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; the word combines the Greek prefix exo-, 'outside', with planet, and thousands have been confirmed since the first discoveries in the 1990s.
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 the first exoplanet around a Sun-like star, 51 Pegasi b, in October 1995?
Michel Mayor and Didier Queloz
Michel Mayor and Didier Queloz of the University of Geneva made the detection with the ELODIE spectrograph at the Observatoire de Haute-Provence and shared the 2019 Nobel Prize for it.
Q 04What official proper name did the IAU give 51 Pegasi b?
Dimidium
Dimidium, chosen in the IAU's 2015 NameExoWorlds vote, is Latin for 'half', a nod to the planet's minimum mass of about half that of Jupiter; its star became Helvetios.
Q 0551 Pegasi b is the prototype of which class of exoplanet?
Hot Jupiters
Hot Jupiters are gas giants orbiting scorchingly close to their stars, typically in under ten days; 51 Pegasi b, which circles its star in about four days, was the first found.
Q 06What are the names of the three planets orbiting the neutron star PSR B1257+12?
Draugr, Poltergeist and Phobetor
Draugr, Poltergeist and Phobetor were chosen in the IAU's 2015 naming contest for the three planets, while the star itself became Lich; the names come from undead and nightmare lore.
Q 07Which was the first space telescope designed to find exoplanets by the transit method?
CoRoT
CoRoT, a French-led mission launched in December 2006, was the first space telescope designed to hunt transiting exoplanets, staring at star fields for months at a time, years before Kepler.
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 transiting a Sun-like star dims it by roughly how much?
80 parts per million
Roughly 80 parts per million: the dip equals the ratio of the planet's disc area to the star's, and Earth's radius is only about 1/109 of the Sun's, so the drop is 0.008 per cent.
Q 10What was the first exoplanet discovered by the transit method, in 2002?
OGLE-TR-56b
OGLE-TR-56b, a giant planet flagged by the OGLE survey in 2002 and confirmed by follow-up spectroscopy, was the first planet found by its transits; HD 209458 b had been seen transiting in 1999 but was discovered by radial velocity.
Q 11The radial velocity method detects a planet by measuring what?
The star's small orbital wobble
The star's small orbital wobble, as it circles the system's centre of mass, shifts its spectral lines back and forth by the Doppler effect; 51 Pegasi's wobble is only about 50 metres per second.
Q 12Which detection method uses a star's gravity to magnify a distant background star?
Gravitational microlensing
Gravitational microlensing briefly brightens a background star when a foreground star passes in front, and a planet around the lens adds a short extra spike; OGLE-2005-BLG-390Lb was an early find.
Q 13What is the IAU's working mass limit separating planets from brown dwarfs?
Q 21In which year did NASA launch the Kepler space telescope?
2009
NASA launched Kepler on 7 March 2009 aboard a Delta II rocket from Cape Canaveral, sending it into an Earth-trailing solar orbit to stare at a single patch of sky in Cygnus and Lyra.
Q 22Approximately how many stars did Kepler continually monitor in its fixed field of view?
150,000
150,000 stars, selected from the roughly half a million in its 115-square-degree field in Cygnus and Lyra, were monitored by Kepler's single photometer every 30 minutes for brightness dips.
Q 23Why was Kepler retired in October 2018?
Its fuel ran out
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.
13 times Jupiter
13 times Jupiter is the mass at which an object of solar composition can fuse deuterium; the IAU's working definition draws the planet boundary there, with 80 Jupiters the hydrogen-burning limit for stars.
Q 14By convention, the first planet discovered around a star gets which letter?
b
The letter b goes to the first planet found, because the star itself is treated as component 'a'; later planets get c, d and so on in order of discovery, not distance.
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 stellar neighbour, a faint red dwarf in the Alpha Centauri system; its planet Proxima b was announced in August 2016.
Q 16What is the orbital period of Proxima Centauri b?
About 11.2 days
About 11.2 days is the orbital period of Proxima Centauri b, which circles its star at just 0.05 AU, yet the red dwarf is so dim that this still lies in the habitable zone.
Q 17Who led the team that announced Proxima Centauri b in 2016?
Guillem Anglada-Escudé
Guillem Anglada-Escudé of Queen Mary University of London led the Pale Red Dot campaign, which used the HARPS spectrograph to nail down a Doppler signal suspected in earlier data.
Q 18How many known planets orbit the ultra-cool red dwarf TRAPPIST-1?
Seven
Seven Earth-sized planets circle TRAPPIST-1 with periods from 1.5 to 19 days, three of them in the habitable zone; the ultracool dwarf lies about 40 light-years away in Aquarius.
Q 19TRAPPIST-1 takes its name from a telescope at which observatory?
La Silla in Chile
La Silla in Chile hosts the 60-centimetre TRAPPIST-South telescope, a Belgian-run robotic instrument whose 2016 detection of the first TRAPPIST-1 planets gave the system its name.
Q 20What is the informal nickname of HD 209458 b, the first exoplanet seen transiting its star?
Osiris
Osiris, named for the Egyptian god who was cut into pieces, fits a planet seen shedding hydrogen from its atmosphere in 2003 Hubble observations; it was also the first exoplanet with a detected atmosphere.
Q 24What was the first Earth-radius planet found in another star's habitable zone?
Kepler-186f
Kepler-186f, announced in April 2014, is about 1.1 times Earth's radius and the outermost of five planets around a red dwarf some 500 light-years away in Cygnus.
Q 25Which planet, announced in July 2015, was nicknamed 'Earth 2.0' or 'Earth's Cousin'?
Kepler-452b
Kepler-452b orbits a Sun-like star at 1.04 AU every 385 days and is about 1.6 times Earth's radius; a 2018 reanalysis questioned whether its transit signal was real.
Q 26Kepler-16b, found in 2011, was the first transiting example of what kind of world?
One orbiting two stars at once
One orbiting two stars at once: Kepler-16b, announced in September 2011, circles a pair of stars every 229 days, and its transits of both stars gave a radius precise to about 0.3 per cent.
Q 27Kepler-90i, found in 2017, made Kepler-90 the first system besides our own with how many known worlds?
Eight
Eight planets made Kepler-90 the first system to tie the Solar System's count; Kepler-90i was picked out of archival Kepler data in 2017 by a Google neural network trained to spot weak transits.
Q 28In which month and year was Kepler-22b, the first transiting planet in a Sun-like star's habitable zone, found?
December 2011
December 2011 brought the announcement of Kepler-22b, a 2.4-Earth-radius world 600 light-years away that orbits its Sun-like star every 290 days inside the habitable zone.
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, launched on a Falcon 9 on 18 April 2018 into a lunar-resonant orbit and took its first-light image on 7 August 2018; it targets nearby bright stars.
Q 30Which planet is the prototype of the 'hycean' class, with water under a hydrogen envelope?
K2-18b
K2-18b, a sub-Neptune 124 light-years away, became the model 'hycean' world after 2023 JWST spectra showed methane and carbon dioxide; a 2025 claim of a biosignature gas there was quickly disputed.