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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.
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Q 01Who discovered Pluto in 1930?
Clyde Tombaugh
He was a 24-year-old self-taught farm boy from Kansas hired by Lowell Observatory to hunt for Planet X.
Q 02What device did Tombaugh use to spot Pluto moving between two photographic plates?
A blink comparator
Flicking rapidly between plates makes anything that has moved appear to jump.
Q 03Where was Pluto discovered?
Lowell Observatory, Flagstaff
Percival Lowell had founded it in 1894 and started the search for a ninth planet in 1906.
Q 04Who first suggested the name Pluto?
An 11-year-old English schoolgirl
Venetia Burney of Oxford proposed it to her grandfather over breakfast; he passed it to an astronomer who cabled Lowell.
Q 05The name Pluto had an extra attraction: its first two letters were the initials of whom?
Percival Lowell
The planetary symbol became a PL monogram, still used in astrology.
Q 06Pluto is named after the Roman god of what?
The underworld
The name is also an epithet of Hades, his Greek equivalent.
Q 07What was the Lowell staff's first-choice name for Pluto, rejected because an asteroid already had it?
Minerva
Minerva, Pluto and Cronus topped the list of over a thousand suggestions.
Q 08Which element was named after Pluto in 1941?
Plutonium
Glenn Seaborg followed the tradition of uranium and neptunium.
Q 09Which cartoon character was apparently named after the newly discovered Pluto in 1930?
Mickey Mouse's dog
Disney animator Ben Sharpsteen could never confirm exactly why the pup got the name.
Q 10In what year did the IAU redefine 'planet' and reclassify Pluto as a dwarf planet?
2006
Many planetary scientists still refuse to accept the demotion.
Q 11Which of the IAU's three planet criteria does Pluto fail?
Clearing the neighbourhood around its orbit
Its mass is only 0.07 times that of everything else in its orbit; Earth's is 1.7 million times.
Q 12The discovery of which more massive object in 2005 forced the debate over Pluto's status?
Eris
The press called it the tenth planet; the IAU instead made both it and Pluto dwarf planets.
Q 13What minor-planet number was Pluto given in 2006?
134340
Brian Marsden had suggested number 10000 in 1998; that idea was howled down.
Q 21What is Pluto's diameter?
About 2,377 km
That is a little bigger than Eris, though Eris is heavier.
Q 22Pluto's surface area is roughly the size of which country?
Russia
About 17.7 million square kilometres, slightly larger than Russia.
Q 23How many known moons does Pluto have?
Five
Charon plus the tiny Styx, Nix, Kerberos and Hydra.
Q 24Pluto's largest moon is so big that the pair are sometimes called what?
Q 14Pluto is a member of which region of the Solar System?
The Kuiper belt
It was the first Kuiper belt object found, six decades before the second.
Q 15How long does Pluto take to orbit the Sun?
About 248 years
It has not completed a single orbit since its discovery, and will not until 2178.
Q 16Between 1979 and 1999, where was Pluto relative to the eighth planet?
Closer to the Sun than Neptune
Its eccentric orbit dips inside Neptune's for about 20 years of each circuit.
Q 17Why can Pluto never collide with Neptune despite crossing inside its orbit?
A stable 3:2 orbital resonance keeps them apart
Pluto completes two orbits for every three of Neptune's, and objects sharing this rhythm are called plutinos.
Q 18Pluto's orbit is tilted to the plane of the planets by more than how much?
17°
Combined with its eccentricity, that sets it apart from the eight planets' near-circular, flat orbits.
Q 19How long does sunlight take to reach Pluto at its average distance?
About 5.5 hours
That is at 39.5 AU, roughly 5.9 billion km.
Q 20How does Pluto's mass compare with the Moon's?
About one-sixth
Its volume is about a third of the Moon's; it is less massive than seven moons in the Solar System.
A binary system (double dwarf planet)
Their centre of mass lies outside Pluto, and each keeps the same face to the other.
Q 25Who discovered Pluto's largest moon in 1978?
James Christy
He named it after his wife Charlene's nickname 'Char', dressed up to sound like the underworld ferryman.
Q 26Charon's discoverer named the moon partly after whom?
His wife Charlene
Which is why he pronounced it with a 'sh' sound, unlike the mythological ferryman.
Q 27What did the discovery of the largest moon finally allow astronomers to measure?
Pluto's mass
It came out at just 0.2% of Earth's, far too small to be Lowell's Planet X.
Q 28Which spacecraft flew past Pluto on 14 July 2015?
New Horizons
It had left Earth in 2006, when Pluto was still officially a planet.
Q 29What unusual cargo, honouring the 1930 discovery, rides aboard the Pluto flyby spacecraft?
Some of the discoverer's ashes
About 30 grams of Clyde Tombaugh's ashes are on board.
Q 30Which planet gave the Pluto probe a gravity assist in 2007?
Jupiter
The boost shaved years off the 3,462-day trip.