Planets
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144 free Planets trivia questions with answers — science & nature quiz, new questions added Oct 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 144 questions will separate the stargazers from the true space experts.
30 of 144 questions with answers and explanations. Play the quiz
Q 01Mars looks red because its dust and rocks are coated in what?
Rust
Rust: iron in Martian rock and dust has oxidised, yet that same fine dust scatters light so that sunsets on Mars glow blue.
Q 02The five planets visible to the naked eye are named after gods from which mythology?
Roman
Roman: when Uranus was discovered, Johann Bode broke the pattern and named it after the Greek god of the sky.
Q 03Whose planetarium left out Pluto in 2000?
Neil deGrasse Tyson
Neil deGrasse Tyson: his Hayden Planetarium set Pluto apart from the planets years before astronomers demoted it, drawing angry letters from children that he retold in The Pluto Files.
Q 04In French and Spanish, which day of the week is named after Mercury?
Wednesday
Wednesday: French mercredi and Spanish miércoles both mean 'Mercury's day', but English swapped in Woden, a Germanic god equated with Mercury.
Q 05The word 'planet' comes from a Greek word meaning what?
Wanderer
Wanderer: ancient skywatchers saw planets drift from night to night against the fixed stars, so the Greeks called them wanderers.
Q 06Venus is hotter than Mercury, though farther from the Sun, mainly because of what?
Greenhouse effect
Greenhouse effect: Venus's thick carbon dioxide atmosphere traps so much heat that its surface, near 465 °C, is hot enough to melt lead.
Q 07What mainly causes Earth's seasons?
Its tilted axis
Its tilted axis: each hemisphere takes turns leaning toward the Sun, and Earth is actually closest to the Sun in January, during northern winter.
Q 08NASA lost the Mars Climate Orbiter in 1999 because its teams' software used different what?
Measuring units
Measuring units: ground software gave thrust figures in English units while the probe's software expected metric, so it flew too close to Mars and was lost.
Q 09Which Mars rover, built to last about 90 days, kept working for almost 15 years?
Opportunity
Opportunity: Martian winds kept sweeping dust off its solar panels, until a planet-wide dust storm in 2018 cut off its power for good.
Q 10What is the name of Jupiter's giant storm, wider than Earth?
Great Red Spot
Great Red Spot: it is shrinking, and by 2014 it was well under half the length observers measured in the late 1800s.
Q 11The habitable zone around a star, where life-friendly planets might exist, is nicknamed after which fairy-tale character?
Goldilocks
Goldilocks: like her porridge, planets in that zone are 'just right', neither too hot nor too cold, which makes them prime targets in the search for life.
Q 12What is the name of the largest moon in our solar system?
Ganymede
Ganymede: it is bigger than the planet Mercury, and Hubble's watch on its shifting auroras points to a salty ocean hidden beneath its icy crust.
Q 13Pluto lost planet status for failing which test?
Clearing its orbit
Clearing its orbit: Pluto is round and circles the Sun, but other objects cross its path, so it has not swept its neighbourhood clear.
Q 21Which 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 possible return to Earth by a later mission.
Q 22What is the name of the asteroid belt's only dwarf planet?
Ceres
Ceres: NASA's Dawn found that its bright spots are salt deposits, left where briny liquid seeped up from below and dried out.
Q 23Which moon of Jupiter is one of the most promising places to search for life beyond Earth?
Europa
Europa: its smooth, young crust hides an ocean that may touch a rocky seafloor, and NASA launched the Europa Clipper probe in 2024 to investigate.
Q 14Which astronomer's 1543 book placed the Sun, rather than Earth, at the centre of the universe?
Copernicus
Copernicus: the book appeared as he died, carrying an unsigned preface by Andreas Osiander that called the Sun-centred system merely a useful hypothesis.
Q 15Which NASA space telescope, launched in 2009, found thousands of planets by watching stars dim?
Kepler
Kepler: losing a second pointing wheel in 2013 ended its original survey, yet a reworked mission kept it finding planets until its fuel ran out in 2018.
Q 16Which astronomer suggested the 1990 'Pale Blue Dot' photo, which showed Earth as a speck about 6 billion km away?
Carl Sagan
Carl Sagan: he pushed for years to turn a probe's cameras back toward home, and he later named his 1994 book after the picture.
Q 17What distant shell of icy objects, thought to surround the Solar System, is a source of long-period comets?
Oort cloud
Oort cloud: it is so far away that it has never been imaged directly, so astronomers know it only through the comets thought to come from it.
Q 18Which moon of Saturn has a thick atmosphere and liquid methane lakes on its surface?
Titan
Titan: methane falls there as rain and fills rivers, lakes and seas, making it the only world besides Earth known to have liquid on its surface.
Q 19Which English word, taken from a planet's name, means cheerful and good-humoured?
Jovial
Jovial: it comes from Jove, another name for Jupiter, because astrologers believed people born under that planet were naturally merry.
Q 20Space probes gain speed by swinging close past a planet, a manoeuvre known as what?
Gravity assist
Gravity assist: the planet pays for the boost by losing a tiny, unmeasurable amount of its own orbital energy, while the probe gains a lot.
Q 24Venus, the only planet named after a female god, honours the goddess of what?
Love
Love: fittingly, most surface features on Venus are named after women from history and myth.
Q 25An 11-year-old Oxford schoolgirl suggested naming Pluto after the god of which realm?
The underworld
The underworld: Venetia Burney first put the idea to her grandfather, and astronomers adopted the name in 1930.
Q 26What is the main component of Jupiter's atmosphere?
Hydrogen
Hydrogen: deep inside Jupiter the pressure squeezes it into a liquid that conducts like metal, and that churning layer generates the planet's huge magnetic field.
Q 27Astronomer Percival Lowell was convinced that Mars was criss-crossed by what, built by intelligent beings?
Canals
Canals: spacecraft photos in the 1960s finally showed a cratered, barren world, and the straight lines turned out to be an optical illusion.
Q 28What feature on Mars is the largest canyon system in the solar system?
Valles Marineris
Valles Marineris: rather than being carved by a river, it likely formed as the Martian crust cracked apart and the canyon walls collapsed.
Q 29Which spacecraft flew past both Uranus and Neptune?
Voyager 2
Voyager 2: planners sent it on toward Uranus and Neptune only after its twin had completed its own mission at Saturn.
Q 30What phenomenon causes Io, Jupiter's moon, to be the most volcanically active body in the solar system?
Tidal heating
Tidal heating: Jupiter's gravity and the precisely timed tugs of two neighbouring moons keep flexing Io's interior, and that heat feeds hundreds of volcanoes.