Asked by: David Smith, London
The longest known single journey was that of a Doctor Who postcard in a bottle, thrown into the sea at Tyne and Wear in 2011. This turned up 17 months later in Perth, Western Australia – over 14,500km away. But in 1929, German marine scientists dropped a bottle into the Indian Ocean with instructions for the finder to report where it washed up and then throw it back. This floated for six years and covered 25,600km!
Subscribe to BBC Focus magazine for fascinating new Q&As every month and follow @sciencefocusQA on Twitter for your daily dose of fun science facts.