Planet records and the outer reaches
Planet records and the outer reaches: a chapter of The Solar System Book, from the biggest planet to the icy edge.
15 cards · Science
Each Zap teaches up to 5 new cards, so you learn the deck a few at a time.
Checked by the Brain Zap team · reviewed 23 Oct 2026
Sources: Solar System (Wikipedia), Solar System (NASA Science)
Preview
Planet closest to the Sun
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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
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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
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Mars
Learn more: Iron oxide, rust, in its dust gives it its colour. A year there lasts 687 Earth days.
Largest planet in the Solar System
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Jupiter
Learn more: It has more than twice the mass of all the other planets put together; over 1,300 Earths would fit inside.
Farthest planet from the Sun
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Neptune
Learn more: Its position was worked out from Uranus's wobbles before it was first seen, in 1846.
About this topic
Which planet is the biggest, the hottest, the farthest, the one that spins on its side? After the records come our Moon's biggest cousins, Pluto, the icy Kuiper Belt and, far beyond, the Oort Cloud where comets are born.
This is a chapter of The Solar System Book. Some of its cards show the planets moving around the Sun at their real relative speeds, with one planet glowing: name it. Others ask for the facts that make each world special, with a hint before you answer and a short reason after. Once you know most of this chapter's cards, the next chapter starts arriving in your Daily Zap.
All 15 cards
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
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
Mars
Learn more: Iron oxide, rust, in its dust gives it its colour. A year there lasts 687 Earth days.
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.
Farthest planet from the Sun
Neptune
Learn more: Its position was worked out from Uranus's wobbles before it was first seen, in 1846.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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.
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