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Space & Astronomy Easy ⚡ 10 Questions ⏱️ ~6 Mins +100 XP

The Planets, Properly

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Everyone learns the order of the planets and then stops. This is the next layer: which one is actually hottest, which one spins backwards, and which one is not named after a god.

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~6m

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Easy

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+100

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About this topic

The eight planets are usually taught as a sequence to be recited, which hides how strange they are individually. Venus turns the wrong way. Uranus lies on its side. Jupiter has been running the same storm for longer than anyone has been watching it. Every question here turns on a property you can hold in your head rather than a figure to memorise. If you get one wrong, the explanation should tell you why the obvious answer felt right and where it goes astray.

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The Planets, Properly: all 10 questions and answers

Every question in this quiz is listed below with its correct answer and the reasoning behind it. Play first if you would rather not see the answers — or read through as a study sheet.

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1Which planet orbits closest to the Sun?
- A Mars
- B Mercury Correct
- C Venus
- D Earth
Answer: B. Mercury

Why: Mercury orbits at roughly 58 million kilometres, well inside Venus. It is not the hottest planet though, because it has almost no atmosphere to hold the heat in.
2Which planet has the hottest surface?
- A Venus Correct
- B Mercury
- C Mars
- D Jupiter
Answer: A. Venus

Why: Venus sits at roughly 465 degrees Celsius, hot enough to melt lead, thanks to a thick carbon dioxide atmosphere. Mercury is closer to the Sun but its night side drops hundreds of degrees below freezing.
3On which planet is a single rotation longer than a full orbit of the Sun?
- A Mercury
- B Mars
- C Neptune
- D Venus Correct
Answer: D. Venus

Why: Venus takes about 243 Earth days to turn once but only about 225 to go round the Sun, so its day outlasts its year. It also rotates backwards compared with almost everything else in the solar system.
4The Great Red Spot is a storm on which planet?
- A Neptune
- B Uranus
- C Jupiter Correct
- D Saturn
Answer: C. Jupiter

Why: The spot is a high-pressure storm in Jupiter's southern hemisphere that astronomers have tracked continuously since the nineteenth century. It has been shrinking for as long as anyone has measured it carefully.
5Which planet is tipped roughly 98 degrees, so that it effectively rolls along its orbit?
- A Mars
- B Uranus Correct
- C Neptune
- D Saturn
Answer: B. Uranus

Why: Uranus has an axial tilt of about 98 degrees, most likely the result of an enormous early collision. Each pole spends roughly 42 years in continuous sunlight and then 42 years in darkness.
6Olympus Mons, the tallest volcano in the solar system, stands on which planet?
- A Mars Correct
- B Venus
- C Mercury
- D Earth
Answer: A. Mars

Why: Olympus Mons rises roughly 22 kilometres, around two and a half times the height of Everest. Mars has no moving tectonic plates, so the volcano sat over the same hotspot and simply kept growing.
7Saturn's rings are made mostly of what?
- A Iron dust
- B Liquid methane
- C Volcanic rock
- D Water ice Correct
Answer: D. Water ice

Why: The rings are overwhelmingly water ice, in pieces ranging from grains to boulders. They span well over 200,000 kilometres across yet are only tens of metres thick in most places.
8Which planet is not named after a Greek or Roman deity?
- A Saturn
- B Mercury
- C Earth Correct
- D Neptune
Answer: C. Earth

Why: Earth comes from Old English and Germanic words simply meaning ground or soil. It is the only planet whose name was never borrowed from mythology.
9Which planet has the strongest surface gravity?
- A Earth
- B Jupiter Correct
- C Saturn
- D Neptune
Answer: B. Jupiter

Why: Gravity at Jupiter's cloud tops is roughly two and a half times Earth's. Saturn is nearly as large but so much less dense that its surface gravity is only slightly above our own.
10Which planet takes roughly 165 Earth years to complete one orbit of the Sun?
- A Neptune Correct
- B Uranus
- C Saturn
- D Jupiter
Answer: A. Neptune

Why: Neptune is the outermost planet and needs about 165 years to get round once. It was discovered in 1846 and only completed its first full orbit since then in 2011.

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