SOLVED. Children's book on space travel to the moon - 1950s [s]

[Susan]

When I was in elementary school in the 1980s, I read a book from the 1950s (I think 1959), about a boy who traveled to the moon and found it inhabited by strange creatures - like floating bubbles maybe, or large flowers. Does this sound familiar to anyone? There may have been a cat or other animal companion, too.

[El]

Susan, do you remember how the boy traveled to the moon? Like by rocket or anything?

[bup]

Well, a few near-misses would be Space Cat, Space Cat Visits Venus, and Space Cat Meets Mars.

All those are decidedly about the cat, more than the human (who is a man, not a boy). However, there's one detail match in each book.

In Space Cat, he goes to the moon.
In Space Cat Visits Venus, he meets intelligent flowering plants.
In Space Cat Meets Mars, there are fish that send large bubbles into the air.

All these books are from the 1950's.

[Lobstergirl, au gratin]

I think bup is right - "Space Cat" also features living, thinking bubbles and "plants that survive without atmosphere", according to Back in the Spaceship Again: Juvenile Science Fiction Series Since 1945. The cat's name is Flyball.

[Susan]

I bet that's it - Space Cat! That makes sense because I was really into cats then, and I had liked the Disney movie The Cat from Outer Space.

Wow, this is awesome. Thank you so much.