Mercury Trivia
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59 free Mercury trivia questions with answers — science & nature quiz, new questions added Sep 2026.
This Mercury trivia quiz is about the planet, the smallest and swiftest of the eight. It covers the basics that surprise people: an 88-day year but a 176-day solar day, a 3:2 spin-orbit lock instead of tidal locking, six-hundred-degree temperature swings and yet water ice in polar craters, an oversized iron core, the most eccentric orbit and the smallest axial tilt. It then visits the surface: the giant Caloris Basin, the Weird Terrain opposite it, the Spider crater, and the naming rules that put Beethoven and Tolstoj on the map. The exploration and history questions follow Mariner 10's slingshot past Venus, MESSENGER's orbit and final crash, and BepiColombo's six flybys, then go back to Gassendi's transit, Zupi's phases, Soviet and Arecibo radar, Le Verrier's phantom planet Vulcan and the 43 arcseconds that Einstein explained. A final group looks at the name: the Roman messenger god and his May festival, Greek Stilbon, Babylonian Nabu, the Chinese water star, Wednesday, and the Maya owl. 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.
30 of 59 questions with answers and explanations. Play the quiz
Q 01Mercury became the smallest planet when which world was reclassified as a dwarf planet?
Pluto
Pluto was demoted in 2006 after astronomers found comparable worlds such as Eris, leaving eight planets with Mercury the smallest.
Q 02About how long is a year on Mercury?
About 3 months
About 3 months: Mercury laps the Sun every 88 Earth days, so a 30-year-old on Earth would be over 120 in Mercury years.
Q 03A sunrise-to-sunrise day on Mercury lasts about twice as long as what?
Its own year
Its own year: Mercury turns so slowly as it circles the Sun that one side bakes in daylight for a whole Mercury year, then faces a year of night.
Q 04Astronomers long believed Mercury kept one face toward the Sun; what did radar reveal instead?
Three spins per two orbits
Three spins per two orbits: whenever Mercury was best placed for viewing, it happened to show the same side, which made it look locked.
Q 05Despite being closest to the Sun, Mercury is only the second-hottest planet. Which is hotter?
Venus
Mercury has almost no atmosphere to trap heat, whereas Venus is wrapped in a thick greenhouse blanket.
Q 06Mercury's day side gets hot enough to melt which of these metals?
Lead
Lead melts at about 327 °C, and Mercury's equator tops 400 °C by day before plunging to around −170 °C at night.
Q 07What is the name of Mercury's largest crater, about a third the diameter of the planet?
Caloris Planitia
Caloris Planitia: lava later flooded the giant basin, burying its original floor beneath volcanic plains.
Q 08Which Mercury Seven astronaut became the first American in space?
Alan Shepard
Alan Shepard flew a 15-minute hop aboard Freedom 7, and a decade later he hit two golf balls on the Moon.
Q 09What is the nickname of the hilly region on the exact opposite side of Mercury from its largest impact basin?
The Weird Terrain
The Weird Terrain may have formed when shock waves from the giant impact raced around the planet and converged on the far side, fracturing the ground.
Q 10Which science-fiction writer set his short story 'Runaround' on Mercury?
Isaac Asimov
Isaac Asimov's 'Runaround' first spelled out his Three Laws of Robotics: its robot circles a pool of selenium, trapped between two of the laws.
Q 11Craters on Mercury are named after what kind of people?
Artists, musicians and authors
Artists, musicians and authors qualify only once they have been dead for more than three years, which is how Walt Disney came to have a crater there.
Q 12Mercury's mountains (montes) are named after what?
The word 'hot' in various languages
The word 'hot' in various languages; Mercury's long cliffs, which rose as the planet shrank, are named for ships of discovery instead.
Q 13Roughly what share of Mercury's volume does its metallic core fill?
About 60%
Q 21Which spacecraft became the first to orbit Mercury?
MESSENGER
MESSENGER entered orbit in 2011 and by 2013 had mapped the whole planet, of which the only earlier visitor had seen less than half.
Q 22How did the first Mercury orbiter's mission end?
It crashed into the planet's surface
It crashed into the planet's surface in April 2015, after running out of the propellant it needed to hold its orbit.
Q 23BepiColombo, the mission to orbit Mercury, is a joint project of ESA and which other agency?
Japan's JAXA
Japan's JAXA built Mio, one of the mission's two orbiters, and the pair travelled to Mercury stacked on a European transfer module.
About 60%: Mercury's iron core fills about 57% of the planet's volume, which makes this small world the second-densest planet.
Q 14Mercury has the second-highest density of any planet. Which is first?
Earth
Factor out gravitational squeezing and Mercury's raw material is actually denser than Earth's.
Q 15What has been confirmed to exist in permanently shadowed craters at Mercury's poles?
Water ice
Water ice survives on the planet nearest the Sun inside polar craters that sunlight never reaches, and radio telescopes first spotted it in the early 1990s.
Q 16Mercury's axis is almost perfectly upright; which planet is tipped so far that it spins on its side?
Uranus
Uranus is tilted about 98°, perhaps after a collision with an Earth-sized body, while Mercury's axis leans only about 0.03°.
Q 17Mercury has the most eccentric orbit of the eight planets; which planet's orbit is the next most oval?
Mars
Mars: its oval path defied every circular model, and Tycho Brahe's observations of it revealed that planets travel in ellipses.
Q 18What did the first probe to visit Mercury surprisingly discover about the small planet?
A magnetic field
A magnetic field, only about 1% as strong as Earth's, yet it can twist with the solar wind's field into 'magnetic tornadoes' that funnel hot plasma down to the ground.
Q 19Which was the first spacecraft to fly past Mercury?
Mariner 10
Mariner 10 kept working until its attitude-control gas ran out in March 1975, and controllers then switched it off for good.
Q 20Which technique did the first probe to reach Mercury pioneer on its way there?
A gravity assist
A gravity assist: Luna 3 had borrowed the Moon's pull in 1959, but this probe was the first to swing past one planet to reach another.
Q 24BepiColombo honours Giuseppe Colombo, whose calculations let the first Mercury probe do what?
Return for repeat flybys
Return for repeat flybys: Colombo showed that after its first pass the probe's own orbit round the Sun would bring it back, and it met Mercury three times.
Q 25Why did BepiColombo need six flybys of Mercury before it could enter orbit?
To shed speed
To shed speed: a probe falling toward the Sun keeps gaining speed, so each close pass slowed it relative to Mercury until it could be captured.
Q 26What was the hidden planet Le Verrier proposed inside Mercury's orbit called?
Vulcan
Vulcan seemed a safe bet, because Le Verrier had already found Neptune by the same method, yet searches over the next half-century never turned it up.
Q 27Which theory explained the extra 43 arcseconds per century in Mercury's perihelion advance?
Einstein's general relativity
Einstein's general relativity explained it in 1915 as the Sun's mass curving spacetime, removing any need for an unseen planet.
Q 28The first transit of Mercury ever observed had been predicted by which astronomer?
Johannes Kepler
Johannes Kepler forecast it in tables published in 1630, but he died that November, less than a year before Mercury crossed the Sun as he had said.
Q 29Which US coin was nicknamed for the god Mercury, though its winged head actually shows Liberty?
The dime
The dime: Adolph Weinman's winged Liberty was later revived on the American Palladium Eagle, a bullion coin struck since 2017.
Q 30Which NASA mathematician did astronaut Glenn insist check the computer's calculations before his flight?
Katherine Johnson
Katherine Johnson checked the numbers, and Glenn, who had said he was ready to go if she called them good, flew a successful mission.