Beyond the answers - interesting background to this quiz

A moon with a atmosphere thicker than Earth's

Titan is Saturn's largest moon and the second-largest moon in the solar system, after Jupiter's Ganymede. It is the only moon known to have a substantial atmosphere, and that atmosphere is denser than Earth's. Its surface is cold enough for methane and ethane to exist as liquids, forming lakes and rivers, which is one reason scientists take such a close interest in it.

Why tungsten hides behind a W

The chemical symbol for tungsten is W, which looks like a mismatch until you meet the element's other name: wolfram. That name comes from the German mineral wolframite, and it survives in several European languages, where the metal is still called wolfram. English kept the Swedish-derived word "tungsten," meaning "heavy stone," but the symbol followed the older name.

A language that outlived an empire

Latin was the language of Ancient Rome, and it did not disappear when the empire did. It evolved into the modern Romance languages, including Italian, Spanish, French, Portuguese and Romanian, and remained the language of scholarship and the Catholic Church in Europe for centuries. Roman numerals, another Roman inheritance, are still used today on clock faces and in the names of monarchs and popes.

The Alps as a European crossroads

The Alps stretch across several European countries, including France, Switzerland, Italy, Austria and Slovenia. Rather than a single wall of rock, they are a system of ranges shaped by glaciers, with passes that have carried traders, pilgrims and armies for thousands of years. Their peaks also feed major rivers such as the Rhine and the Po.

A sequence with a simple rhythm

The sequence 3, 9, 15, 21, 27 moves in steps of six, so the next term is 33. Patterns like this are called arithmetic sequences, and they turn up in everything from seating plans to savings goals. Spotting the constant difference is usually the fastest way in, though not every puzzle is quite so well behaved.