"Buenas Noches, Planeta is a short story about a stuffed little deer, that my actual daughter has, and when I asked her what's the name of your new friend she said "Planeta," which is planet in English, and I thought it was the weirdest, funniest, coolest name I have ever heard for a stuffy. So then the story came out of that."
January 1, 1970
https://en.wikiquote.org/wiki/Liniers_(cartoonist)