The Solar System Quiz — 10 Free Questions

Question 1

What is the name of the outer boundary where the Sun's wind of particles finally loses its push against the thin gas drifting between the stars, marking the edge of the Sun's own bubble in the galaxy, and crossed by Voyager 1 in 2012 and Voyager 2 in 2018?

Question 2

According to the definition adopted by the International Astronomical Union in 2006, a full planet must orbit the Sun and be massive enough to have pulled itself into a round shape, and must also have done what to the region around its orbit, something Pluto has failed to do because it shares its zone with many other icy bodies?

Question 3

Which body was counted as the ninth planet from its discovery in 1930 until 2006, when astronomers reclassified it as a dwarf planet because, unlike a full planet, it has not swept its orbital zone clear of other sizeable objects?

Question 4

What is the name for the line dividing the sunlit side from the dark side of a moon or planet, the boundary of day and night that sweeps across the surface as the body rotates, and along which, on the Moon, the low grazing sunlight throws long shadows that make craters and mountains stand out most sharply to a telescope?

Question 5

Which feature is a colossal spinning storm in the atmosphere of Jupiter, an anticyclone wide enough to swallow the Earth whole, that has been watched through telescopes for at least 190 years and possibly much longer, though it has been shrinking and growing rounder in recent decades?

Question 6

Which is the Sun's faint, pearly outer atmosphere, streaming millions of kilometres into space, that is heated to one or two million degrees, far hotter than the surface below it by a mechanism still not fully understood, and is normally lost in glare but springs into view during a total solar eclipse?

Question 7

Which small, dazzlingly white, ice-covered moon of Saturn jets fountains of water vapour and ice grains hundreds of kilometres into space from cracks near its south pole nicknamed 'tiger stripes', feeding one of Saturn's faint outer rings and revealing a salty ocean beneath its shell?

Question 8

Which self-reinforcing process is thought to have turned Venus from a possibly Earth-like young world into the furnace it is today, as rising heat evaporated its water, the water vapour trapped still more heat, and eventually the oceans boiled away entirely, leaving a dense blanket of carbon dioxide?

Question 9

What name is given to the photograph taken by Voyager 1 in 1990 from about 6 billion kilometres away, in which the Earth is a single almost invisible pixel, caught by chance in a scattered ray of sunlight, prompting a famous reflective essay on the smallness of human affairs?

Question 10

Which is the largest moon of Pluto, so big in proportion, about half Pluto's width, that the two do not simply orbit each other but both swing around a balance point in the empty space between them, so that some astronomers call the pair a double dwarf planet?

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About The Solar System

The solar system is the Sun and everything gravity binds to it: eight planets, hundreds of moons, several dwarf planets, and uncountable asteroids, comets and grains of dust, all left over from the collapse of one cloud of gas 4.6 billion years ago. This quiz is a tour of about eighty of its members and features. Each question describes one, a planet, a moon, a surface feature, a small body, a phenomenon or a term, and asks you to name it from four choices, then explains what it is, how we know, and the striking fact or the common mistake attached to it.

It works outward from the Sun. Mercury's baked and frozen rock; Venus and its runaway furnace; Mars with the tallest volcano and longest canyon anywhere; the gas giants Jupiter and Saturn with their storms, rings and swarms of moons; the tipped-over ice giants Uranus and Neptune. Then the moons that are worlds in their own right: volcanic Io, ocean-hiding Europa and Enceladus, hazy Titan with its methane lakes, backward-orbiting Triton. And the debris: the asteroid belt, the Kuiper belt, the distant Oort cloud, comets and their tails, meteoroids and meteorites.

A recurring theme is that the solar system is a snapshot of a violent history. The Moon was blasted off a young Earth by a Mars-sized impact. Mercury and the Moon are cratered from an ancient bombardment. Saturn's rings may be debris from a shattered moon, young enough that dinosaurs saw a bare Saturn. Triton was stolen from the Kuiper belt. Uranus was knocked on its side. The planets themselves grew by countless collisions of smaller bodies.

It also gives real weight to the physics and the bookkeeping that make sense of it all: the astronomical unit and the light-minute; obliquity, eccentricity and what actually causes seasons; the frost line that split the small rocky planets from the gas giants; the Roche limit that shreds a moon into a ring; the Lagrange points where a telescope can park; tidal locking, libration, retrograde motion, spring and neap tides; and why a total solar eclipse is possible only because of a 400-to-400 coincidence that will not last forever.

The quiz also sorts out the confusions: meteoroid versus meteor versus meteorite, why Pluto was demoted, why an 'artery' rule about oxygen has an exception, that the asteroid belt is mostly empty space, that a comet's tail does not trail behind it but points away from the Sun. Because so much of the imagery for these worlds comes from space agencies and is in the public domain, questions carry a photograph wherever one helps without giving the answer away, often a picture of the parent planet for a question about one of its moons. Every claim has been checked against reliable sources, and the wording is kept plain.