Solar System Quiz
On one planet, a day lasts longer than a year.
A solar system quiz with answers that goes beyond naming the planets in order: extreme temperatures, strange tilts, giant volcanoes and moons with weather of their own.
Did you know?
- Saturn is the least dense planet in the solar system, on average lighter than water. In theory it would float if a large enough ocean existed. Its rings, although hundreds of thousands of kilometres across, are in most places only about ten metres thick.
- Ganymede, a moon of Jupiter, is the largest moon in the solar system and is bigger than the planet Mercury. It is also the only moon known to generate its own magnetic field, and it probably hides a salt-water ocean beneath its icy crust.
- Uranus was the first planet discovered with a telescope. William Herschel spotted it from his garden in the English city of Bath in 1781 and at first took it for a comet. He wanted to name it after King George III, a suggestion that did not catch on abroad.
A short tour of the solar system
The solar system formed about 4.6 billion years ago from a rotating cloud of gas and dust. Most of the material fell to the centre and became the Sun, which still holds about 99.8 per cent of the system's mass. The rest gathered into planets, moons, asteroids and comets. Everything orbits in roughly the same flat plane and in the same direction, a leftover of that original spinning disc.
Rock and gas
The four planets closest to the Sun are small and rocky. Farther out, where it was cold enough for ice to form, planets could grow much larger and hold on to light gases. That is why the outer four are giants: two made mainly of hydrogen and helium, and two that contain more water, ammonia and methane and are often called ice giants. Between the two groups lies a belt of rocky debris that never became a planet.
Worlds with weather
Many of these worlds are far from quiet. A storm larger than the Earth has been turning on Jupiter for at least a century and a half. The longest day belongs to a planet that spins so slowly, and backwards, that the Sun rises in the west. Several moons are thought to hide oceans of liquid water beneath shells of ice, which makes them among the most interesting places to search for signs of life.
The edge and beyond
Beyond the last planet lies a wide ring of icy bodies, including several dwarf planets, and much farther out a vast cloud of comets is thought to surround the whole system. Distances here are hard to picture. Two spacecraft launched in 1977 have been travelling outward ever since, and the faster of them only crossed into the space between the stars in 2012.