Authors:

I think it was because [Nikola] Tesla and [Leon] Theremin were part of what made up the movie, The Day the Earth Stood Still. Klaatu was actually a European among the Americans. And so the person who wrote the story said that Klaatu came from Europa, the fourth moon of Jupiter, which is now being investigated for life. There's water and ice on it and that kind of stuff.

Source: www.paranoiamagazine.com
I think it was because [Nikola] Tesla and [Leon] Theremin were part of what made up the movie, The Day the Earth Stood Still. Klaatu was actually a European among the Americans. And so the person who wrote the story