Solar System Size Quiz
Which of these two objects is bigger across?
▲▼ Play Solar System Size Quiz
The scale of the solar system is close to impossible to hold in your head, which is exactly what makes this mode work. Objects are compared by mean diameter, and the categories you expect to dominate often do not.
Two moons — Ganymede and Titan — are both larger than the planet Mercury. Meanwhile Deimos, one of Mars's two moons, would barely cover a mid-sized city.
Planets, moons, dwarf planets and asteroids all appear together, so never assume that a planet automatically outranks a moon. That single assumption ends more runs in this category than anything else.
Things worth knowing
- Ganymede and Titan are both larger than Mercury
- Deimos is only about 12 km across
- Planets, moons and dwarf planets compete together
How it works
You are shown two items side by side. One reveals its number; the other hides it behind a question mark. Decide whether the hidden value is higher or lower, and every correct call extends your streak. One wrong guess ends the run. If the two values are equal the answer counts as correct either way, so a tie never costs you anything. The game is free, runs entirely in your browser, and needs no account.