Solar System Quiz
Planets, moons, rings and dwarf planets: 15 questions on everything that orbits our Sun.
Which planet is closest to the Sun?
Got a hunch? Pick the answer that feels right.
Mercury
Mercury orbits at an average of about 58 million km (36 million miles) from the Sun and completes a lap in just 88 Earth days. Despite being closest, it is not the hottest planet, because it has almost no atmosphere to trap heat.
A day on Mercury, from one sunrise to the next, lasts 176 Earth days, twice as long as its year.
Which planet is famous for its bright, wide ring system?
Got a hunch? Pick the answer that feels right.
Saturn
Saturn's rings are made mostly of chunks of water ice ranging from dust grains to house-sized boulders. The main rings span about 280,000 km (175,000 miles) across yet are mostly less than a kilometer thick.
Galileo saw the rings in 1610 but thought they were two moons; Christiaan Huygens correctly identified a ring in 1655.
Which planet is often called Earth's twin because of its similar size and mass?
Got a hunch? Pick the answer that feels right.
Venus
Venus is about 95 percent of Earth's diameter and 80 percent of its mass, but its thick carbon dioxide atmosphere traps heat and bakes the surface at around 465 °C (870 °F), hot enough to melt lead.
Venus spins backwards compared with most planets, so the Sun there rises in the west and sets in the east.
Which former planet was reclassified as a dwarf planet in 2006?
Got a hunch? Pick the answer that feels right.
Pluto
The International Astronomical Union voted in August 2006 that a planet must clear its orbital neighborhood, which Pluto does not, so it became a dwarf planet after 76 years as the ninth planet.
The discovery of Eris in 2005, at first thought to be bigger than Pluto, forced astronomers to decide what counts as a planet.
What is the name of the giant storm that has raged on Jupiter for centuries?
Got a hunch? Pick the answer that feels right.
The Great Red Spot
The Great Red Spot is an anticyclone wider than Earth that has been observed continuously since at least the 1830s. Its winds reach hundreds of kilometers per hour, and the storm has been shrinking in recent decades.
The Great Dark Spot was a similar storm on Neptune seen by Voyager 2 in 1989, but it had vanished by the time Hubble looked in 1994.
The main asteroid belt lies between the orbits of which two planets?
Got a hunch? Pick the answer that feels right.
Mars and Jupiter
The belt lies between Mars and Jupiter, where Jupiter's powerful gravity prevented the rocky debris from clumping into a planet. Despite containing millions of asteroids, its total mass is less than that of the Moon.
The asteroids are so spread out that spacecraft pass through the belt without any special maneuvers to avoid collisions.
Olympus Mons, the largest volcano in the solar system, is on which planet?
Got a hunch? Pick the answer that feels right.
Mars
Olympus Mons rises about 21 km (13 miles), nearly two and a half times the height of Mount Everest, and its base is roughly the size of Arizona. Mars's low gravity and lack of plate tectonics let it grow so huge.
The volcano's slopes are so gentle that an astronaut standing on it would not be able to tell they were on a mountain at all.
What is the largest moon in the solar system?
Got a hunch? Pick the answer that feels right.
Ganymede
Jupiter's moon Ganymede has a diameter of about 5,268 km (3,273 miles), making it larger than the planet Mercury. It is the only moon known to generate its own magnetic field.
Ganymede was one of the four moons Galileo discovered in January 1610, the first objects ever seen orbiting another planet.
Which planet was the first to be discovered using a telescope, in 1781?
Got a hunch? Pick the answer that feels right.
Uranus
William Herschel spotted Uranus from his garden in Bath, England, in March 1781, at first thinking it was a comet. The five planets closer to the Sun had all been known since ancient times, so the discovery doubled the known size of the solar system.
Herschel wanted to name the planet Georgium Sidus after King George III, a suggestion that did not go down well outside Britain.
Which moon of Saturn has a thick atmosphere and lakes of liquid methane?
Got a hunch? Pick the answer that feels right.
Titan
Titan is the only moon with a dense atmosphere, and its surface holds rivers, lakes and seas of liquid methane and ethane at around minus 180 °C (minus 290 °F). The Huygens probe landed there in 2005.
NASA's Dragonfly mission, a nuclear-powered rotorcraft, is designed to fly from site to site across Titan's surface in the 2030s.
Which planet was discovered in 1846 after its position was predicted mathematically?
Got a hunch? Pick the answer that feels right.
Neptune
Urbain Le Verrier calculated where an unseen planet must be from wobbles in the orbit of Uranus, and Johann Galle found Neptune within a degree of that spot on the first night he looked, September 23, 1846.
Neptune has completed only one full orbit of the Sun since its discovery, finishing its first lap in 2011.
Which dwarf planet is the largest object in the asteroid belt?
Got a hunch? Pick the answer that feels right.
Ceres
Ceres is about 940 km (585 miles) across and holds roughly a third of the belt's total mass. Discovered in 1801, it was called a planet, then an asteroid, and finally a dwarf planet in 2006.
NASA's Dawn spacecraft orbited Ceres from 2015 and found bright salt deposits and signs of a briny reservoir beneath the surface.
Roughly how often does Halley's Comet return to the inner solar system?
Got a hunch? Pick the answer that feels right.
About every 76 years
Halley's Comet has an average period of about 76 years, though gravitational nudges shift individual returns to between 74 and 79 years. It last passed close to the Sun in 1986 and is due back in 2061.
Edmond Halley never saw the return he predicted: he died in 1742 and the comet came back on schedule in 1758.
How many planets in our solar system have ring systems?
Got a hunch? Pick the answer that feels right.
Four
All four giant planets, Jupiter, Saturn, Uranus and Neptune, have rings. Saturn's are the only ones bright enough to see with a small telescope; the others are dark and thin and were found by spacecraft and by watching stars blink behind them.
Uranus's rings were discovered in 1977 when the planet passed in front of a star and the starlight blinked several times before and after.
Which moon is the most volcanically active world in the solar system?
Got a hunch? Pick the answer that feels right.
Io
Jupiter's moon Io is kneaded by the gravity of Jupiter and its neighboring moons, which heats its interior and powers hundreds of volcanoes that spray sulfur plumes hundreds of kilometers into space.
Io's volcanoes were discovered by Voyager 1 in 1979, the first active volcanoes ever seen beyond Earth.
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All Science quizzes →About the Solar System Quiz
Our solar system is stranger than the classroom poster suggests. Jupiter's moon Ganymede is bigger than the planet Mercury, a volcano on Mars stands nearly two and a half times taller than Everest, and Saturn's rings are so thin that if the planet were the size of a football field, they would be thinner than a sheet of paper.
These 15 questions cover the eight planets, their most famous moons, the asteroid belt, Halley's Comet and the dwarf planets that caused all the fuss in 2006. The first questions are easy for anyone who remembers the order of the planets, the middle section explores moons and discoveries, and the last few will test real space enthusiasts. Play it before your next clear night sky.
You will find 15 multiple choice questions here, each with four options. Difficulty: Medium. Most people finish in about 6 minutes, and every answer comes with a short explanation and one extra fact worth keeping.
How to play
Read the question and pick one of the four answers. The correct answer is revealed straight away with a short explanation, then press Next question to keep going. At the end you get your score out of 15 and a full review of your round. Play again any time and the questions arrive in a fresh order. There is no timer and no account.
Good to know before you play
Is Pluto in this quiz?
Yes. One question covers Pluto's 2006 reclassification as a dwarf planet, and another features Ceres, the dwarf planet in the asteroid belt.
How is this different from the Space and Astronomy Quiz?
This quiz stays inside the solar system, focusing on planets, moons, asteroids and comets rather than galaxies, telescopes and the wider universe.
What is the hardest question?
Players usually struggle with how many planets have rings and which moon is the most volcanically active. Both answers are explained in full.
Answer key: all 15 questions with explanations
- Which planet is closest to the Sun?
Mercury Mercury orbits at an average of about 58 million km (36 million miles) from the Sun and completes a lap in just 88 Earth days. Despite being closest, it is not the hottest planet, because it has almost no atmosphere to trap heat. A day on Mercury, from one sunrise to the next, lasts 176 Earth days, twice as long as its year. - Which planet is famous for its bright, wide ring system?
Saturn Saturn's rings are made mostly of chunks of water ice ranging from dust grains to house-sized boulders. The main rings span about 280,000 km (175,000 miles) across yet are mostly less than a kilometer thick. Galileo saw the rings in 1610 but thought they were two moons; Christiaan Huygens correctly identified a ring in 1655. - Which planet is often called Earth's twin because of its similar size and mass?
Venus Venus is about 95 percent of Earth's diameter and 80 percent of its mass, but its thick carbon dioxide atmosphere traps heat and bakes the surface at around 465 °C (870 °F), hot enough to melt lead. Venus spins backwards compared with most planets, so the Sun there rises in the west and sets in the east. - Which former planet was reclassified as a dwarf planet in 2006?
Pluto The International Astronomical Union voted in August 2006 that a planet must clear its orbital neighborhood, which Pluto does not, so it became a dwarf planet after 76 years as the ninth planet. The discovery of Eris in 2005, at first thought to be bigger than Pluto, forced astronomers to decide what counts as a planet. - What is the name of the giant storm that has raged on Jupiter for centuries?
The Great Red Spot The Great Red Spot is an anticyclone wider than Earth that has been observed continuously since at least the 1830s. Its winds reach hundreds of kilometers per hour, and the storm has been shrinking in recent decades. The Great Dark Spot was a similar storm on Neptune seen by Voyager 2 in 1989, but it had vanished by the time Hubble looked in 1994. - The main asteroid belt lies between the orbits of which two planets?
Mars and Jupiter The belt lies between Mars and Jupiter, where Jupiter's powerful gravity prevented the rocky debris from clumping into a planet. Despite containing millions of asteroids, its total mass is less than that of the Moon. The asteroids are so spread out that spacecraft pass through the belt without any special maneuvers to avoid collisions. - Olympus Mons, the largest volcano in the solar system, is on which planet?
Mars Olympus Mons rises about 21 km (13 miles), nearly two and a half times the height of Mount Everest, and its base is roughly the size of Arizona. Mars's low gravity and lack of plate tectonics let it grow so huge. The volcano's slopes are so gentle that an astronaut standing on it would not be able to tell they were on a mountain at all. - What is the largest moon in the solar system?
Ganymede Jupiter's moon Ganymede has a diameter of about 5,268 km (3,273 miles), making it larger than the planet Mercury. It is the only moon known to generate its own magnetic field. Ganymede was one of the four moons Galileo discovered in January 1610, the first objects ever seen orbiting another planet. - Which planet was the first to be discovered using a telescope, in 1781?
Uranus William Herschel spotted Uranus from his garden in Bath, England, in March 1781, at first thinking it was a comet. The five planets closer to the Sun had all been known since ancient times, so the discovery doubled the known size of the solar system. Herschel wanted to name the planet Georgium Sidus after King George III, a suggestion that did not go down well outside Britain. - Which moon of Saturn has a thick atmosphere and lakes of liquid methane?
Titan Titan is the only moon with a dense atmosphere, and its surface holds rivers, lakes and seas of liquid methane and ethane at around minus 180 °C (minus 290 °F). The Huygens probe landed there in 2005. NASA's Dragonfly mission, a nuclear-powered rotorcraft, is designed to fly from site to site across Titan's surface in the 2030s. - Which planet was discovered in 1846 after its position was predicted mathematically?
Neptune Urbain Le Verrier calculated where an unseen planet must be from wobbles in the orbit of Uranus, and Johann Galle found Neptune within a degree of that spot on the first night he looked, September 23, 1846. Neptune has completed only one full orbit of the Sun since its discovery, finishing its first lap in 2011. - Which dwarf planet is the largest object in the asteroid belt?
Ceres Ceres is about 940 km (585 miles) across and holds roughly a third of the belt's total mass. Discovered in 1801, it was called a planet, then an asteroid, and finally a dwarf planet in 2006. NASA's Dawn spacecraft orbited Ceres from 2015 and found bright salt deposits and signs of a briny reservoir beneath the surface. - Roughly how often does Halley's Comet return to the inner solar system?
About every 76 years Halley's Comet has an average period of about 76 years, though gravitational nudges shift individual returns to between 74 and 79 years. It last passed close to the Sun in 1986 and is due back in 2061. Edmond Halley never saw the return he predicted: he died in 1742 and the comet came back on schedule in 1758. - How many planets in our solar system have ring systems?
Four All four giant planets, Jupiter, Saturn, Uranus and Neptune, have rings. Saturn's are the only ones bright enough to see with a small telescope; the others are dark and thin and were found by spacecraft and by watching stars blink behind them. Uranus's rings were discovered in 1977 when the planet passed in front of a star and the starlight blinked several times before and after. - Which moon is the most volcanically active world in the solar system?
Io Jupiter's moon Io is kneaded by the gravity of Jupiter and its neighboring moons, which heats its interior and powers hundreds of volcanoes that spray sulfur plumes hundreds of kilometers into space. Io's volcanoes were discovered by Voyager 1 in 1979, the first active volcanoes ever seen beyond Earth.
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