60 free Mercury trivia questions with answers — science & nature quiz, new questions added Aug 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 60 questions with answers and explanations. Play the quiz
Q 01Where does Mercury rank in distance from the Sun?
First (closest)
It is also the smallest of the eight planets, smaller even than the moons Ganymede and Titan.
Q 02How long is a year on Mercury, in Earth days?
88
Its orbit is the fastest of any planet, which is why the Romans named it after their swift messenger god.
Q 03How long does one solar day (sunrise to sunrise) last on Mercury?
About 176 Earth days
That is twice its year: one side bakes for a full 88-day orbit and then freezes for the next.
Q 04Mercury rotates three times for every two orbits of the Sun. What is this relationship called?
A 3:2 spin–orbit resonance
Astronomers had assumed it was tidally locked, like the Moon, until 1965 radar observations proved otherwise.
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 06Roughly what temperature range does Mercury's equator experience between night and day?
About −170 °C to 420 °C
The swing of nearly 600 degrees is the largest of any planet.
Q 07What is the name of Mercury's largest crater, about a third the diameter of the planet?
Caloris Planitia
Its rim of mountains stands about 2 km high and the impact sent shock waves right around the planet.
Q 08What is the diameter of Mercury's largest impact basin?
1,550 km
The planet itself is only 4,880 km across.
Q 09What is the nickname of the hilly region on the exact opposite side of Mercury from the Caloris Basin?
The Weird Terrain
One theory is that shock waves from the impact travelled round the planet and met there.
Q 10Which crater on Mercury is nicknamed 'the Spider' for its radiating troughs?
Apollodorus
It sits inside the Caloris Basin and its origin is still debated.
Q 11Craters on Mercury are named after what kind of people?
Artists, musicians and authors
Hence craters called Beethoven, Tolstoj and Rembrandt; ridges get scientists and valleys get abandoned ancient cities.
Q 12Mercury's mountains (montes) are named after what?
The word 'hot' in various languages
The escarpments, or rupes, are the ones named for ships of scientific expeditions.
Q 13Roughly what fraction of Mercury's volume is taken up by its iron core?
About 57%
Earth's core is only about 17% of its volume; Mercury's may be the leftover of a planet stripped by a giant impact.
Q 21Which spacecraft became the first to orbit Mercury, in March 2011?
MESSENGER
Its name is a backronym for Mercury Surface, Space Environment, Geochemistry, and Ranging.
Q 22How did the first Mercury orbiter's mission end in April 2015?
It crashed into the planet's surface
With its propellant gone, controllers used the helium pressurant to squeeze out a few extra weeks first.
Q 23BepiColombo, launched in 2018 to orbit Mercury, is a joint mission between ESA and which other agency?
Japan's JAXA
It carries two orbiters, one to map the planet and one to study its magnetosphere.
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
Radar from Earth first spotted the bright patches in the early 1990s; orbiter images later confirmed the ice.
Q 16Mercury's axial tilt is the smallest of any planet, at about how much?
0.03 degrees
An observer at the poles would never see the centre of the Sun rise above the horizon.
Q 17Mercury's orbit is the most eccentric of the eight planets. What is its eccentricity?
0.21
Its distance from the Sun swings between about 46 and 70 million km.
Q 18Mercury's magnetic field, first measured in the 1970s, is roughly what fraction of Earth's strength?
About 1%
Its existence surprised scientists, who thought the planet spun far too slowly to run a dynamo.
Q 19Which was the first spacecraft to fly past Mercury, in 1974?
Mariner 10
It was also the first probe to use a gravitational slingshot, swinging past Venus on the way.
Q 20Which planet's gravity did the first Mercury flyby probe use as a slingshot to get there?
Venus
The manoeuvre was proposed by Italian scientist Giuseppe Colombo, after whom BepiColombo is named.
Q 24The ESA-JAXA Mercury orbiter is named after Giuseppe Colombo, who first proposed what technique?
The interplanetary gravity assist
Mariner 10 used his idea in 1974, and nearly every planetary probe has used it since.
Q 25How many Mercury flybys did BepiColombo complete by its last one in January 2025?
Six
The first was in October 2021 and the sixth in January 2025; its two orbiters were then due to enter orbit around Mercury in late 2026.
Q 26What was the hidden planet Le Verrier proposed in 1859 inside Mercury's orbit called?
Vulcan
It was never found; Einstein's general relativity explained the extra precession in the 20th century.
Q 27Which theory finally explained the unexplained 43 arcseconds per century in Mercury's perihelion advance?
Einstein's general relativity
It became one of the three classic tests of the theory, alongside light bending and gravitational redshift.
Q 28Transits of Mercury across the Sun can only happen in which two months?
May or November
They occur about every seven years on average, when Mercury crosses the ecliptic while between Earth and the Sun.
Q 29Who made the first telescopic observation of a planetary transit, watching Mercury cross the Sun in 1631?
Pierre Gassendi
Kepler had predicted the transit; Gassendi was the one who saw it.
Q 30Who, in 1639, used a telescope to show Mercury has phases like the Moon, proving it orbits the Sun?
Giovanni Zupi
Marius had already suspected phases in 1612 from the planet's changing brightness.