Exoplanets Trivia
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50 free Exoplanets trivia questions with answers — science & nature quiz, new questions added Aug 2026.
Thirty years ago we knew of no planets beyond the Sun; now there are more than six thousand, including worlds that rain iron and glass, orbit two suns, or circle a dead star. This quiz covers the science of exoplanets: what counts as one, the 13-Jupiter-mass line, the letter-b naming rule, transits and the 80-parts-per-million dip, radial velocity, microlensing and direct imaging, the habitable zone and the one-in-five estimate for Sun-like stars. It also tells the discovery story: van Maanen's 1917 hint, van de Kamp's wobbles, Gamma Cephei, Wolszczan's pulsar planets, Mayor and Queloz and 51 Pegasi b, Osiris, Kepler's 150,000 stars, TESS, TRAPPIST-1's seven worlds, Proxima b, Kepler-186f, Earth 2.0, Tatooine-like Kepler-16b, Kepler-90's eight planets, K2-18b and its disputed biosignature, black WASP-12b, blue HD 189733 b, Methuselah, HR 8799 and rogue planets. Easy questions suit any space fan; the expert tier asks for catalogue numbers, discoverers and orbital periods. Every answer was checked against Wikipedia's articles on exoplanets, detection methods and the individual planets and missions, and the supporting sentence is attached to each question. If you like this, try our quizzes on the Solar System and on space telescopes.
30 of 50 questions with answers and explanations. Play the quiz
Q 01What is an exoplanet?
A planet outside the Solar System
A planet outside the Solar System is an exoplanet, from the Greek exo, 'outside'; surveys suggest the Milky Way holds at least one for every star, so planets probably outnumber the stars in the night sky.
Q 02Around what kind of object were the first confirmed exoplanets found in 1992?
A pulsar
A pulsar, the millisecond pulsar PSR B1257+12, hosts the first confirmed exoplanets: Aleksander Wolszczan and Dale Frail detected two planets in 1992 from tiny timing shifts in its radio pulses.
Q 03Which two astronomers announced 51 Pegasi b, the first exoplanet found around a Sun-like star?
Michel Mayor and Didier Queloz
Michel Mayor and Didier Queloz caught 51 Pegasi b from a French observatory in 1995 by timing shifts in its star's light; the find set off a planet-hunting boom that has since turned up thousands more worlds.
Q 04Which name, Latin for 'half', did the IAU give 51 Pegasi b?
Dimidium
Dimidium, Latin for 'half', points to a mass about half that of Jupiter; it won the IAU's 2015 public naming vote, which also renamed the planet's star Helvetios.
Q 0551 Pegasi b is the prototype of which class of exoplanet?
Hot Jupiters
Hot Jupiters are gas giants that whip around their stars in days; 51 Pegasi b upset the old view that giants stay far out, and astronomers still debate whether such planets formed close in or migrated inward.
Q 06Which three names did the IAU give the planets of the neutron star PSR B1257+12, itself renamed Lich?
Draugr, Poltergeist and Phobetor
Draugr, Poltergeist and Phobetor, a Norse undead, a noisy ghost and a dream-haunter from Ovid, won the IAU's 2015 public vote because the planets circle the corpse of a star, renamed Lich after an undead sorcerer.
Q 07Which French-led space telescope, launched in 2006, began hunting transiting planets over two years before Kepler?
CoRoT
CoRoT was the first spacecraft dedicated to finding planets by their transits; it caught its first within three months of starting observations in 2007, and two years later found the first planet shown to be rocky.
Q 08Which two methods have discovered the most exoplanets?
Transit photometry and Doppler spectroscopy
Transit photometry and Doppler spectroscopy account for the great majority of confirmed exoplanets; the transit dip reveals a planet's size, the shifting stellar spectrum its minimum mass, and both favour large planets close to their stars.
Q 09An Earth-sized planet crossing a Sun-like star dims its light by roughly what share?
About 0.01%
About 0.01% is all the light an Earth-sized planet blocks, because its disc covers roughly one twelve-thousandth of the star's; catching so slight a dip took a space telescope above the blur of the atmosphere.
Q 10Which space telescope detected carbon dioxide in the atmosphere of the exoplanet WASP-39 b in 2022?
James Webb Space Telescope
James Webb Space Telescope caught the gas's fingerprint in starlight filtered through the air of WASP-39 b, a puffy gas giant 700 light-years away, during its very first weeks of science work.
Q 11The radial velocity method detects a planet by measuring what?
The star's small orbital wobble
The star's small orbital wobble shows up as a rhythmic Doppler shift in its light; the planet at Proxima Centauri moves its star at only walking pace, about 5 kilometres an hour, which is why the method needs superb spectrographs.
Q 12Which planet-finding method relies on a nearer star briefly magnifying the light of a far more distant one?
Gravitational microlensing
Gravitational microlensing happens when two stars line up by chance as seen from Earth: the nearer one bends and magnifies the farther one's light like a natural lens, and a planet circling it adds a brief extra flash.
Q 13The IAU's working mass limit for a planet, about 13 Jupiters, marks where an object can fuse what?
Q 21NASA's Kepler telescope, launched in 2009, honours a 17th-century astronomer famous for his three laws of what?
Planetary motion
Planetary motion: Johannes Kepler showed in the early 1600s that planets move in ellipses, not perfect circles, and the telescope named after him leaned on his laws to turn repeating dips in starlight into orbits.
Q 22About how many stars did Kepler monitor at once in its fixed field of view?
150,000
150,000 stars were watched at once, out of about half a million in view, because a planet crosses its star's face only if its orbit happens to be seen edge-on, so most systems show nothing at all.
Q 23Why was Kepler retired in October 2018?
Its fuel ran out
Deuterium
Deuterium, a heavy form of hydrogen, fuses at lower temperatures than the ordinary kind, so anything massive enough to burn it, from about 13 Jupiters up, is no longer counted as a planet.
Q 14The first exoplanet found in a system is lettered 'b'; what counts as 'a'?
The host star
The host star counts as 'a', so the first planet found takes b and later finds take c, d and so on in order of discovery, not distance; a system's b can orbit farther out than its c.
Q 15How far away are the nearest known exoplanets, which orbit Proxima Centauri?
4.2 light-years
Proxima Centauri, 4.2 light-years away, is the Sun's nearest neighbour, close enough that a 2016 plan imagined laser-driven light sails making the trip in about 20 years at a fifth of light speed; by 2025 that project was on hold.
Q 16Proxima Centauri b hugs its dim star so closely that one of its years lasts about how long?
About 11.2 days
About 11.2 days is all Proxima Centauri b needs for one orbit, twenty times closer in than Earth is to the Sun; yet the star is so faint that this tight orbit still sits in the habitable zone.
Q 17What term describes a planet that always shows the same face to its star, as the Moon does to Earth?
Tidally locked
Tidally locked planets turn exactly once per orbit, which leaves one side in endless day and the other in endless night; worlds that orbit close to small, dim stars are expected to end up this way.
Q 18How many known planets orbit the ultra-cool red dwarf TRAPPIST-1?
Seven
Seven Earth-sized planets circle TRAPPIST-1 so tightly that all their orbits would fit inside Mercury's; from the surface of one, its neighbours could at times loom larger than the Moon does in our sky.
Q 19The Belgian telescope behind TRAPPIST-1 has an acronym chosen to honour which national speciality?
Monastery-brewed beer
Monastery-brewed beer, in the shape of Belgium's Trappist ales, gave the telescope its name: the Liège astronomers bent 'Transiting Planets and Planetesimals Small Telescope' into an acronym to flag the project's Belgian roots.
Q 20HD 209458 b, a planet caught losing its atmosphere to space, is nicknamed after which Egyptian god?
Osiris
Osiris, in the telling the astronomers cited, was cut to pieces by his brother, a fit for a planet that Hubble found in 2003 to be shedding its hydrogen atmosphere into space.
Its fuel ran out: with the last hydrazine spent, Kepler could no longer point precisely, and NASA retired it on 30 October 2018 after nine and a half years and more than 2,600 confirmed planets.
Q 24What was the first Earth-radius planet found in another star's habitable zone?
Kepler-186f
Kepler-186f, found in 2014, gets only a third of the starlight Earth does: on this world, which circles a red dwarf every 130 days, high noon would look about as bright as an hour before sunset here.
Q 25Which planet, announced in July 2015, was nicknamed 'Earth 2.0' or 'Earth's Cousin'?
Kepler-452b
Kepler-452b takes 385 days to circle a Sun-like star and is about 60 per cent wider than Earth, which earned the nickname; a 2018 reanalysis questioned whether its faint transit signal was real at all.
Q 26Kepler-16b, nicknamed Tatooine, was the first transiting example of what kind of world?
One orbiting two stars at once
One orbiting two stars at once: Kepler-16b would see double sunsets like Luke Skywalker's home in Star Wars, but it is a cold, Saturn-sized world of gas rather than a desert.
Q 27Kepler-90's eighth planet, tying the Solar System's tally, was found in old data in 2017 by what?
A Google neural network
A Google neural network, trained on 15,000 signals that people had already checked, combed 670 star systems and caught the faint transits of Kepler-90i that earlier searches had missed.
Q 28After a second reaction wheel failed in 2013, Kepler was kept steady for its K2 mission by the pressure of what?
Sunlight
Sunlight pressing evenly on the spacecraft stood in for the lost wheel: engineers balanced Kepler against it, a trick NASA likened to a kayak steering into the current, and won four more years of planet hunting.
Q 29Which satellite, launched on a Falcon 9 in April 2018, surveys 85% of the sky for transiting planets?
TESS
TESS, the Transiting Exoplanet Survey Satellite, concentrates on the nearest and brightest stars, so the planets it finds are close enough for other telescopes to weigh them and study their atmospheres.
Q 30Which planet is the best-known candidate 'hycean' world, with a possible ocean beneath a hydrogen-rich atmosphere?
K2-18b
K2-18b, a sub-Neptune in its star's habitable zone, became the poster child for 'hycean' worlds when 2023 spectra showed methane and carbon dioxide; a 2025 claim of a gas linked to life there was soon disputed.