The Solar System Quiz — 7 Free Questions

Question 1

Which dwarf planet beyond Neptune spins so fast, once every four hours, that it has been stretched into the shape of a rugby ball, has two small moons, and in 2017 was found to be circled by a thin ring, the first ring discovered around a body of its kind?

Question 2

Which is a proposed vast spherical shell of trillions of icy bodies surrounding the entire solar system at its gravitational edge, perhaps a thousand to a hundred thousand times Earth's distance from the Sun, and the reservoir from which long-period comets fall inward?

Question 3

What is the technical term for the tilt of a planet's spin axis relative to the plane of its orbit, the quantity that gives a world its seasons, that is about 23.4 degrees for Earth and an extreme 98 degrees for Uranus, which therefore essentially orbits the Sun lying on its side?

Question 4

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 5

Which moon of Jupiter is the most volcanically active body in the solar system, dotted with hundreds of erupting vents that fling plumes of sulphurous gas and dust hundreds of kilometres up, and coloured in lurid yellows, oranges and reds that have earned it comparisons to a pizza?

Question 6

Which process powers the Sun and every other star, releasing energy by forcing light atomic nuclei to merge into heavier ones, with the mass of the product slightly less than the mass of the ingredients, the difference emerging as energy according to Einstein's famous equation?

Question 7

Which is the steady outward flow of electrically charged particles, mainly protons and electrons, escaping the Sun's corona in all directions at hundreds of kilometres per second, that blows comet tails back away from the Sun and, striking Earth's magnetic shield, lights up the polar auroras?

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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.