I'm wondering what the proper punctuation is when using "as is" to make a comparison.
Example: "Venus and Mars are planets, as is Earth when referring to the whole world."
I've noticed in this answer regarding a different use of "as is" the poster uses a comma, and in this question regarding non-adverbial uses of as-is the poster also includes a comma before "as is".
This was my first instinct, but when looking back over the sentence, I wasn't sure anymore. Is the second half of the sentence parenthetical (and thus belong in parentheses), or if the comma is correct, then why? Are both sides of the sentence independent clauses? If they are not independent clauses then should there be any punctuation at all?