The Sun and the rocky planets
The Sun and the rocky planets: a chapter of The Solar System Book, with planets you watch move on their orbits and the facts behind them.
11 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
Glowing on the orbit: the smallest planet
Show answerHide answer: Glowing on the orbit: the smallest planet
Mercury
Learn more: It circles the Sun in just 88 days, the shortest year of any planet.
Glowing on the orbit: Earth's cloudy neighbour
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Venus
Learn more: It spins backwards, and so slowly that its day lasts longer than its year.
Glowing on the orbit: the third planet
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Earth
Learn more: The only planet known to have liquid water on its surface, and life.
Glowing on the orbit: the fourth planet
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Mars
Learn more: A year there lasts 687 Earth days, almost two of ours.
Most abundant element in the Sun
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Hydrogen
Learn more: By mass the Sun is about 73% hydrogen and 25% helium. It fuses hydrogen into helium in its core.
About this topic
The Sun holds more than 99 percent of the Solar System's mass and lights everything in it. Close to it orbit four small, rocky worlds: scorched Mercury, cloudy Venus, our blue Earth and red, dusty Mars.
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 11 cards
Glowing on the orbit: the smallest planet
Mercury
Learn more: It circles the Sun in just 88 days, the shortest year of any planet.
Glowing on the orbit: Earth's cloudy neighbour
Venus
Learn more: It spins backwards, and so slowly that its day lasts longer than its year.
Glowing on the orbit: the third planet
Earth
Learn more: The only planet known to have liquid water on its surface, and life.
Glowing on the orbit: the fourth planet
Mars
Learn more: A year there lasts 687 Earth days, almost two of ours.
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.
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.
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.
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.
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.
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.
Number of planets in the Solar System
8
Learn more: Mercury, Venus, Earth, Mars, Jupiter, Saturn, Uranus and Neptune. Pluto was reclassified in 2006.
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