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Solar System quiz with answers
78 questions on the Sun, planets, moons, space flight and the universe. Read the question, think, then unfold the answer with the explanation. The full quiz with points and badges is in the 3D model.
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The Sun and the planets (19)
Which planet is closest to the Sun?
A) Earth B) Venus C) Mercury D) Mars
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Mercury. Mercury orbits the Sun in just 88 days at an average distance of 58 million km. More about Mercury
Which planet is the hottest – even though it is not the closest to the Sun?
A) Jupiter B) Mercury C) Venus D) Mars
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Venus. Venus's dense CO₂ atmosphere creates an extreme greenhouse effect: around 464 °C. More about Venus
Roughly how long does sunlight take to reach Earth?
A) About 8 seconds B) About 8 days C) About 8 hours D) About 8 minutes
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About 8 minutes. At a distance of 150 million km and the speed of light, it takes about 8 minutes and 20 seconds. More about Sun
Which is the largest planet in the Solar System?
A) Saturn B) Uranus C) Neptune D) Jupiter
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Jupiter. Jupiter has more than twice the mass of all the other planets put together. More about Jupiter
Which planet has the most striking ring system?
A) Saturn B) Venus C) Mercury D) Mars
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Saturn. Saturn's rings are made mostly of water ice and are extremely thin – often only about ten metres thick. More about Saturn
Which planet practically “rolls” around the Sun on its side (axial tilt about 98°)?
A) Saturn B) Uranus C) Neptune D) Mars
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Uranus. A giant impact early in its history probably tipped Uranus over. That is why its rings stand “upright”. More about Uranus
Which planet was first found by calculation rather than by observation?
A) Mars B) Neptune C) Saturn D) Uranus
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Neptune. Le Verrier and Adams calculated the position from disturbances in the orbit of Uranus – in 1846 Neptune was found there. More about Neptune
What is the name of the red storm on Jupiter that has been raging for almost two centuries?
A) Red Cyclone B) Great Red Spot C) Great Dark Spot D) Great Hexagon
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Great Red Spot. The Great Red Spot is an anticyclone that is still bigger than Earth but is slowly shrinking. More about Jupiter
Roughly how far is Earth from the Sun (1 astronomical unit)?
A) 15 million km B) 384,000 km C) 150 million km D) 1.5 billion km
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150 million km. 384,000 km, by the way, is the distance to the Moon. 1 AU is the basis for all distances in the Solar System. More about Earth
Which planet has the highest volcano in the Solar System (Olympus Mons, about 22 km)?
A) Mars B) Mercury C) Earth D) Venus
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Mars. Olympus Mons is an extinct shield volcano, around two and a half times as high as Mount Everest. More about Mars
How long is a day on Venus (one rotation on its axis) compared with its year?
A) Both are the same length B) A day on Venus is half as long as its year C) A day on Venus is longer than its year D) A day on Venus lasts 24 hours
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A day on Venus is longer than its year. Venus turns once in about 243 Earth days – its year lasts only about 225 Earth days. And it rotates backwards. More about Venus
What is the name of the giant canyon system on Mars?
A) Grand Canyon B) Valles Marineris C) Hellas Planitia D) Olympus Mons
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Valles Marineris. More than 4,000 km long and up to 7 km deep – it would stretch from New York to Los Angeles. More about Mars
What is the name of the highest mountain range on Venus?
A) Maat Mons B) Montes Apenninus C) Olympus Mons D) Maxwell Montes
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Maxwell Montes. About 11 km high – and the only major feature on Venus named after a man. More about Venus
Which impact triggered the extinction of the dinosaurs 66 million years ago?
A) Nördlinger Ries B) Chicxulub C) Vredefort D) Meteor Crater
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Chicxulub. The crater, about 180 km across, lies beneath Mexico's Yucatán Peninsula. More about Earth
What are Saturn's rings mostly made of?
A) Rock and iron B) Sand C) Gas D) Water ice
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Water ice. The chunks range from the size of a dust grain to the size of a house. That is why the rings shine so brightly. More about Saturn
Which planet has a giant hexagon at its north pole?
A) Jupiter B) Saturn C) Uranus D) Neptune
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Saturn. A jet stream forms an almost perfect hexagon there – each side is longer than Earth's diameter. More about Saturn
What colour is a sunset on Mars?
A) Blue B) Violet C) Green D) Red
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Blue. Fine Martian dust scatters the blue light in the direction of the Sun – exactly the other way round from Earth. More about Mars
How much of the total mass of the Solar System is in the Sun?
A) About 50% B) About 75% C) About 90% D) More than 99.8%
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More than 99.8%. All the planets, moons and asteroids together make up less than 0.2% – and most of that is Jupiter. More about Sun
What does a “light-year” measure?
A) A speed B) A brightness C) A length of time D) A distance
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A distance. The distance light travels in one year: about 9.5 trillion km. More about Sun
Moons (17)
How many moons does Earth have?
A) 0 B) 1 C) 2 D) 4
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1. The Moon is unusually large compared with its planet and keeps Earth's axis steady. More about Moon
Which moon of Jupiter is the most volcanically active body in the Solar System?
A) Ganymede B) Europa C) Callisto D) Io
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Io. Tidal forces from Jupiter and the neighbouring moons knead Io and heat up its volcanoes. More about Io
Beneath which icy shell is a global ocean of liquid water thought to lie – on a moon of Jupiter?
A) Moon (Earth) B) Callisto C) Europa D) Io
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Europa. Europa probably has twice as much water as all of Earth's oceans combined – a hot candidate for life. More about Europa
Which is the largest moon in the Solar System?
A) Titan B) Ganymede C) Callisto D) Moon (Earth)
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Ganymede. Ganymede is bigger than the planet Mercury and the only moon with its own magnetic field. More about Ganymede
Which moon of Saturn has a dense atmosphere and lakes of methane?
A) Rhea B) Io C) Titan D) Enceladus
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Titan. Titan is the only moon with a dense atmosphere. The European probe Huygens landed there in 2005. More about Titan
Which small moon of Saturn shoots fountains of water into space?
A) Enceladus B) Mimas C) Titan D) Rhea
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Enceladus. The fountains at the south pole come from an ocean beneath the ice and feed Saturn's E ring. More about Enceladus
Which moon looks like the “Death Star” from Star Wars because of a giant crater?
A) Phobos B) Tethys C) Mimas D) Rhea
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Mimas. The crater Herschel is 130 km wide – a third of the whole moon. More about Mimas
Which moon of Neptune orbits backwards and has nitrogen geysers?
A) Titania B) Charon C) Nereid D) Triton
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Triton. Triton was probably captured from the Kuiper Belt. In 1989 Voyager 2 saw geysers up to 8 km high. More about Triton
Which moon of Saturn is coal-black on one side and snow-white on the other?
A) Hyperion B) Dione C) Mimas D) Iapetus
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Iapetus. Iapetus sweeps up dark dust on its leading side; evaporating ice then makes the effect stronger and stronger. More about Iapetus
Which moon looks like a sponge and tumbles chaotically?
A) Miranda B) Deimos C) Hyperion D) Phobos
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Hyperion. Hyperion is about 40% empty space, and its rotation cannot be predicted. More about Hyperion
What are the two moons of Mars called?
A) Io and Europa B) Phobos and Deimos C) Castor and Pollux D) Titan and Rhea
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Phobos and Deimos. “Fear” and “Terror” – the sons of Ares, the god of war. Both were discovered by Asaph Hall in 1877. More about Phobos
Which moon has what is probably the highest cliff in the Solar System?
A) Miranda B) Ariel C) Moon (Earth) D) Oberon
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Miranda. Verona Rupes on Uranus's moon Miranda is up to 20 km high – a fall would take about 12 minutes. More about Miranda
Which moon is half the size of its dwarf planet?
A) Charon B) Nereid C) Phobos D) Triton
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Charon. Pluto and Charon orbit a shared point between them – almost a double planet. More about Charon
What are the moons of Uranus named after?
A) Characters from Shakespeare and Alexander Pope B) Norse giants C) Greek gods D) Roman emperors
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Characters from Shakespeare and Alexander Pope. Titania and Oberon, for example, come from “A Midsummer Night's Dream”, Ariel and Miranda from “The Tempest”. More about Titania
Why do we always see the same side of the Moon?
A) It turns on its axis exactly as fast as it orbits Earth B) It does not turn at all C) Earth hides the other side D) It is chance and changes every year
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It turns on its axis exactly as fast as it orbits Earth. This is called “tidal locking”. Earth's tidal forces slowed the Moon down until it turned like this. More about Moon
How many “Galilean moons” does Jupiter have?
A) 2 B) 4 C) 7 D) 12
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4. Io, Europa, Ganymede and Callisto – discovered in 1610 by Galileo Galilei with one of the first telescopes. More about Ganymede
Which of these moons is bigger than the planet Mercury?
A) Ganymede B) Europa C) Moon (Earth) D) Io
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Ganymede. Ganymede (5,268 km) and Titan too (5,150 km) are bigger than Mercury (4,879 km) – but much lighter. More about Ganymede
Dwarf planets and belts (11)
How many planets has our Solar System officially had since 2006?
A) 10 B) 7 C) 8 D) 9
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8. In 2006 the International Astronomical Union reclassified Pluto as a dwarf planet. More about Pluto
What is the heart-shaped region on Pluto?
A) An impact crater full of water B) A sea of liquid methane C) An extinct volcano D) It is a vast ice field (Tombaugh Regio)
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It is a vast ice field (Tombaugh Regio). In 2015 the New Horizons probe showed that the “heart” is made of nitrogen, methane and carbon monoxide ice. More about Pluto
Which dwarf planet lies in the Asteroid Belt?
A) Makemake B) Eris C) Ceres D) Pluto
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Ceres. Ceres contains about a third of the total mass of the Asteroid Belt. The Dawn probe visited it in 2015. More about Ceres
Which dwarf planet is about the size of Pluto but even heavier – and was discovered in 2005?
A) Ceres B) Makemake C) Eris D) Haumea
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Eris. Eris is about 27% more massive than Pluto. Its discovery led directly to the new definition of a planet. More about Eris
Which dwarf planet is shaped like a rugby ball because it spins so fast?
A) Haumea B) Eris C) Makemake D) Ceres
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Haumea. Haumea turns once on its axis in only about four hours – that stretches it into an ellipsoid. More about Haumea
Where is the Asteroid Belt?
A) Between Mars and Jupiter B) Between Saturn and Uranus C) Between Earth and Mars D) Beyond Neptune
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Between Mars and Jupiter. Jupiter's gravity prevented a planet from forming there. More about Asteroid Belt
What is the main difference between the Kuiper Belt and the Asteroid Belt?
A) It is made only of gas B) It is much smaller and denser C) It lies beyond Neptune and is made mostly of ice D) It lies between Earth and Mars and is made of metal
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It lies beyond Neptune and is made mostly of ice. The Kuiper Belt is about 20 times wider and more massive; Pluto, Eris, Makemake and Haumea orbit here. More about Kuiper Belt
Which probe flew past Pluto in 2015 and photographed its “heart”?
A) Rosetta B) New Horizons C) Voyager 2 D) Cassini
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New Horizons. New Horizons travelled for more than 9 years and then flew on to the Kuiper Belt object Arrokoth. More about Pluto
Which probe orbited the asteroids Vesta and Ceres one after the other?
A) Dawn B) Juno C) Hayabusa D) Galileo
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Dawn. Dawn was the first probe to orbit two different celestial bodies – made possible by its ion engine. More about Ceres
What is the name of the most distant object ever visited by a probe?
A) Eris B) Sedna C) Arrokoth D) Haumea
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Arrokoth. In 2019 New Horizons flew past Arrokoth, a snowman-shaped double body in the Kuiper Belt. More about Kuiper Belt
What are the bright spots in Occator crater on Ceres?
A) Salt deposits B) Frozen air C) Sulphur volcanoes D) Shiny lumps of metal
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Salt deposits. Salty water rose from the interior and evaporated – what was left behind is mainly sodium carbonate. More about Ceres
Space exploration (7)
Who was the first person to set foot on the Moon, in 1969?
A) Buzz Aldrin B) Neil Armstrong C) Michael Collins D) Yuri Gagarin
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Neil Armstrong. Armstrong climbed out first and Aldrin followed. Meanwhile Collins orbited the Moon alone in the command module. More about Moon
Who was the first person in space, in 1961?
A) Valentina Tereshkova B) Yuri Gagarin C) Neil Armstrong D) Alan Shepard
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Yuri Gagarin. On 12 April 1961 Gagarin circled Earth once – the flight lasted 108 minutes. More about Earth
How many people have stood on the Moon so far?
A) 2 B) 6 C) 12 D) 24
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12. Six Apollo missions landed on the Moon between 1969 and 1972, each with two astronauts. More about Moon
Which is the most distant object ever built by humans?
A) New Horizons B) Voyager 1 C) Voyager 2 D) Pioneer 10
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Voyager 1. Voyager 1 (launched 1977) is more than 25 billion km away – its radio signals take almost a day to reach Earth.
Which aircraft was the first to make a powered flight on another planet?
A) The Philae lander B) The Sojourner rover C) The Vega balloon D) The mini helicopter Ingenuity
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The mini helicopter Ingenuity. Ingenuity flew on Mars in 2021 – in an atmosphere only 1% as dense as Earth's. More about Mars
Which probe deliberately plunged into Saturn's atmosphere in 2017?
A) Juno B) Galileo C) Cassini D) Voyager 1
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Cassini. That way Cassini could not contaminate the moons Titan and Enceladus with microbes from Earth. More about Saturn
Which European probe landed on Saturn's moon Titan in 2005?
A) Huygens B) Rosetta C) Beagle 2 D) Philae
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Huygens. To this day, Huygens is the most distant landing from Earth ever made. More about Titan
Stars and galaxies (24)
Which star is closest to the Sun?
A) Vega B) Pole Star C) Sirius D) Proxima Centauri
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Proxima Centauri. Proxima Centauri is 4.2 light-years away – a small red dwarf that cannot be seen with the naked eye.
What is our galaxy called?
A) Milky Way B) Sombrero C) Large Magellanic Cloud D) Andromeda
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Milky Way. The Milky Way is a barred spiral about 100,000 light-years across.
Roughly how many stars does the Milky Way have?
A) 100 to 400 billion B) About 8,000 C) About 10 quadrillion D) About 1 million
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100 to 400 billion. They cannot be counted exactly – estimates range from 100 to 400 billion.
What sits at the centre of the Milky Way?
A) A giant star B) An empty space C) A gas planet D) A black hole
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A black hole. Sagittarius A* has the mass of about 4 million Suns. The first image of it was published in 2022.
Where is the Sun in the Milky Way?
A) Outside the Milky Way B) Right at the centre C) In a side arm, 26,000 ly from the centre D) Right at the outermost edge
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In a side arm, 26,000 ly from the centre. The Sun lies in the Orion Arm, about halfway between the centre and the edge.
How long does the Sun take to go once round the centre of the Milky Way?
A) About 10,000 years B) About 5 billion years C) One year D) About 230 million years
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About 230 million years. On its last lap, the first dinosaurs were just appearing on Earth.
What is the Orion Nebula?
A) A gas planet B) A distant galaxy C) A cloud of gas where stars are born D) The remains of an exploded star
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A cloud of gas where stars are born. A star-forming cloud 1,340 light-years away – visible to the naked eye as a misty patch in Orion's Sword.
Which nebula is the remnant of the stellar explosion that was observed in the year 1054?
A) Crab Nebula B) Orion Nebula C) Ring Nebula D) Horsehead Nebula
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Crab Nebula. Chinese astronomers saw the supernova for weeks at the time, even in the daytime sky.
Which large galaxy is our nearest neighbour?
A) The Whirlpool Galaxy B) The Sombrero Galaxy C) The Andromeda Galaxy D) The Pinwheel Galaxy
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The Andromeda Galaxy. Andromeda is 2.5 million light-years away – the most distant object you can easily see with the naked eye.
What do we know today about the future of the Milky Way and Andromeda?
A) They are flying apart B) They have already merged C) Andromeda will soon explode D) They are getting closer – a collision is possible
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They are getting closer – a collision is possible. Andromeda is approaching at 110 km/s. New measurements (2025) give a collision within the next 10 billion years about a 50:50 chance.
Which two companion galaxies of the Milky Way can only be seen from the southern sky?
A) The Hyades B) The Orion Clouds C) The Magellanic Clouds D) The Pleiades
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The Magellanic Clouds. Named after the navigator Magellan, whose crew described them in 1519.
Roughly how many galaxies belong to the Local Group?
A) Only 3 B) About 80 C) About 2,000 D) About 1 million
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About 80. Besides the Milky Way, Andromeda and the Triangulum Galaxy, they are mostly small dwarf galaxies – and new ones are being discovered all the time.
Which Swiss astronomer found the first evidence of dark matter in 1933?
A) Michel Mayor B) Albert Einstein C) Auguste Piccard D) Fritz Zwicky
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Fritz Zwicky. Zwicky saw that the galaxies in the Coma Cluster were whizzing about far too fast – there had to be invisible mass.
In 1995 two astronomers from Geneva found the first planet orbiting a Sun-like star. What is it called?
A) Kepler-22b B) 51 Pegasi b C) TRAPPIST-1e D) Proxima b
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51 Pegasi b. Michel Mayor and Didier Queloz received the 2019 Nobel Prize in Physics for it.
What is the name of the supercluster the Milky Way belongs to?
A) Andromeda Cluster B) Coma C) Perseus-Pisces D) Laniakea
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Laniakea. Laniakea is Hawaiian for “immeasurable heaven”. It was mapped out in 2014 and contains about 100,000 galaxies.
What are “voids” in the cosmic web?
A) Black holes B) Burnt-out stars C) Dark clouds of gas D) Vast, almost empty regions
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Vast, almost empty regions. Between the filaments of galaxies lie voids 30 to 300 million light-years across.
Who discovered in 1929 that the farther away galaxies are, the faster they are moving away?
A) Isaac Newton B) Edwin Hubble C) Galileo Galilei D) Nicolaus Copernicus
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Edwin Hubble. It follows that the universe is expanding. The Belgian Georges Lemaître had already predicted this in 1927.
What is it called when the light of distant galaxies appears redder?
A) Solar wind B) Aurora C) Sunset glow D) Redshift
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Redshift. Expanding space stretches the light waves – the farther away, the more strongly.
How old is the universe?
A) About 100 billion years B) About 4.6 billion years C) About 6,000 years D) About 13.8 billion years
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About 13.8 billion years. 4.6 billion years is the age of Earth and the Sun – the universe is three times as old.
How big is the observable universe (diameter)?
A) About 13.8 billion light-years B) About 93 billion light-years C) About 100,000 light-years D) About 1 billion light-years
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About 93 billion light-years. While the oldest light was on its way, space stretched. That is why it is bigger than its age would suggest.
What is the cosmic microwave background?
A) Radiation from black holes B) The oldest light, from 380,000 years after the Big Bang C) Radio waves from satellites D) The light of the Sun
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The oldest light, from 380,000 years after the Big Bang. That was when the universe became transparent. Today this light arrives as faint microwaves from every direction.
What is most of the universe made of?
A) Stars B) Planets C) Dark energy and dark matter D) Hydrogen gas
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Dark energy and dark matter. Ordinary matter – everything we know – makes up only about 5%.
Which telescope found the most distant known galaxies?
A) The telescope on the Moon B) Galileo's telescope C) The Sphinx Observatory on the Jungfraujoch D) The James Webb Telescope
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The James Webb Telescope. Webb sees in infrared. It found galaxies whose light had been travelling for about 13.5 billion years.
What does the famous Hubble Ultra Deep Field show?
A) A black hole B) About 10,000 galaxies in a tiny patch of sky C) Mars in close-up D) The surface of the Sun
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About 10,000 galaxies in a tiny patch of sky. The patch of sky is only about a tenth as wide as the Full Moon – and yet it is full of galaxies.
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