (10x the Sun's size): Only 100,000 years!
Tiny stars (red dwarfs): Up to 100 million years!

Famous Protostars include the Orion Nebula, a giant stellar nursery (with hundreds of protostars forming right now) and T Tauri Stars, a type of young, unstable protostar that flares and flickers.

Supershells: Giant Bubbles in Space!

What is it? A supershell is a huge bubble-like structure in space, created by the combined effects of supernova explosions and stellar winds from massive stars. These cosmic bubbles are filled with hot, low-density gas and are often surrounded by denser shells of cooler gas and dust.

How do they form? First, massive stars pump out powerful stellar winds. These winds push gas outward, clearing a bubble around the stars. Then supernova explosions add to the blast! When stars reach the end of their lives and explode, they send out shock waves that expand the bubble even more. The surrounding gas gets compressed, creating a dense shell around the bubble, which can trigger the formation of new stars! Over time, these bubbles merge with others, forming gigantic cavities in galaxies.

How Big Are Supershells? They can be hundreds to thousands of light-years wide - some are so massive they stretch across entire regions of galaxies!

Where Can We Find Supershells? The Milky Way: Our galaxy has many supershells, often found near regions of active star formation. The Large Magellanic Cloud: This nearby dwarf galaxy has a famous supershell called LMC 4, one of the largest known! The Local Bubble: Our own Solar System is inside a fossil supershell! It was likely formed by supernova explosions millions of years ago.