A five-year-old boy has been told it would cost about $US25,000 to send a letter to Mars.
Britain's Royal Mail turned to NASA for help in answering Oliver Giddings' question.
In its reply to the five-year-old, who wants to become an astronaut, the Royal Mail explained how the figure was calculated, saying fuel was very expensive.
The Royal Mail said the price of the letter would be covered by 18,416 first class stamps.
- AFP