Whose Moon is it Anyway? Trivia Quiz

Answer: Mars

Discovered by American astronomer Asaph Hall in 1877, Phobos is the closer of the two moons orbiting Mars. It is irregularly shaped and has a radius of just 11km (less than seven miles). Because it orbits Mars faster than Mars itself rotates on its axis, from the surface of Mars it appears to rise in the west and set in the east.

Phobos transits in front of the Sun nearly every day as viewed from the Martian surface, and these transits have even been photographed in time-lapse by the "Opportunity" Mars Rover.

Answer: Mars

Also discovered by Asaph Hall in 1877, a few days after he discovered Phobos, Deimos is the further of the two moons orbiting Mars. It is also irregularly shaped and is even smaller than Phobos with a radius of just 6.2km (less than four miles). Due to its small size and distance, it appears star-like from the Martian surface.

At its brightest, during its full moon, it appears about as bright as Venus does from Earth. It too transits the Sun regularly and this phenomenon has also been photographed by Martian rovers.

Answer: Jupiter

Ganymede is the largest moon in the Solar System with a radius of 2634km (over 1600 miles), almost half that of the Earth, making it larger than the planet Mercury. It is one of the four "Galilean moons" of Jupiter discovered by Galileo Galilei in 1610.

With a surface of mostly silicate rock and water ice, evidence suggests the presence of a large subsurface ocean, perhaps the largest in the Solar System. This ocean may be habitable, making Ganymede a target of interest in the search for extra-terrestrial life.

Answer: Jupiter

Europa is the smallest of the four "Galilean moons" orbiting Jupiter, and has also been determined to feature a subsurface ocean. The "Europa Clipper" probe mission was launched in 2024 with the aim of further understanding the potential habitability of the moon's ocean and determining a landing site for a proposed mission to land a probe on the surface of the moon.

The probe will arrive in 2030, meaning Europa could be the first place extra-terrestrial life will be confirmed to exist.

Answer: Saturn

Slightly smaller than Ganymede, Titan is the second largest moon in the Solar System and it is also larger than the planet Mercury. However, it only has 40% of the mass of Mercury due to its low density composition of ice and rocky material. It is the only moon with an atmosphere more dense than the Earth's, with an air pressure 1.448 times that of the Earth at their respective surfaces.

The "Huygens" probe landed on the surface of Titan in 2005 and sent back the only photo from the surface of a Solar System body permanently beyond Mars.

Answer: Saturn

Coming in at only the sixth largest moon of Saturn, Enceladus owes its outsized name-recognition to the presence of yet another subsurface ocean. With the "Cassini" probe's detection of water-rich plumes venting from the surface, Enceladus became one of the first promising sites for the presence of extra-terrestrial life.

However, at the time of this quiz being written in early 2025 there has not been a dedicated mission sent to Enceladus to investigate this further.

Answer: Uranus

Titania is the largest moon of Uranus. It is named after the queen of the fairies in Shakespeare's "A Midsummer Night's Dream", in keeping with the theme of naming Uranus's moons after Shakespeare characters, plus some from a poem by Alexander Pope. Additionally, its surface features are named for female characters or locations from Shakespeare's works.

It orbits within Uranus's magnetosphere, meaning it is bombarded by magnetospheric plasma as it orbits.

Answer: Uranus

Oberon is the second largest of Uranus's moons, and was discovered in 1787 along with Titania by William Herschel, discoverer of Uranus itself. It is named after the king of the fairies in Shakepeare's "A Midsummer Night's Dream". As with Uranus and its other moons, its axis of rotation and orbit is inclined at almost 90 degrees to the ecliptic (the plane in which the planets orbit).

This means the north and south poles experience extreme seasons, with 42 years of continuous sunlight alternating with 42 years of continuous darkness.

Answer: Neptune

Triton is the largest moon of Neptune, discovered just 17 days after the planet itself. It is the only large moon in the Solar System in a retrograde orbit (orbiting opposite the direction of its planet's rotation), suggesting it could be a captured dwarf planet from the Kuiper Belt (a region beyond Neptune containing asteroids and dwarf planets), which would make it quite similar in origin to Pluto, Eris and other trans-Neptunian dwarf planets.

Despite this origin, it has a nearly perfectly circular orbit, in contrast to the slightly more elliptical orbits of most planets and moons.

Answer: Neptune

Nereid is the third largest moon of Neptune and the last to be discovered by telescope prior to the arrival of the "Voyager 2" probe. Despite being imaged directly by the probe 83 times, the surface features and shape of Nereid are currently unknown due to the low resolution of the images. However, based on its mass, it is highly likely it has an irregular asteroid-like shape.

Similar to Triton, it has an irregular orbit and thus is thought to be a captured asteroid or Kuiper Belt object, though it is too small to be a dwarf planet like Triton.