Yes the burden of proof is on you. And in this analogy, the tea cups of saturn have been regularly observed for decades, so you have your work cut out for you.
Yes the burden is still on you. You're not just claiming you have not yet seen sufficient evidence of something existing, you are claiming it explicitly doesn't exist, ie that there has been some search conducted that should have found it if it had been there, but got a null result.
Of course in this case, not only can the tea cup be seen by Earth's telescopes, pictures of it are widely published in every book on saturn.
Is the burden of proof still on me? Why?