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Solar System

The planets, moons and missions of our Solar System, from Mercury to the Kuiper Belt, with the people who discovered them.

40 cards · Science

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Checked by the Brain Zap team · reviewed 10 Oct 2026

Source: Solar System (Wikipedia)

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  • Largest planet in the Solar System

    Show answer: Largest planet in the Solar System

    Jupiter

    Learn more: It has more than twice the mass of all the other planets put together; over 1,300 Earths would fit inside.

  • Planet closest to the Sun

    Show answer: Planet closest to the Sun

    Mercury

    Learn more: It orbits the Sun in 88 days. With almost no air, it swings from about 430 °C by day to −180 °C at night.

  • Hottest planet in the Solar System

    Show answer: Hottest planet in the Solar System

    Venus

    Learn more: Its thick carbon dioxide air traps heat, keeping the surface at about 465 °C, hotter than Mercury's.

  • Planet known as the Red Planet

    Show answer: Planet known as the Red Planet

    Mars

    Learn more: Iron oxide, rust, in its dust gives it its colour. A year there lasts 687 Earth days.

  • Farthest planet from the Sun

    Show answer: Farthest planet from the Sun

    Neptune

    Learn more: Its position was worked out from Uranus's wobbles before it was first seen, in 1846.

About this topic

The Solar System is our neighbourhood in space: one star, eight planets, their moons, and countless smaller bodies, from asteroids between Mars and Jupiter to the icy worlds of the Kuiper Belt and the far Oort Cloud. It formed from one cloud of gas and dust about 4.6 billion years ago.

Knowing it makes the night sky, space news and every new mission easier to follow, and it shows how unusual and fragile Earth is next to its neighbours.

The planets are easier to learn in order from the Sun, in two groups: four small rocky worlds, then four giants. Each one has a stand-out fact that sticks: Mercury is closest, Venus hottest, Mars red, Jupiter biggest, Saturn ringed, Uranus on its side and Neptune farthest. Hang the moons, missions and astronomers on the planet they belong to.

All 40 cards

  1. Largest planet in the Solar System

    Jupiter

    Learn more: It has more than twice the mass of all the other planets put together; over 1,300 Earths would fit inside.

  2. Planet closest to the Sun

    Mercury

    Learn more: It orbits the Sun in 88 days. With almost no air, it swings from about 430 °C by day to −180 °C at night.

  3. Hottest planet in the Solar System

    Venus

    Learn more: Its thick carbon dioxide air traps heat, keeping the surface at about 465 °C, hotter than Mercury's.

  4. Planet known as the Red Planet

    Mars

    Learn more: Iron oxide, rust, in its dust gives it its colour. A year there lasts 687 Earth days.

  5. Farthest planet from the Sun

    Neptune

    Learn more: Its position was worked out from Uranus's wobbles before it was first seen, in 1846.

  6. Planet that rotates on its side

    Uranus

    Learn more: Its axis is tilted about 98 degrees, perhaps from an ancient collision, so it rolls around the Sun on its side.

  7. Number of planets in the Solar System

    8

    Learn more: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Pluto was reclassified in 2006.

  8. Current classification of Pluto

    A dwarf planet

    Learn more: The IAU ruled that a planet must clear its orbit. Pluto shares its orbit with other Kuiper Belt objects.

  9. Year the IAU reclassified Pluto

    2006

    Learn more: The International Astronomical Union voted on 24 August in Prague to define a planet, leaving Pluto out.

  10. Largest moon in the Solar System

    Ganymede

    Learn more: It is the only moon known to have its own magnetic field. Galileo discovered it in 1610.

  11. Saturn's largest moon

    Titan

    Learn more: It has lakes and seas of liquid methane and ethane. The Huygens probe landed on it in 2005.

  12. Name of Jupiter's giant long-lived storm

    The Great Red Spot

    Learn more: Watched since at least 1830, and maybe the 1600s. It is shrinking, but is still wider than Earth.

  13. Tallest volcano on Mars

    Olympus Mons

    Learn more: This shield volcano rises about 22 km and is some 600 km across. Mars's weak gravity let it grow so large.

  14. The two planets the asteroid belt lies between

    Mars and Jupiter

    Learn more: Jupiter's gravity kept these bodies from forming a planet. Together they weigh less than our Moon.

  15. Largest object in the asteroid belt

    Ceres

    Learn more: Found in 1801, it was called a planet, then an asteroid, and since 2006 a dwarf planet. The Dawn probe orbited it.

  16. How long sunlight takes to reach Earth

    About 8 minutes

    Learn more: Sunlight crosses about 150 million km to reach us, taking 8 minutes and 20 seconds on average.

  17. Average distance from Earth to the Sun

    About 150 million km

    Learn more: This distance defines the astronomical unit, about 149.6 million km. It varies by about 5 million km over a year.

  18. First crewed mission to land on the Moon

    Apollo 11

    Learn more: It landed in the Sea of Tranquillity on 20 July 1969. Michael Collins stayed in orbit in the command module.

  19. First person to walk on the Moon

    Neil Armstrong

    Learn more: He stepped onto the Moon in July 1969, saying 'That's one small step for man, one giant leap for mankind'.

  20. Year of the first crewed Moon landing

    1969

    Learn more: Apollo 11 landed on 20 July, meeting Kennedy's 1961 goal of a Moon landing before the decade was out.

  21. First artificial satellite to orbit Earth

    Sputnik 1

    Learn more: A 58 cm metal ball launched on 4 October 1957, it beeped for three weeks and started the Space Race.

  22. First human in space

    Yuri Gagarin

    Learn more: On 12 April 1961 he orbited Earth once in 108 minutes. The date is now the International Day of Human Space Flight.

  23. First spacecraft to reach interstellar space

    Voyager 1

    Learn more: It crossed the heliopause into interstellar space in 2012, and is the farthest human-made object from Earth.

  24. Planet best known for its bright rings

    Saturn

    Learn more: Its rings are mostly ice, from grains to house-sized chunks, yet in most places only about 10 m thick.

  25. The two moons of Mars

    Phobos and Deimos

    Learn more: Both are small and lumpy, and may be captured asteroids. The inner one is slowly spiralling inward.

  26. Most volcanically active body in the Solar System

    Io

    Learn more: Tides from Jupiter's gravity squeeze it and heat its interior, powering hundreds of active volcanoes.

  27. Neptune's largest moon

    Triton

    Learn more: Its backward orbit suggests it was captured from the Kuiper Belt. Voyager 2 saw geysers on it in 1989.

  28. Pluto's largest moon

    Charon

    Learn more: About half Pluto's size, so the pair orbit a point between them, always showing each other the same face.

  29. Most abundant element in the Sun

    Hydrogen

    Learn more: By mass the Sun is about 73% hydrogen and 25% helium. It fuses hydrogen into helium in its core.

  30. Process that powers the Sun

    Nuclear fusion

    Learn more: In its core, at about 15 million °C, hydrogen nuclei fuse into helium, turning a little mass into energy.

  31. Icy region beyond Neptune that includes Pluto

    The Kuiper Belt

    Learn more: A ring of icy bodies beyond Neptune, about 30 to 50 AU from the Sun. New Horizons flew past one, Arrokoth, in 2019.

  32. Distant shell of icy bodies, source of long-period comets

    The Oort Cloud

    Learn more: A theorised shell of icy bodies up to about 100,000 AU away. A passing star can nudge one inward as a comet.

  33. Famous comet seen from Earth roughly every 75 years

    Halley's Comet

    Learn more: Edmond Halley predicted its return for 1758, after his death. It was last seen from Earth in 1986.

  34. Astronomer whose Sun-centred model was published in 1543

    Nicolaus Copernicus

    Learn more: His book De revolutionibus put the Sun at the centre; it came out in 1543, the year he died.

  35. Astronomer who discovered Jupiter's four largest moons

    Galileo Galilei

    Learn more: In 1610 he saw Io, Europa, Ganymede and Callisto orbiting Jupiter: proof that not everything circles Earth.

  36. Astronomer who discovered Uranus in 1781

    William Herschel

    Learn more: Uranus was the first planet found with a telescope. He first took it for a comet, then named it after George III.

  37. Astronomer who discovered Pluto in 1930

    Clyde Tombaugh

    Learn more: He found Pluto in 1930 by comparing photographic plates. Some of his ashes flew past Pluto on New Horizons.

  38. Spacecraft that flew past Pluto in 2015

    New Horizons

    Learn more: It flew past Pluto in July 2015 and sent the first close-up images, including its heart-shaped plain.

  39. Approximate age of the Solar System

    About 4.6 billion years

    Learn more: The oldest solids in meteorites, calcium-rich grains, formed about 4.57 billion years ago.

  40. Infrared space telescope launched in December 2021

    James Webb Space Telescope

    Learn more: It orbits about 1.5 million km from Earth, at L2, behind a sunshield the size of a tennis court.

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