Solar System Quiz: How Many Planets Can You Actually Name?
Spoiler: Most adults stop after Mars and start guessing.
Last updated: Aug 17, 2026
Read time: 7 min
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By Nibble Team
Nibble's Editorial Team
Our editorial team loves exploring how things work and why. We’re guided by the idea that people stay curious throughout their lives — they just need engaging stories and ideas to reignite that curiosity.
NASA says Jupiter is so massive that it could fit about 1,000 Earths inside it, and most people still couldn't pick it out of a lineup of planet photos. This Solar System quiz is built for exactly that gap: the stuff you learned once in a classroom and never touched again.
Consider this to be more of an informal gut check than a test of knowledge. The quiz is made up of 45 questions without the option for a grading curve or the presence of a teacher looking at you from above. After finishing the quiz, stay a while because the following section explains the facts that will confuse most people, which will lead to a correct impression about them.
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Quick recap: What's in our Solar System
Before the questions start, here's a fast refresher so you're not guessing blind.
- The Solar System quiz covers eight planets, not nine.
- Pluto was reclassified as a dwarf planet back in 2006.
- Mercury sits closest to the sun, but it isn't the hottest.
- Jupiter is the largest planet, roomy enough for 1,000 Earths.
- Moons, asteroids, and comets orbit alongside the eight planets.
- All eight planets orbit the sun inside the Milky Way galaxy, which is one of billions out there.
If any of this feels shaky, you're in good company. Curious why space itself looks pitch black even with a sun blazing nearby? Here's why space is black, and it isn't for the reason most people assume.
🪐 Want the full story behind these facts? Explore Space lessons on Nibble.
Take the Solar System quiz: 45 questions to test yourself
Grab a pen and paper, or keep score in your head. Each answer sits right below its question, so no scrolling is required.
- How many planets orbit the sun?
Answer: Eight.
2. Which planet sits closest to the sun?
Answer: Mercury.
3. Which planet is known as the red planet?
Answer: Mars, thanks to iron oxide, or rust, coating its surface.
4. What is the largest planet in the Solar System?
Answer: Jupiter.
5. What is the smallest planet?
Answer: Mercury.
6. Which planet has rings you can spot with a basic telescope?
Answer: Saturn.
7. Which planet spins on its side compared to the others?
Answer: Uranus.
8. Which planet is famous for its winds and deep blue color?
Answer: Neptune.
9. What is Pluto classified as today?
Answer: A dwarf planet.
10. Which planet is often called Earth's twin, even though it's nothing like Earth?
Answer: Venus.
11. What is the largest moon in the Solar System?
Answer: Ganymede, which orbits Jupiter.
12. Which two moons orbit Mars?
Answer: Phobos and Deimos.
13. What force keeps every planet locked in orbit around the sun?
Answer: Gravity.
14. Which planet hosts Olympus Mons, the largest volcano in the Solar System?
Answer: Mars.
15. Which planet has the most confirmed moons?
Answer: Saturn, with over 100 more than Jupiter.
16. What are the small icy bodies that grow tails when they near the sun?
Answer: Comets.
17. Which planet has a color that comes from methane in its atmosphere?
Answer: Uranus.
18. Roughly how many Earths could fit inside Jupiter?
Answer: About 1,000, according to NASA.
19. Which planet did astronomers reclassify in 2006?
Answer: Pluto.
20. Which planet is closest in size to Earth?
Answer: Venus.
21. Which planet is third from the sun?
Answer: Earth.
22. What is the band of rocky debris between Mars and Jupiter called?
Answer: The main asteroid belt.
23. About how many days does Earth take to orbit the sun once?
Answer: About 365 days.
24. Which planet has the shortest day?
Answer: Jupiter, at under 10 hours.
25. Which planet has the longest day?
Answer: Venus, where one day lasts longer than one year.
26. What is the name of Earth's only natural satellite?
Answer: The moon.
27. Which two planets have no moons at all?
Answer: Mercury and Venus.
28. What is the icy region beyond Neptune called?
Answer: The Kuiper Belt.
29. Which planet is known for its Great Red Spot?
Answer: Jupiter.
30. What makes Saturn's rings sparkle?
Answer: Ice and rock particles reflecting sunlight.
31. Which spacecraft became the first human-made object to leave the Solar System?
Answer: Voyager 1.
32. Which planet's surface pressure is strong enough to crush a submarine?
Answer: Venus.
33. What is a shooting star, really?
Answer: A meteor burning up in Earth's atmosphere.
34. Which planet's rings went undetected until 1977 because they're so faint?
Answer: Uranus.
35. Which planet is nicknamed the morning star or evening star?
Answer: Venus.
36. What is the coldest planet in the Solar System?
Answer: Uranus, even though Neptune sits farther from the sun.
37. Which planet takes the longest to orbit the sun?
Answer: Neptune, at about 165 Earth years.
38. Which planet was discovered through math before anyone spotted it with a telescope?
Answer: Neptune.
39. What are Saturn's rings mostly made of?
Answer: Ice and rock.
40. Which dwarf planet, besides Pluto, orbits inside the asteroid belt?
Answer: Ceres.
41. What do astronomers mean by "a year" on another planet?
Answer: The time it takes that planet to orbit the sun once.
42. Which planet has seasons most similar to Earth's, thanks to its axial tilt?
Answer: Mars.
43. What do we call the edge where the sun's influence gives way to interstellar space?
Answer: The heliopause.
44. Which planet has the most extreme temperature swings between day and night?
Answer: Mercury, since it has almost no atmosphere to hold in heat.
45. Which planet did Galileo first observe through a telescope in 1610, discovering four of its moons?
Answer: Jupiter.
Tally your score. If you landed all 45, you can probably skip the next section. Everyone else, keep reading.
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The questions that trip up almost everyone
A few of these questions catch nearly every reader, and the reasons why are more interesting than the facts themselves.
Take Venus and Mercury. Most people assume Mercury is the hottest planet because it is closest to the Sun, but Venus is hotter. Its thick atmosphere traps heat the way a lid traps steam on a pot, so the temperature never drops. Distance from the sun matters less than what surrounds a planet once you get there.
Pluto trips people up for a different reason. It isn't that people forget the planet exists. It's that muscle memory from grade school that still counts it as the ninth planet, even though the International Astronomical Union reclassified it as a dwarf planet back in 2006.
Then there's Ganymede. Plenty of quiz-takers confuse it for a planet since it's larger than Mercury. It's the largest moon in the Solar System, and it belongs to Jupiter, not the sun. Curious how the invisible pull that holds moons like Ganymede in place works? Here's how gravity works, explained without the physics-class jargon.
Common Solar System quiz mix-ups
| Common assumption | Actual fact |
|---|---|
| Mercury is the hottest planet | Venus runs hotter because of its thick, heat-trapping atmosphere |
| Pluto is the ninth planet | Pluto was reclassified as a dwarf planet in 2006 |
| Jupiter has the most moons | Saturn currently holds the record, with over 100 more confirmed moons |
| The sun is white | It looks white from space but appears yellow through Earth's atmosphere |
That last mix-up trips people up more than you'd think. If you want the full explanation, here's why the sun looks yellow instead of white once you're standing under Earth's atmosphere instead of floating in space.
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A quick way to keep the facts from slipping again
Here's the honest part: most people forget Solar System facts within weeks of taking a quiz like this one, simply because nothing brings the information back around. A single quiz creates a short spike in knowledge, then it fades the same way it did after your last science class.
Nibble's Space topic tackles that gap differently. Short lessons on planets, gravity, and stars show up in rotation, so facts resurface naturally instead of getting crammed once and dropped. The app's Trivia Quiz game format also lets you keep testing yourself the same way you did here, except as a two-minute habit instead of a one-time event.
If you liked how this quiz felt, more space trivia is waiting whenever you want another round.
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Your memory just failed re-entry: Nibble to the rescue
Taking a Solar System quiz is fun for five minutes. Remembering the answers takes small, repeated exposure instead of one big cram session, which is exactly what Nibble is built around.
Nibble is a knowledge app with over 670+ pieces of content across more than 35 topics, from Space and Biology to Philosophy and Personal Finance.
Inside the Space topic, you'll find short text lessons with interactive quizzes, one-minute videos, nearly ten-minute audio episodes for a commute, and the Trivia Quiz game format this article borrowed its structure from. You can even chat with the historical figures behind these discoveries, the same way you'd text a curious friend.
The app has over 10 million downloads across 170-plus countries and has earned "App of the Day" recognition in the US, the UK, Canada, Australia, and dozens of other countries. None of that matters if it doesn't fit your day, though, so lessons are built to run five to ten minutes, short enough for a coffee break or the wait before a meeting starts.
Curious how stars differ from planets, or why some shine brighter than others? These star facts make a solid next stop.
🪐 Turn today's quiz into tomorrow's habit. Keep learning about space on Nibble.
Frequently asked questions on the Solar System quiz
How many planets are in the Solar System?
Eight. Pluto used to make nine, but the International Astronomical Union reclassified it as a dwarf planet in 2006. If you grew up learning nine planets, you're not wrong; you're working from an older textbook. Today, the eight official planets are divided into rocky inner planets and gas or ice giants farther from the Sun.
What is the closest planet to the Sun?
Mercury comes in first, although it is the least hot planet in our universe. In terms of heat retention, Venus beats all planets this time thanks to its thick atmosphere. This is because Venus traps heat so effectively that its surface stays extremely hot even at night.
What is the largest planet in the Solar System?
Jupiter is without a doubt the largest planet in our Solar System, according to NASA's estimate of being able to hold more than 1000 planets similar to our Earth. With regards to speed of rotation, it is number one as well, being able to spin around itself in under 10 hours.
What is the largest moon in the Solar System?
Ganymede, which orbits Jupiter, takes that title. It's larger than the planet Mercury, which is exactly why it trips up so many people during a planet quiz for kids and adults alike. Its huge size makes Ganymede a fascinating reminder that not every moon is smaller than every planet.
Why isn't Pluto considered a planet anymore?
In 2006, the International Astronomical Union set new rules for what counts as a planet, including clearing its orbital path of debris. Pluto didn't meet that bar, so it became a dwarf planet instead. This change made Pluto one of the most famous examples of how scientific definitions can evolve as we learn more about our Solar System.
Which planet is known as the red planet?
Mars earns that nickname from iron oxide, or rust, covering its surface. It's also home to Olympus Mons, the largest volcano among the planets of the Solar System, standing nearly three times taller than Mount Everest — a scale that's hard to picture from Earth.
How many moons does Saturn have?
Saturn currently holds the record among the planets of our Solar System, with over 100 more confirmed moons than Jupiter. That number keeps climbing as telescopes improve, so don't be surprised if it rises again soon. Many of Saturn's moons are tiny, irregular objects, while a few are large enough to have their own fascinating features and landscapes.
What planet is closest to Earth in size?
Venus is known as Earth's twin due to its size, though this nickname cannot be applied further since it has very high surface temperatures and a poisonous atmosphere. In fact, its thick clouds trap heat, making Venus the hottest planet in the Solar System.
Published: Aug 17, 2026
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