Because it was deep space. (the joke is how the outer space was very deep)
Ripostes them
The punchline for this joke is 0.99$
Some people may call it a log journal, while others call it a diary-a.
X-post) http://www.reddit.com/r/AskHistorians/comments/2krnv8/whatistheoldestjokewehaveonrecord/
Because I hear that in space there is no ice-cream.
It's a vacuum!