50 free Neptune trivia questions with answers — science & nature quiz, new questions added Aug 2026.
This Neptune trivia quiz is about the planet, the only one found by mathematics before anyone saw it. It opens with that story: Bouvard's tables, Adams and Le Verrier's rival calculations, Galle's discovery within a degree of the predicted spot, Galileo's near-miss in 1612, and the tussle over the name. Then the planet itself: 17 Earth masses, a 165-year orbit only completed once since discovery, supersonic winds, the Great Dark Spot that vanished, the Scooter, a lopsided magnetic field and a mysteriously hot thermosphere. Triton gets a section of its own: the backwards orbit that marks it as a captured Kuiper belt world, its nitrogen geysers, its record cold and its slow spiral to destruction. There are questions on Nereid's wild orbit, Proteus, the ring arcs named for the French motto, the Kuiper belt Neptune rules, and the twenty years when Pluto sneaked inside its orbit. Voyager 2's single 1989 visit, the four-hour signal delay and the death of Planet X round out the exploration, and the names, from sea king star to Rahab, finish it. Difficulty runs from easy to expert and is shown on each question, so it works for 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 01Where does Neptune rank in distance from the Sun?
Eighth
Since Pluto's 2006 demotion it has been the outermost planet, about 30 times farther from the Sun than Earth.
Q 02Neptune is unique among the planets in how it was found. How?
It was predicted mathematically before being seen
Wobbles in Uranus's orbit told Adams and Le Verrier where to look.
Q 03Who first observed Neptune through a telescope, on 23 September 1846?
Johann Gottfried Galle
He found it within a degree of Le Verrier's predicted position on the very night the letter arrived.
Q 04Which two mathematicians independently predicted Neptune's position from Uranus's orbit?
Adams and Le Verrier
A Franco-British row over credit followed; the consensus now is that both deserve it.
Q 05Whose 1821 tables of Uranus's orbit first revealed that something unknown was tugging on the planet?
Alexis Bouvard
His hypothesis of an unseen perturbing planet set Adams and Le Verrier to work after his death.
Q 06Which famous astronomer plotted Neptune as a 'fixed star' in 1612 and 1613 without realising what it was?
Galileo Galilei
It happened to be near Jupiter and had just turned retrograde, so it barely moved.
Q 07Neptune is named after the Roman god of what?
The sea
Le Verrier proposed the name, then tried to have the planet named after himself instead.
Q 08What does Neptune's astronomical symbol represent?
A trident
It is the three-pronged spear of the sea god.
Q 09Which name did Galle himself propose for the new planet?
Janus
Challis in England suggested Oceanus; Le Verrier briefly campaigned to name it after himself.
Q 10How long does Neptune take to orbit the Sun?
About 165 years
It only completed its first full orbit since discovery in July 2011.
Q 11In what year did Neptune complete its first full orbit since its discovery?
2011
It returned to the spot north-east of Iota Aquarii where Galle had first seen it.
Q 12Neptune's mass is about how many times Earth's?
17
That is only about a nineteenth of Jupiter, yet it is the densest of the giant planets.
Q 13Which planet has the fastest winds in the Solar System?
Neptune
They reach almost 600 m/s, over 2,000 km/h, faster than the speed of sound.
Q 14Roughly how fast are Neptune's strongest winds?
Q 21How long did radio signals take to travel from the spacecraft to Earth during the 1989 Neptune encounter?
246 minutes
Over four hours each way, so the flyby had to run on pre-planned commands.
Q 22The 1989 flyby's accurate measurement of Neptune's mass disproved which long-standing hypothesis?
An undiscovered Planet X tugging on the outer worlds
The mass came out 0.5% lower than calculated, which explained the leftover orbital wobbles.
Q 23What is Neptune's largest moon?
Triton
It holds more than 99.5% of all the mass in orbit around the planet.
About 2,200 km/h
Most of them blow in the opposite direction to the planet's rotation.
Q 15What was the huge storm photographed on Neptune in 1989 called?
The Great Dark Spot
It resembled Jupiter's Great Red Spot but had vanished by the time Hubble looked in 1994.
Q 16What had happened to the giant 1989 storm when Hubble looked for it in November 1994?
It had disappeared
A new dark storm had appeared in the northern hemisphere instead.
Q 17What nickname was given to a fast-moving white cloud group on Neptune seen before the 1989 encounter?
The Scooter
It zipped along faster than the Great Dark Spot; the Small Dark Spot was another 1989 storm.
Q 18What gives Neptune its blue colour?
Methane in its atmosphere
Voyager's images exaggerated the contrast, making it look far deeper blue than Uranus when the two are actually similar.
Q 19Neptune and Uranus are classed together as what type of planet?
Ice giants
They are smaller than Jupiter and Saturn and much richer in water, ammonia and methane.
Q 20Which is the only spacecraft to have visited Neptune?
Voyager 2
It made its closest approach on 25 August 1989, then dived past Triton because it was the last planet on its route.
Q 24Neptune's largest moon is unique among the big moons of the Solar System for what?
Orbiting backwards (retrograde)
That backwards orbit shows it was captured, probably a former dwarf planet from the Kuiper belt.
Q 25How soon after Neptune's discovery was its largest moon found by William Lassell?
17 days
None of the other moons were found by telescope until the 20th century.
Q 26What is the eventual fate of Neptune's largest moon as it slowly spirals inward?
To be torn apart into a ring
In roughly 28 billion years it will cross the Roche limit and be shredded.
Q 27What did the 1989 flyby see erupting from the surface of Neptune's largest moon?
Nitrogen geyser plumes up to 8 km high
That makes it one of the few worlds with active eruptions ever observed.
Q 28Neptune's largest moon, measured in 1989 as the Solar System's coldest known object, was roughly what temperature?
−235 °C
Its bright frozen-nitrogen surface reflects most of the feeble sunlight away.
Q 29How many known moons does Neptune have, according to the article?
16
Voyager 2 alone found six of them in 1989.
Q 30Which moon of Neptune has a highly eccentric orbit, its farthest point seven times its nearest?
Nereid
Its eccentricity is 0.75; it was the second Neptunian moon discovered.