Pluto Trivia
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50 free Pluto trivia questions with answers — science & nature quiz, new questions added Aug 2026.
This Pluto trivia quiz covers the little world that was a planet for 76 years. It starts with the discovery: Lowell's hunt for Planet X, Clyde Tombaugh's year at the blink comparator, the Oxford schoolgirl who named it over breakfast, the PL monogram, Disney's dog and the element plutonium. Then the demotion: Eris, the IAU's 2006 definition, the neighbourhood Pluto never cleared, and the minor-planet number it got instead. The science section covers the 248-year tilted orbit that dips inside Neptune's, the 3:2 resonance that keeps them apart, a 6.4-day sideways spin, mass a sixth of the Moon's, Charon and the binary-planet barycentre, and what New Horizons found in 2015: the nitrogen-ice heart of Sputnik Planitia, water-ice mountains, a thin escaping atmosphere and hints of a buried ocean. Along the way come Triton's family resemblance, the plutinos, Tombaugh's ashes riding aboard the probe and the orbiter proposed for the discovery's centenary. Difficulty runs from easy to expert and is shown on each question, so it suits a classroom, a pub quiz or a space enthusiast. Every answer was checked against a reference page and each question carries its citation. Try our Planets and Solar System quizzes for more.
30 of 50 questions with answers and explanations. Play the quiz
Q 01Who discovered Pluto in 1930?
Clyde Tombaugh
Clyde Tombaugh was a Kansas farm boy with no degree who won his observatory job by sending in sketches of the planets made with a telescope he had built himself, and he was 24 when he found Pluto.
Q 02What device did Pluto's discoverer use to spot it shifting between two photographic plates?
A blink comparator
A blink comparator flips rapidly between two photographs of the same patch of sky, so the stars stay put while anything that has moved appears to jump back and forth.
Q 03Pluto was discovered in 1930 at an observatory in which US state?
Arizona
Arizona: Percival Lowell had built his observatory at Flagstaff in 1894 to study Mars, and its staff were still hunting his predicted 'Planet X' when Pluto turned up on their plates.
Q 04Who first suggested the name Pluto?
An 11-year-old English schoolgirl
An 11-year-old English schoolgirl, Venetia Burney of Oxford, offered the name over breakfast; her grandfather passed it to an astronomer friend, who cabled it to the discoverers in America.
Q 05Pluto's traditional planetary symbol is a monogram of which two letters?
P and L
P and L: they open the name Pluto and are also the initials of Percival Lowell, who began the hunt for a ninth planet, a coincidence that helped the name to win the observatory's vote.
Q 06Pluto is named after the Roman god of what?
The underworld
The underworld: Pluto was the Romans' name for the Greek Hades, and the dwarf planet's moons have since been named to match, from the ferryman of the dead to the three-headed guard dog.
Q 07Pluto's largest moon was found in 1978 when an astronomer noticed what on photographs of Pluto?
A bulge on one side
A bulge on one side: James Christy saw Pluto's image stretch and shrink in a regular rhythm, then found the same bump on plates taken years earlier, back to 1965.
Q 08Plutonium was named after Pluto in the 1940s; which chemical symbol did Glenn Seaborg give it as a joke?
Pu
Pu: Seaborg passed over the obvious 'Pl' for letters that sound like someone holding their nose at a stink, expecting to be overruled, but nobody got the joke and it went into the periodic table.
Q 09How is Pluto thought to have gained its family of moons?
A collision with another world
A collision with another world is the favoured answer: the moons' neat, circular orbits suggest they grew from the wreckage instead of being caught later, much as our own Moon is thought to have formed.
Q 10Which body voted in 2006 to strip Pluto of its status as the ninth planet?
International Astronomical Union
International Astronomical Union: the vote came at its meeting in Prague, and some planetary scientists, the Pluto mission's chief Alan Stern among them, rejected the result.
Q 11Which of the three official planet criteria does Pluto fail?
Clearing the neighbourhood around its orbit
Clearing the neighbourhood around its orbit is the test Pluto fails: it is round and it circles the Sun, but it shares its zone with a swarm of icy bodies that it is far too small to sweep up.
Q 12The discovery of which more massive object in 2005 forced the debate over Pluto's status?
Eris
Eris, hailed in the press as a tenth planet, was later named after the Greek goddess of discord, a fitting choice for the find that ended with Pluto and itself both classed as dwarf planets.
Q 13The American Dialect Society's word of the year for 2006 was 'plutoed'; what does it mean to be plutoed?
Q 21Which mountaineer has an ice mountain range on Pluto named after him?
Edmund Hillary
Edmund Hillary and Tenzing Norgay, the first to reach Everest's summit and return safely, each have a range, Hillary Montes and Tenzing Montes, because Pluto's official names honour pioneers of exploration.
Q 22Pluto's surface area is roughly the size of which country?
Russia
Russia is the nearest match: a globe 2,370 km across has about 17.7 million square kilometres of surface, yet the flyby found that small world crowded with mountains, glaciers and frozen plains.
Q 23Pluto's four small moons are Nix, Hydra, Kerberos and which other, named after a river of Greek myth?
Styx
To be demoted
To be demoted or devalued, as the ninth planet had been that August: the new verb beat 'climate canary' in the society's run-off vote.
Q 14Pluto is a member of which region of the Solar System?
The Kuiper belt
The Kuiper belt: Pluto was its first known member, and once a second turned up in 1992, followed by hundreds more, astronomers began to ask whether Pluto was a planet or simply one of a crowd.
Q 15How long does Pluto take to orbit the Sun?
About 248 years
About 248 years: Pluto has not yet finished a single lap since it was found in 1930 and will not complete its first until 2178.
Q 16For twenty years from 1979, Pluto's lopsided orbit put it where?
Closer to the Sun than Neptune
Closer to the Sun than Neptune: Pluto's stretched orbit dips inside Neptune's for about twenty years of each circuit, so through the 1980s and 1990s Neptune, not Pluto, was the outermost planet.
Q 17What keeps Pluto and Neptune from ever colliding, even over millions of years?
A 3:2 orbital resonance
A 3:2 orbital resonance: Neptune circles the Sun three times for every two circuits by Pluto, a rhythm that always keeps the pair billions of kilometres apart.
Q 18After its 2015 flyby, how long did the Pluto probe take to radio all of its stored data back home?
About 15 months
About 15 months: the probe recorded more than 50 gigabits during the flyby and then sent them home across more than five billion kilometres, the last arriving in October 2016.
Q 19How long does sunlight take to reach Pluto at its average distance?
About 5.5 hours
About 5.5 hours, because Pluto lies some 39 times farther from the Sun than we do; the same light reaches our own planet in roughly eight minutes.
Q 20How heavy is Pluto compared with our Moon?
About one-sixth
About one-sixth: the world once counted as the ninth planet is outweighed by seven moons of the Solar System, our own among them.
Styx, named for the river the dead had to cross, was the last of the four to be found, spotted in 2012 while astronomers checked the approaching probe's route for hazards.
Q 24Charon is so large beside Pluto that the two are often described as what?
A double planet
A double planet: Charon is half as wide as Pluto, so the pair's balance point lies in open space between them rather than inside Pluto itself.
Q 25Which telescope discovered all four of Pluto's small moons between 2005 and 2012?
Hubble Space Telescope
Hubble Space Telescope: it picked out Nix and Hydra in 2005 and two fainter moons in 2011 and 2012, during searches made to scout the way ahead for the approaching Pluto probe.
Q 26Charon's discoverer chose the name partly as a tribute to which member of his family?
His wife
His wife: Charlene Christy was 'Char' at home, so her husband proposed 'Charon' for the moon, and the mythical ferryman who shares the name made it fit Pluto's dark theme.
Q 27What did the discovery of the largest moon finally allow astronomers to measure?
Pluto's mass
Pluto's mass came out at about 0.2% of our own planet's, far too slight to have tugged the outer giants off course as the hunters of Planet X had supposed.
Q 28Which spacecraft flew past Pluto on 14 July 2015?
New Horizons
New Horizons was launched towards what was still the ninth planet; seven months into the flight astronomers reclassified its target as a dwarf planet.
Q 29What unusual cargo, honouring the 1930 discovery, rides aboard the Pluto flyby spacecraft?
Some of the discoverer's ashes
Some of the discoverer's ashes, about an ounce, ride in a small canister on the probe, and his 93-year-old widow, Patricia, was at the launch site to watch it leave.
Q 30Which planet gave the Pluto probe a gravity assist in 2007?
Jupiter
Jupiter's gravity flung the probe onward about 14,000 km/h faster, which cut three years off its journey to Pluto.