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97 free Planets trivia questions with answers — science & nature quiz, new questions added Aug 2026.
50 free planets trivia questions with answers. Our solar system is home to scorching volcanoes on Io, methane lakes on Titan, and winds on Neptune that would make a hurricane look like a gentle breeze. Think you know your planets? These 97 questions will separate the stargazers from the true space experts.
30 of 97 questions with answers and explanations. Play the quiz
Q 01Which planet is nicknamed for its orange-red appearance?
Mars
The colour comes from iron oxide dust that coats much of the surface.
Q 02What is the largest planet in our solar system?
Jupiter
Jupiter is by far the largest planet in our solar system. It has a mass more than twice that of all the other planets combined and a diameter of about 142,984 km.
Q 03How many planets are in our solar system?
8
The IAU definition adopted in 2006 is what moved Pluto into the dwarf-planet category.
Q 04Which planet is closest to the Sun?
Mercury
Mercury orbits at an average distance of about 58 million km from the Sun, making it the closest planet. Despite this, Venus is actually hotter due to its thick greenhouse atmosphere.
Q 05Which planet has the most extensive ring system in the Solar System?
Saturn
The rings are mostly ice particles with a little rocky debris and dust.
Q 06What is the hottest planet in our solar system?
Venus
A crushing carbon dioxide atmosphere traps heat so well that Venus averages about 465°C (869°F) at the surface — hotter than Mercury, which sits closer to the Sun.
Q 07Which planet's rotation axis lies almost in the plane of its orbit, so it rolls around the Sun on its side?
Uranus
Uranus's tilt is 97.77 or 82.23 degrees depending on which pole you call north, so each pole gets 42 years of continuous sunlight.
Q 08What is the smallest planet in our solar system?
Mercury
Mercury is the smallest planet in our solar system with a diameter of about 4,880 km. Pluto, once considered the smallest planet, was reclassified as a dwarf planet in 2006.
Q 09Which planet is known as Earth's twin due to its similar size?
Venus
The resemblance ends at the surface, where a runaway greenhouse effect makes it the hottest planet.
Q 10Which planet has the Great Red Spot, a massive storm that has raged for centuries?
Jupiter
Jupiter's Great Red Spot is a persistent anticyclonic storm larger than Earth. It has been observed since at least 1831, and possibly since 1665, though it has been gradually shrinking in recent decades.
Q 11Which planet has the most moons in our solar system?
Saturn
Saturn holds the record for most known moons with over 140 confirmed natural satellites as of 2023. New moons continue to be discovered.
Q 12What is the name of the largest moon in our solar system?
Ganymede
Ganymede, a moon of Jupiter, is the largest moon in our solar system with a diameter of 5,268 km. It is even larger than the planet Mercury and is the only moon known to have its own magnetic field.
Q 13In which year did the IAU demote Pluto to dwarf planet?
2006
The IAU voted on 24 August 2006 in Prague to define 'planet' in a way that excluded Pluto; the American Dialect Society then made 'plutoed' its 2006 word of the year.
Q 21Which is the most massive known dwarf planet in the Solar System?
Eris
Pluto is slightly larger by diameter, but Eris outweighs it; it is also the largest known object never visited by a spacecraft.
Q 22Which NASA rover landed on Mars in February 2021?
Perseverance
Perseverance touched down in Jezero Crater, an ancient lake-delta site, on February 18, 2021, to drill and cache rock cores for a future Mars sample-return mission.
Q 23What is the name of the asteroid belt's only dwarf planet?
Ceres
Ceres is the only dwarf planet located in the asteroid belt between Mars and Jupiter. With a diameter of about 940 km, it is also the largest object in the asteroid belt, containing about a third of the belt's total mass.
Q 14Which planet has the shortest day (fastest rotation) in our solar system?
Jupiter
Jupiter has the shortest day of any planet, rotating once in just under 10 hours (9 hours 56 minutes). Despite being the largest planet, its rapid spin causes a noticeable bulge at its equator.
Q 15Which planet spins backward (retrograde rotation) compared to most other planets?
Venus
Venus rotates in the opposite direction to most planets (retrograde rotation), meaning the Sun rises in the west and sets in the east. A day on Venus (243 Earth days) is actually longer than its year (225 Earth days).
Q 16What is the farthest planet from the Sun in our solar system?
Neptune
Neptune is the farthest planet from the Sun at an average distance of about 4.5 billion km. Since Pluto was reclassified as a dwarf planet in 2006, Neptune holds this distinction.
Q 17Olympus Mons, roughly 2.5 times the height of Everest, is the tallest volcano on which planet?
Mars
It is roughly tied with Rheasilvia on the asteroid Vesta as the tallest mountain known in the Solar System.
Q 18Which moon of Saturn has a thick atmosphere and liquid methane lakes on its surface?
Titan
Titan is the only moon in our solar system with a dense atmosphere, which is primarily nitrogen with methane. The Cassini-Huygens mission revealed lakes and seas of liquid methane and ethane on its surface.
Q 19What are the four Galilean moons of Jupiter?
Io, Europa, Ganymede, Callisto
Io, Europa, Ganymede, Callisto are numbered I to IV outward from Jupiter; Galileo saw them in 1609–10, and no other Jovian moon was known until Amalthea in 1892.
Q 20Which planet has winds that can reach speeds of over 2,000 km/h, the fastest in the solar system?
Neptune
Neptune has the fastest winds in the solar system, with speeds exceeding 2,000 km/h (1,200 mph). This is remarkable given how far Neptune is from the Sun and how little solar energy it receives.
Q 24Which moon of Jupiter is considered the likeliest home for life elsewhere in our solar system?
Europa
Europa's smooth young surface points to a water ocean beneath the ice; sea salt on the surface suggests that ocean touches a rocky sea floor.
Q 25What is the densest planet in our solar system?
Earth
Earth averages 5.51 g/cm³ thanks to an iron-nickel core that makes up about a third of its mass.
Q 26Which planet did Urbain Le Verrier discover by calculation before it was observed?
Neptune
Neptune was predicted mathematically by Urbain Le Verrier in 1846 based on irregularities in Uranus's orbit. Johann Galle then observed it at the Berlin Observatory within 1 degree of Le Verrier's predicted position.
Q 27What is the main component of Jupiter's atmosphere?
Hydrogen
By mass the split is nearer 76% hydrogen and 24% helium, close to the composition of the Sun.
Q 28Which planet has the longest year (orbital period) in our solar system?
Neptune
Neptune has the longest orbital period of any planet, taking about 165 Earth years to complete one orbit around the Sun. It only completed its first full orbit since discovery in 2011.
Q 29What feature on Mars is the largest canyon system in the solar system?
Valles Marineris
Valles Marineris stretches over 4,000 km along the Martian equator, reaching depths of up to 7 km. It is roughly 10 times longer and 5 times deeper than the Grand Canyon on Earth.
Q 30Which spacecraft flew past both Uranus and Neptune?
Voyager 2
Voyager 2, launched in August 1977, flew past Uranus in January 1986 and Neptune in August 1989; no other spacecraft has visited either ice giant.