Finally, someone who explains it as I do. My students say "It is, its and it's are a bit confusing". I say, " If the word is either possessive or a contraction and the student is really reading the sentence, then you should be able to identify how it is used." Thank you.
Because it's a pronoun (*wink*), "it" follows the same forms as other pronouns: he's, she's and it's; his, her and its. "Its" is closest in actual form to "his," and surely no one would be tempted to include an apostrophe in "his" - even in a culture wherein the current U.S. President's name has drawn more than its (*wink*) fair share of apostrophes.