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
More than 6,300 have been confirmed as of mid-2026, in over 4,700 systems.
Q 02Around what kind of object were the first confirmed exoplanets found in 1992?
A pulsar
Aleksander Wolszczan and Dale Frail found two terrestrial-mass planets orbiting PSR B1257+12.
Q 03Which two astronomers announced the first exoplanet around a Sun-like star, 51 Pegasi b, in October 1995?
Michel Mayor and Didier Queloz
They worked at the Observatoire de Haute-Provence and shared a 2019 Nobel Prize.
Q 04What official proper name did the IAU give 51 Pegasi b?
Dimidium
It is Latin for 'half', for the planet's roughly half-Jupiter mass.
Q 0551 Pegasi b is the prototype of which class of exoplanet?
Hot Jupiters
Gas giants orbiting scorchingly close to their stars turned out to be common among early discoveries.
Q 06What are the names of the three planets orbiting the neutron star PSR B1257+12?
Draugr, Poltergeist and Phobetor
The pulsar itself was named Lich; all are undead creatures from folklore.
Q 07What is the least massive exoplanet known, at about twice the mass of the Moon?
Draugr
It orbits the pulsar Lich.
Q 08Which two methods have discovered the most exoplanets?
Transit photometry and Doppler spectroscopy
Both are biased towards finding 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
That is 0.008 per cent, which is why space telescopes are needed.
Q 10What was the first exoplanet discovered by the transit method, in 2002?
OGLE-TR-56b
HD 209458 b had been the first seen transiting in 1999, but was found first by radial velocity.
Q 11The radial velocity method detects a planet by measuring what?
The star's small orbital wobble
A star with a planet moves in its own tiny orbit in response to the planet's gravity.
Q 12Which detection method uses a star's gravity to magnify a distant background star?
Gravitational microlensing
NASA's Roman Space Telescope, due in 2027, will run a microlensing planet survey.
Q 13What is the IAU's working mass limit separating planets from brown dwarfs?
13 times Jupiter
It is the threshold for thermonuclear fusion of deuterium in objects of solar metallicity.
Q 21In which year did NASA launch the Kepler space telescope?
2009
Ironically, Johannes Kepler was convinced no other stars had planetary systems.
Q 22Approximately how many stars did Kepler continually monitor in its fixed field of view?
150,000
Its single instrument was a photometer watching for tiny dips in brightness.
Q 23Why was Kepler retired in October 2018?
Its fuel ran out
It had operated for nine and a half years, finding 2,778 confirmed planets by 2023.
Q 24What was the first Earth-radius planet found in another star's habitable zone?
Q 14By convention, the first planet discovered around a star gets which letter?
b
The star counts as 'a', and later planets get subsequent letters in order of discovery.
Q 15How far away are the nearest known exoplanets, which orbit Proxima Centauri?
4.2 light-years
Proxima b was announced by ESO in August 2016 after the Pale Red Dot campaign.
Q 16What is the orbital period of Proxima Centauri b?
About 11.2 days
It orbits at just 0.048 AU, yet sits in its dim red dwarf's habitable zone.
Q 17Who led the team that announced Proxima Centauri b in 2016?
Guillem Anglada-Escudé
Their Pale Red Dot project confirmed years of Doppler measurements.
Q 18How many known planets orbit the ultra-cool red dwarf TRAPPIST-1?
Seven
They take between 1.5 and 19 days to orbit, and the star is about 40 light-years away in Aquarius.
Q 19TRAPPIST-1 takes its name from a telescope at which observatory?
La Silla in Chile
The Transiting Planets and Planetesimals Small Telescope found the first two planets in 2016; five more followed in 2017.
Q 20What is the informal nickname of HD 209458 b, the first exoplanet seen transiting its star?
Osiris
It was also the first found with an atmosphere, one seen evaporating hydrogen.
Kepler-186f
It is the outermost of five planets around a red dwarf.
Q 25Which planet, announced in July 2015, was nicknamed 'Earth 2.0' or 'Earth's Cousin'?
Kepler-452b
It orbits a Sun-like star at 1.04 AU every 385 days, though its status is now disputed.
Q 26Kepler-16b was the first confirmed example of what kind of world?
One orbiting two stars at once
The 'Tatooine' comparison was inevitable; its radius was known to within 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
Google's machine-learning method found it in old Kepler data.
Q 28In which month and year was Kepler-22b, the first transiting planet in a Sun-like star's habitable zone, found?
December 2011
Liquid water could in principle exist on its surface.
Q 29Which satellite, launched on a Falcon 9 in April 2018, surveys 85% of the sky for transiting planets?
TESS
Its first light image was taken on 7 August 2018.
Q 30Which planet is the prototype of the 'hycean' class, with water under a hydrogen envelope?
K2-18b
JWST found water vapour, carbon dioxide and methane; a 2025 biosignature claim was quickly disputed.